In a recent video, Red Beard revisits testing of the MoFlow billet cylinder head, this time evaluating how the engine responds to increased displacement along with updated valvetrain components. This includes a different camshaft and rocker arm combination, both critical factors in maximizing small engine performance for kart racing and mini bike applications.

In the original test, Red Beard used the Tillotson 225 platform. At the time, this engine was considered a major upgrade over the common 212cc clone engines used in kart racing and mini bikes. The Tillotson 225 gained popularity due to its strong value, featuring a factory billet connecting rod and a lightweight, racing-style piston—components that made it ideal for performance builds right out of the box.

Since then, many builders have pushed the platform further by increasing displacement to 236cc. This configuration has become a common and affordable setup in the 14.5ci open class in kart racing, offering a noticeable gain in torque and horsepower while maintaining reliability when properly assembled.

For the original test, Red Beard used the Tillotson 225-based platform to dyno the MoFlow billet cylinder head, which features a 32mm intake valve and a 25mm exhaust valve. The setup included Gage 1.3 ratio roller rockers paired with a 356 camshaft, resulting in a total valve lift of .462”.

While the engine produced strong power numbers, it encountered valve float just above 7,000 RPM. Further inspection revealed that the issue was caused by interference between the Gage roller rockers and the valve retainers—a critical clearance issue that limited high-RPM stability.

This serves as an important reminder for anyone building performance small engines for kart racing or mini bikes: most aftermarket components are not truly “plug and play.” Proper setup, measurement, and clearance checks are essential to prevent performance loss—or worse, catastrophic damage to expensive engine components.

Updating to the Tillotson 236cc: Camshaft and Valvetrain Changes

In the updated test video, the entire engine combination has been revised. The platform is now based on a Tillotson 236cc engine, increasing overall displacement, piston speed, and compression compared to the earlier 225 setup. These changes alone significantly impact torque production and overall small engine performance, especially in kart racing and mini bike applications.

The valvetrain has also been reconfigured. The billet cylinder head is now paired with EC 1.4 ratio Rev roller rockers and a .308 camshaft, resulting in a total valve lift of .431”. Compared to the previous .356 camshaft (.462” total lift), the .308 features reduced duration and less overlap.

This change was intentional—aimed at creating a more street-friendly power curve. By reducing duration and overlap, the engine benefits from improved idle quality, stronger low-end torque, and better throttle response, which are all critical for mini bike performance and recreational riding applications.

The .308 camshaft has become a staple in the small engine performance world. It is one of the most widely used, tested, and documented camshafts available today. Popularized across multiple builds, it has been featured extensively by Red Beard’s Garage on projects such as the “Road to Horsepower” Predator 212, Predator 224, and now the Tillotson 236.

Using the same camshaft across different engine platforms provides valuable insight into how a single component performs under varying conditions. In this case, the .308 cam helps highlight how camshaft selection influences power delivery, rideability, and overall engine behavior across multiple displacements and combinations.

Overall, the updated 236cc combination performed well, particularly in improving low- to mid-range power characteristics.

Comparing Three Engine Setups: Budget vs Billet Performance

Before directly comparing the Tillotson 225 and Tillotson 236 billet head combinations, it’s important to introduce a third engine into the discussion—the Wildcat 240 Stage 4 build.

The Wildcat 240 represents a budget-friendly performance engine, designed for riders who want solid gains without stepping into a full billet setup. Unlike the Tillotson builds, this engine uses a cast cylinder head along with more basic valvetrain components, including stock push rods and 26 lb single valve springs. It also runs a smaller 24mm carburetor and a milder .268” camshaft.

By comparing all three engines, we can better understand the performance differences between a budget-oriented build and more advanced billet cylinder head combinations used in kart racing and mini bikes.

Engine Specification Comparison

How Does the Tillotson 236 Compare to the Original 225 Test?

When comparing the original Tillotson 225 billet head test to the updated Tillotson 236 combination, the peak numbers alone can be misleading.

Original Tillotson 225 Billet Head

• Peak Torque: 15.5 lb-ft @ 7,100 RPM
• Peak Horsepower: 21.23 HP @ 7,200 RPM

Note: Estimated 22–23 HP without valve float limitations

Updated Tillotson 236 Billet Head

• Peak Torque: 15.7 lb-ft @ 5,800 RPM
• Peak Horsepower: 19.57 HP @ 6,900 RPM

Peak Numbers vs Real-World Performance

At first glance, the 225cc engine appears to outperform the 236cc. It produces slightly less peak torque (only 0.2 lb-ft difference) but delivers approximately 1.6 more horsepower at a higher RPM.

However, peak numbers don’t tell the full story.

When analyzing the entire power curve, the 236cc engine produces more torque—and therefore more usable power—from the start of the pull up to approximately 6,500–6,600 RPM. After that point, the 236 begins to fall off, while the 225 continues to pull stronger into higher RPM ranges

Tillotson 225: Horsepower/Torque - Tillotson 236: Horsepower/Torque - Wildcat 240 Stage 4: Horsepower/Torque

Why the Power Curves Are Different

The primary reason for this difference comes down to camshaft profile and overall engine combination.

The 225cc engine used a larger camshaft (.356 with .462” total lift) and 1.3 ratio rockers. This combination provides:

• More valve lift
• Increased duration
• Greater overlap

These characteristics improve airflow at higher RPM, allowing the engine to “breathe” better as RPM increases. However, they are less effective at lower RPM, where airflow velocity is lower.

Because the 225cc engine has a shorter stroke, it relies more heavily on RPM to achieve higher mean piston speed and improved volumetric efficiency. Around 7,000 RPM (roughly 2,500 feet per minute piston speed), airflow through the head, cam, and valvetrain becomes highly efficient—this is where the engine really comes alive.

On the other hand, the 236cc engine benefits from:

• Increased displacement
• Higher compression
• Greater piston speed at the same RPM

These factors allow the engine to generate stronger cylinder fill earlier in the RPM range.

Combined with the .308 camshaft (.431” lift) and 1.4 ratio rockers, which feature less duration and overlap, the result is:

• Stronger low- and mid-range torque
• Improved throttle response
• Earlier peak torque

This is why the 236cc engine outperforms the 225cc from the beginning of the run up to the mid-range, making it ideal for mini bikes, recreational riding, and kart racing applications that require a broad powerband.

Choosing the Right Setup: High RPM vs Broad Powerband

This comparison highlights a key trade-off in small engine performance:

Tillotson 225 Setup (.356 cam)

• Better for high-RPM racing applications
• Strong top-end horsepower
• Requires higher engagement RPM (clutch or stall)
• Increased stress on valvetrain components

Tillotson 236 Setup (.308 cam)

• Stronger low- and mid-range torque
• More usable, “street-friendly” power delivery
• Better suited for mini bikes and recreational builds
• Broader, more forgiving powerband

Reliability Considerations

Engines designed to make peak power at higher RPM inherently place more stress on internal components—especially the valvetrain. Increased spring pressure, higher lift, and sustained RPM can lead to accelerated wear or failure if not properly supported.

For builds similar to the high-RPM 225cc setup, pushrod selection becomes critical. We recommend upgrading to 1/4” or 5/16” push rods instead of 3/16” chromoly push rods. The larger diameter helps reduce deflection under load, improving valvetrain stability and minimizing the risk of valve float or component failure.

How Does the Wildcat 240 Compare to the Tillotson Billet Head Engines?

Both Tillotson engines used the same billet cylinder head but produced two very different results due to camshaft and valvetrain changes. That raises an important question:

How do these high-end billet combinations compare to a more budget-friendly Wildcat 240 build?

Cost vs Performance: The Real Difference

Before working with Red Beard’s Garage, our goal has always been to develop engine combinations that deliver the best possible performance at the lowest cost, without sacrificing durability. That philosophy started with the Tillotson platforms and continues with the Wildcat series.

One of the biggest barriers for most builders is the cost of a billet cylinder head setup.

A typical MoFlow billet head combination includes:

• Billet cylinder head: $650
• Intake: $75
• Valve cover: $90
• Chromoly pushrods: $30
• Roller rockers: $200

That puts the total at $1,045 before even adding a camshaft, carburetor, or short block.

And that’s just the beginning.

As we’ve discussed in previous builds, once you move into larger camshafts, you also introduce:

• Dual valve springs (requiring proper install height setup)
• Stronger billet rocker arms
• Additional head modifications
• Potential port work and larger valves

These upgrades quickly compound the total cost of a high-RPM performance engine.

The Wildcat 240 Approach: Smarter Performance Gains

Instead of chasing peak numbers with expensive components, we took a different approach with the Wildcat 240 platform—focusing on efficient power gains using simpler, more affordable parts.

The Wildcat 240 Stage 4 build includes:

• Reaper camshaft
• Billet flywheel
• WC200 72mm forged piston with long rod
• CNC-ported WC946-3 cast cylinder head
• PWK24 carburetor

This complete setup comes in at around $1,200 total, which is nearly the same cost as just the billet head setup and valvetrain components used on the Tillotson 236.

Wildcat 240 Performance Numbers

• Peak Torque: 15.71 lb-ft @ 5,400 RPM
• Peak Horsepower: 18.49 HP @ 7,100 RPM
• Head-to-Head Performance Comparison

What makes these results impressive is how closely the Wildcat 240 competes with the billet head engines:

• The Wildcat 240 produces virtually identical peak torque to the Tillotson 236 (15.7 lb-ft), but reaches it 400 RPM sooner, improving low-end responsiveness.
• Peak horsepower is only about 1 HP lower than the 236, and occurs at a very similar RPM.
• Compared to the Tillotson 225 billet head setup, the Wildcat 240 actually produces more torque and power throughout most of the curve up to approximately 6,400 RPM.
• What This Means for Real-World Performance

This comparison highlights a critical takeaway in small engine performance:

You don’t need a billet head to make strong, usable power.

The Wildcat 240 delivers:

• Strong low- and mid-range torque
• Competitive peak performance
• Earlier power delivery
• Lower overall cost

This makes it an excellent choice for:

Mini bikes

• Recreational kart racing
• Builders looking for maximum value per dollar
• Billet vs Budget: Choosing the Right Setup

Tillotson Billet Head Builds

• Higher peak horsepower potential
• Better for high-RPM racing applications
• More expensive and complex
• Requires precise setup and supporting components

Wildcat 240 Stage 4

• Nearly identical torque with earlier delivery
• Strong overall power curve
• Much lower cost of entry
• Simpler, more reliable component combination

While billet cylinder heads and aggressive camshafts can deliver impressive top-end numbers, the Wildcat 240 proves that a well-designed combination of affordable components can achieve comparable real-world performance—especially where it matters most.

For the average rider or builder focused on mini bike performance, kart racing, and small engine reliability, the Wildcat 240 offers one of the best value-to-performance ratios available today.

Performance Comes Down to Application

The performance of these engines ultimately comes down to how and where the power is used.

Most recreational mini bike and kart builds rely on clutches or CVT systems that engage around 2,500–3,000 RPM. While dyno pulls typically begin recording around 3,300 RPM—and become more consistent above 3,500 RPM—this lower RPM range is critical for real-world drivability.

At 3,300 RPM, the differences between these engines are significant:

Tillotson 225 Billet Head

• 6.41 lb-ft torque
• 4.07 HP

*Note: weaker than even a stock Ghost 212 until ~4,200 RPM

Tillotson 236 Billet Head

• 8.76 lb-ft torque
• 5.55 HP

Wildcat 240 Stage 4

• 8.68 lb-ft torque
• 5.92 HP

Low-End Response vs Top-End Power

At lower engagement RPM, the Wildcat 240 clearly stands out. It delivers stronger, more immediate torque, making it noticeably more responsive off the line—an important factor for mini bikes and recreational kart setups.

As RPM increases, the gap begins to narrow:

• The Wildcat maintains a performance advantage up to approximately 6,500 RPM
• Beyond that point, the Tillotson 236 begins to edge ahead slightly
• At higher RPM (approaching 7,000+), the Tillotson 225 becomes the stronger performer due to its more aggressive camshaft and high-RPM efficiency

Racing vs Recreational Setups

In racing applications, clutches are typically set much closer to peak torque—often engaging around 5,000–5,500 RPM or higher.

In this scenario:

• The Wildcat’s low-end advantage becomes less relevant
• The Tillotson 236 offers a slight torque advantage through the mid-range
• The Tillotson 225 ultimately dominates at higher RPM due to superior airflow and camshaft characteristics

This highlights an important principle:

Engine setup is just as important as peak power when matching a build to its application.

Cast Head vs Billet Head Performance

One of the most interesting takeaways from this comparison is how well a cast cylinder head with a mild camshaft can perform when properly matched.

The Wildcat 240 proves that:

• A well-designed cast head
• Moderate lift and duration
• Proper component matching

…can deliver strong, competitive performance without the cost and complexity of a billet setup.

Where Billet Heads Make the Difference

The true advantage of a billet cylinder head comes into play in high-performance and racing environments.

Billet heads are designed to:

• Support higher valve lift
• Handle increased spring pressure
• Provide improved port geometry unrestricted by factory limitations

However, these advantages are only fully realized when paired with:

• Larger camshafts
• Higher RPM operation
• Supporting valvetrain components

Understanding Camshaft and Airflow Differences

At first glance, the difference between the two billet setups may seem small:

• .308 cam with 1.4 rockers
• .356 cam with 1.3 rockers

This results in roughly:

• ~.030” additional lift
• ~10° more duration

But when lift and duration are combined, they significantly increase the total valve event area—which directly impacts airflow. More area under the curve = Greater average airflow ? More high-RPM power

By comparison, the Wildcat 240 operates with:

• Significantly less lift (.163”–.194” less)
• Less duration

Yet it still performs competitively due to its efficient combination and stronger low- to mid-range power delivery.

The Trade-Off: Powerband vs Peak Power

Both the Tillotson 236 and Wildcat 240 could gain more top-end performance with increased camshaft duration. However, this would likely come at the cost of:

• Reduced low-speed torque
• Less responsive throttle behavior
• Narrower powerband

This reinforces the core theme of this comparison:

There is no “best” setup—only the best setup for your application.

Final Thoughts

The Road to Horsepower series continues to provide valuable insight into how different engine combinations perform under real-world conditions. As more dyno testing is completed, these comparisons will help builders make more informed decisions based on their specific needs—whether that’s kart racing, mini bike performance, or a balanced recreational build.

FAQ:

What is the difference between the Tillotson 225 and 236 engines?

The main difference is displacement and power delivery. The 236cc engine produces more low- and mid-range torque due to increased stroke and compression, while the 225cc engine performs better at higher RPM with a more aggressive camshaft.

Is a billet cylinder head worth it for mini bikes?

A billet cylinder head is worth it for high-performance or racing builds where higher RPM, more lift, and increased airflow are needed. However, for most recreational mini bike setups, a well-built cast head can provide similar real-world performance at a much lower cost.

Which engine is best for a mini bike: Tillotson 236 or Wildcat 240?

The Wildcat 240 is often the better choice for mini bikes due to its strong low-end torque, affordability, and broad powerband. The Tillotson 236 is better suited for more aggressive builds that require higher RPM performance.

Why does camshaft selection matter in small engines?

Camshaft selection determines valve timing, lift, and duration, which directly affects where the engine makes power. Smaller cams improve low-end torque and drivability, while larger cams increase high-RPM horsepower.

What makes more power: billet head or cast head?

A billet head has more potential for peak power due to better airflow and the ability to handle larger camshafts. However, a cast head can produce comparable usable power when paired with the right components, especially in lower RPM applications.

Why is low-end torque important for mini bikes?

Mini bikes typically use clutches or CVTs that engage at lower RPM. Strong low-end torque improves acceleration, throttle response, and overall rideability in real-world conditions.

Before addressing that issue, it’s important to understand why the original rules specified a 1-inch bore Tillotson carburetor.

1. The Briggs Animal Limited class served as the reference point for the 208cc Limited Clone class, utilizing 1-inch bore / .900” venturi carburetors. Because the clone platform is a more affordable option, aligning the carburetor specifications makes it easier for racers to transition from the Animal to the Clone. It also simplifies technical inspection, allowing tracks to use the same measuring tools and procedures.

1. Carburetors such as the HL-334WX and HL-304WX (including G and A variants) were originally designed for OHV engines. These carburetors feature a 1-inch bore with a .880” or smaller venturi, which makes blueprinting engines to meet class rules more straightforward and consistent.

1. The 1-inch bore carburetor has long been the traditional standard in Limited Modified classes. The 1.060” bore carburetors were introduced much later, near the end of Briggs’ support for flathead platforms, and were never part of the core foundation of the class.

1. The 1-inch configuration is also the most widely produced size in the Tillotson HL-series, with over 60 years of production history. While not every carburetor is competitive out of the box, this long production run supports the argument that the 1-inch bore is the most accessible and widely available option

• Briggs Flathead (2.437”)

• 1,625 ft/min / 2,437 ft/min / 3,249 ft/min

• Briggs Animal (2.204”)

• 1,469 ft/min / 2,204 ft/min / 2,939 ft/min

• 208cc Clone (2.126”)

• 1,417 ft/min / 2,126 ft/min / 2,835 ft/min

Unlike previous Limited 4-cycle rules, we are introducing a new billet diaphragm carburetor—the XR-25 Intimidator—to replace the traditional cast HL-304WX Tillotson carburetors.

The reasoning behind this shift is simple: the Tillotson HL-series has effectively been phased out. Once Briggs discontinued support for flathead platforms, classes such as Super Stock, Limited Modified, and Open Modified—many of which relied on Tillotson carburetors—gradually disappeared without being replaced by OHV equivalents. As a result, the market for these carburetors declined significantly. While Tillotson has introduced new models for modern 2-cycle engines, those carburetors typically retail in the $300–$500 range in stock form.

Because the original 4-cycle carburetor platform was largely developed by EC Birt, adapting newer carburetors would require entirely new fuel calibrations, revised linkages (and potentially new throttle shafts), and new intake manifolds. This represents a significant amount of additional development work just to offer a suitable “stock” carburetor. The cost of a complete package—including intake, carburetor, and linkage—would increase by approximately $100, with blueprinting adding even more. This directly conflicts with the affordability goals of the class.

Over the past 20 years, we have developed both cast and billet carburetors to replace obsolete 4-cycle platforms. To address the lack of new 1-inch OHV-compatible carburetors, we engineered the XR-25 Intimidator as a direct replacement for the HL-304 series. In support of the class, this carburetor is priced the same as our HL-304WX Dominator, ensuring no additional financial burden for racers.

Now, to address the controversy.

We are generally not in favor of rule changes. However, we have made limited adjustments to better align the performance of Clone and Animal engines, ensuring racers do not feel forced to abandon competitive equipment. In reality, the Clone platform has already displaced the Briggs Animal in many forms of dirt oval racing and is fully capable of sustaining its own Limited Modified class without being combined with other engine platforms.

That said, track and race organizers are often hesitant to eliminate existing classes, and adding new ones can increase logistical complexity. To help ease that transition, we have supported minor rule adjustments to keep the platforms competitive with one another.

The current rule change being proposed by some builders involves increasing the allowable carburetor bore size. The primary motivation is to legalize the use of HL-360 carburetors—originally used on Briggs flathead engines—on Clone platforms. As previously mentioned, the Briggs flathead is no longer supported, and many of its components have become obsolete, often stockpiled by a limited number of builders.

The HL-360D carburetor is not legal in Animal Limited classes and is generally undersized for Open classes. As a result, large quantities of these carburetors remain unused. However, this situation will persist regardless of rule changes, as the entire HL-series has effectively been phased out by Tillotson. From our perspective, the push for this rule change is less about improving class parity and more about creating an outlet for obsolete inventory, rather than adopting carburetors that are purpose-built for the current rules and engine platforms.

We feel obligated to explain why using the HL-360D on an OHV engine is a poor decision. One of the main reasons fewer racers are running Tillotson carburetors today is improper setup—specifically, using carburetors that are not correctly blueprinted for the engine they’re installed on.

Fuel Calibration – Flathead engines require a fundamentally different fuel curve than OHV engines. OHV platforms are significantly more efficient—after all, when was the last time a production automobile used a flathead engine? Because of this, flathead carburetors are much richer on the low-speed circuit. Correcting this for OHV use requires plugging passages beneath the welch plug and redrilling them, which is only one part of properly recalibrating the fuel system.

Additionally, Tillotson diaphragm carburetors are not designed to idle on 4-cycle engines, even though many racers attempt to run them that way. If the low-speed circuit is left in its original flathead configuration, it can create major tuning issues at the track. These include dead spots caused by an overly rich low end, or a lean condition through the midrange and top end. These problems are common and are a key reason why many Open classes avoid diaphragm carburetors altogether. However, when properly set up, a diaphragm carburetor can deliver superior performance.

Throttle Shaft and Linkage – While this is arguably a smaller issue, it is still relevant. The HL-360D and similar carburetors designed for flathead engines pull the throttle shaft from the needle side to avoid exhaust interference. On an OHV Clone engine, this configuration does not align properly. As a result, you will need a linkage conversion kit and, in some cases, a replacement throttle shaft to achieve correct operation. In other words, additional cost and modification are unavoidable.

Intake Manifold – This is another secondary issue, but still important. There are currently no dedicated 1.060” intake manifolds designed specifically for Clone engines. The reason is simple: 1-inch carburetors have historically been the standard for Honda/Clone platforms, dating back to classes like F200, and we have been producing 1-inch Clone carburetors for decades. In contrast, Open Modified engines typically run larger 28mm (1.125”) carburetors.

Taking all of this into account, adapting a 1.060” carburetor to a Clone engine will likely cost $100 or more in additional parts alone. Without a purpose-built intake manifold, you will also need to factor in port matching and full carburetor recalibration, which can add another $150–$200.

In total, you could easily spend $250–$300 modifying a used carburetor just to make it functional in this class. From both a cost and performance standpoint, you are better off purchasing a properly matched HL-304WX—either from an Animal or another Clone setup—than attempting to adapt an HL-360D. At that point, you are also approaching the cost of a brand-new HL-304WX or our all-billet XR-25 Intimidator, both of which are designed specifically for this application.

Now let’s break down the more technical reasons and disadvantages that the HL-360D—or any 1.060” carburetor—has compared to the HL-304WX or our XR-25.

1. Port Velocity and Air Speed

The reason 1.060” carburetors like the HL-360D performed well on flathead engines comes down to airspeed and signal strength. Below is a comparison of stroke and mean piston speed across common platforms:

Engine / Stroke

Piston speed directly influences airspeed through the intake port. Because the flathead has a longer stroke, it generates higher piston speed, which increases air velocity and strengthens the carburetor signal. While increasing port cross-sectional area can increase total airflow (volume), it reduces velocity—which is critical for fuel atomization and throttle response.

When comparing the Clone and Animal, piston speeds are nearly identical. Even at 8000 RPM, the difference is only around 100 ft/min. In contrast, the flathead exceeds the Clone by more than 400 ft/min at 8000 RPM. Even more telling, the flathead at 6000 RPM is within 400 ft/min of the Clone at 8000 RPM. At 4000 RPM—well below racing speeds—the flathead still produces roughly 200 ft/min more than the Clone.

The takeaway is that the flathead generates a stronger airspeed signal to the carburetor, which allows it to tolerate a larger bore with fewer drawbacks.

Looking at it another way, for the Animal to match the flathead’s 8000 RPM piston speed of 3,249 ft/min, it would need to turn approximately 8,849 RPM. The Clone would need to reach roughly 9,170 RPM to achieve the same piston speed.

This highlights the core issue: for a 1.060” carburetor to be truly effective on an OHV Limited engine, it would require significantly higher RPM than these engines are designed to operate within class rules.

While the flathead does not produce the same peak power or torque as OHV platforms, it responds more favorably to larger carburetors due to its higher airspeed. In contrast, the Clone can be negatively affected by reduced port velocity when using an oversized carburetor.

2. CFM and Airflow Demand

The need for higher RPM to match flathead airspeed is only part of the equation. The other limiting factor is airflow (CFM) through the cylinder head.

Class rules inherently restrict airflow, and as RPM increases, the engine’s CFM demand rises accordingly. However, most Clone cylinder heads struggle to exceed 50 CFM at 28” of water at maximum lift. In comparison, carburetors like the HL-360D are capable of flowing nearly double that amount.

If carburetor selection were made without rule constraints, a model like the HL-334WX would be better suited for these engines. It would still exceed the cylinder head’s airflow capacity while maintaining higher intake velocity. This results in a stronger fuel signal, improved atomization, and a broader, more usable power curve.

In contrast, an oversized carburetor reduces velocity without providing a meaningful airflow advantage, since the cylinder head itself becomes the restriction.

3. Tuning Sensitivity and Consistency

As previously mentioned, fuel calibration differs significantly between flathead and OHV engines. However, tuning behavior at the track also varies.

Flathead engines tend to run hotter, and carburetor tuning is often adjusted to manage temperature and prevent overheating. OHV engines, on the other hand, run cooler, yet many racers make the mistake of chasing specific cylinder head temperature targets as a tuning method. This often leads to confusion and inconsistent performance.

These challenges are amplified when the carburetor is not properly matched to the engine. The tuning window becomes narrower as the relationship between the high-speed and low-speed circuits shifts. An engine may perform well on a dyno under controlled conditions, but real-world variables—such as track surface, weather, and race duration—can significantly impact carburetor behavior.

When tuning becomes necessary, an improperly sized or calibrated carburetor can introduce hesitation, dead spots, and inconsistent throttle response—ultimately costing lap time.

We have spent years refining our carburetor designs to minimize these issues. When properly matched and set up, our carburetors typically require little to no adjustment beyond the high-speed needle. In many cases, racers rarely need to make changes at all once properly dialed in.

Our goal extends beyond simply increasing peak power. We focus on improving drivability and tunability—factors that translate directly into faster lap times, greater consistency, and ultimately, better race results.

What’s the Difference Between the HL-304WX Dominator and XR-25 Intimidator?

Since the mid-1980s, EC Birt has been a key developer and importer of Tillotson carburetors in the United States. Carburetors such as the HL-348—and later models like the HL-368 and HL-388, which were based on that platform—were specifically developed by EC for Super Stock, Limited Modified, and F200 classes, all of which utilized 1-inch bore carburetors.

By the late 1990s and early 2000s, the HL-304WX was developed by Carroll Ford, current owner of EC, as a replacement for the HL-348—specifically for OHV engine applications. The HL-304 series proved to be a significant improvement over the earlier designs, offering better overall performance and consistency. Our Dominator versions are arguably among the most refined Tillotson carburetors available for OHV engines, requiring minimal adjustment to achieve optimal performance—allowing many racers to effectively “set it and forget it.”

The XR-25 Intimidator represents the next evolution in that progression. These carburetors were designed to improve upon the original Tillotson architecture in terms of performance, durability, and tunability.

The original X-Series Intimidators were developed as a replacement for the Stage 3+3 “Twilight” carburetors—EC’s highest level of blueprinting and machining applied to Tillotson platforms. Historically, these carburetors ranged from $600 to over $1,000 more than 30 years ago. Even today, 3+3 Twilight versions of the HL-304WX are only available through a select group of builders and are not publicly marketed. The XR-Series builds on that legacy, now produced entirely from billet aluminum.

Manufacturing carburetors from billet provides significantly greater flexibility in design and continuous refinement. Unlike mass-produced cast carburetors—which require large production volumes and slow iteration cycles—billet construction allows for ongoing improvements without those constraints.

Key Improvements of the XR-25 Intimidator

All-Billet Body – As mentioned, the XR-25 features a fully billet-machined body, including the pump plates. The velocity stack is now fully integrated into the carburetor body. Previously, velocity stacks had to be added and carefully machined to blend with the carburetor. This new unibody design improves airflow efficiency while also reducing overall length for better fitment.

All-Billet Pump Plates – The pump plates are fully machined from billet, allowing for improved fuel flow and volume compared to stock cast or modified plates. In general, billet components offer greater precision, consistency, and durability, along with a higher-quality finish.

Throttle Shaft Design – The XR-25 utilizes a slightly larger diameter throttle shaft for increased strength compared to traditional Tillotson designs. Many users have experienced bent or twisted throttle shafts—often due to improper throttle stop setup. To address this, we increased shaft strength while maintaining airflow by thinning the shaft across the butterfly area. Additionally, the revised body design allows for easier repair if damage does occur. Throttle shaft bushings can also be added if needed, further extending service life. The result is a more durable carburetor that is also more serviceable, increasing its long-term value.

Billet Intake Manifold – Changes to the carburetor body required corresponding updates to the intake manifold. As a result, traditional HL-Series intake manifolds are not compatible with the XR-25. While this may initially seem like a drawback, the reality is that the HL-Series platform is being phased out, making a new intake inevitable. Given that this class is still developing—and that the Clone platform represents the future of 4-cycle karting—most racers are already transitioning toward complete, purpose-built carburetor packages.

Proven Performance Components – Carrying over from both the earlier Intimidator Series and our Dominator carburetors are billet steel high- and low-speed needles, along with high-flow red fuel inlet caps. These components have already proven their reliability and performance across multiple platforms.

While the HL-304WX Dominator remains a highly competitive carburetor—and continues to win races—the overall outcome still depends on the complete package: engine builder expertise, driver skill, chassis setup, and tire management.

The XR-25 Intimidator builds on that foundation by incorporating advanced design features and manufacturing techniques typically reserved for much higher-end carburetors. The goal is not just increased performance, but improved consistency, durability, and ease of use.

Perhaps most importantly, the XR-25 delivers these advantages at no additional cost over a standard Dominator carburetor—and at a significantly lower price point than most modern Tillotson offerings.

FAQ

1. What is the best carburetor for a 208cc clone engine?

The best carburetor depends on your class rules and setup, but for most Limited Modified applications, a 1-inch carburetor like the EC Dominator (HL-304WX) or XR-25 Intimidator provides the best balance of airflow, velocity, and tunability.

2. Is a 1.060 carburetor better than a 1-inch carburetor?

Not for most OHV clone engines. While a 1.060” carburetor flows more air, it reduces port velocity and fuel signal, often resulting in worse performance compared to a properly sized 1-inch carburetor.

3. Why do flathead engines use larger carburetors like the HL-360D?

Flathead engines have longer stroke and higher piston speed, which increases air velocity and allows them to utilize larger carburetors more effectively than OHV engines.

4. What is the difference between the EC Dominator and XR-25 Intimidator?

The Dominator is a highly refined cast Tillotson-based carburetor known for consistency and ease of tuning. The XR-25 Intimidator is a fully billet carburetor with improved airflow design, durability, and tunability, offering next-level performance at a similar cost.

5. Do diaphragm carburetors work well on 4-cycle engines?

Yes—when properly calibrated. Diaphragm carburetors can outperform traditional designs, but incorrect setup can lead to tuning issues like hesitation and dead spots.

6. Why is carburetor sizing important in kart racing?

Carburetor size affects air velocity, fuel atomization, and throttle response. Oversized carburetors can reduce performance by weakening the fuel signal and making tuning more difficult.

7. Is the XR-25 Intimidator worth upgrading to?

Yes, especially for racers looking for improved durability, consistency, and performance. Its billet construction and updated design provide advantages over traditional cast carburetors.

8. Can I use an HL-360D on a clone engine?

It is not recommended. The HL-360D requires significant modification, additional cost, and often results in reduced performance compared to carburetors designed specifically for OHV engines.

Most aftermarket performance components for the Honda Clone are designed specifically to improve engine performance for kart racing. These components are typically developed with particular engines and racing classes in mind. For example, camshafts such as the Mod 2 for Cheater Stock, the 255 for the Briggs Animal, 275 lift cams for F200, and the .308/MOD1 for Limited Modified are all designed around specific rule sets and performance goals. Beyond those, most other camshafts tend to fall into either low-lift or high-lift open modified race cams.

A key point often overlooked is that many of these camshaft designs were originally developed for the Briggs Animal engine, not specifically for the Honda Clone platform. While the engines share some similarities, they differ in several important areas such as cylinder head design, bore and stroke dimensions, and piston speeds. These differences affect how a camshaft behaves in each engine.

Because of these differences, a camshaft designed around the Briggs Animal may not always perform optimally in a Honda Clone engine. The way airflow behaves through the head, how quickly the piston moves through the stroke, and how the engine is modified all influence how the camshaft ultimately performs. On top of that, racing class rules dictate what modifications are allowed, which further influences camshaft selection.

In most racing applications, camshafts are designed primarily to maximize performance at higher engine speeds. Even in classes where porting and valve size are restricted, camshaft design tends to prioritize top-end horsepower in order to maximize on-track performance.

However, the reality today is that Honda Clone engines are no longer used strictly for kart racing. The market has diversified significantly over the past 20–25 years. Clone engines are now widely used in minibikes, off-road karts, recreational vehicles, marine applications, and utility vehicles. Even within kart racing itself, the variety of classes and track types has increased dramatically.

Because of this shift, the camshafts available on the market today are not always compatible with the goals of many modern engine builds—especially when combined with the wide range of upgraded components now available.

The Modern Combination Problem

One of the key issues we need to address involves the typical engine combinations being built today.

Many recreational and performance engines are now equipped with carburetors ranging from 22mm to 26mm bore sizes, with 20–24mm venturis. In most cases, these carburetors significantly outflow stock cylinder heads.

However, aftermarket cylinder heads such as the Shredder and Wildcat WC946 have made higher-flowing heads more accessible than ever before. More importantly, these cylinder heads have additional material in critical areas that allow the cross-sectional area of the ports to be increased during porting. This enables significantly higher peak airflow numbers.

While this additional airflow can improve peak horsepower, it can also begin to negatively affect low-speed performance due to lower port velocity—especially when combined with aggressive ignition timing, larger exhaust systems, and larger carburetors.

In many cases, these combinations actually produce less horsepower and torque at lower RPMs compared to milder engine builds such as typical Stage 1 setups with stock cams. When we say lower RPMs, we are generally referring to below approximately 4500 RPM.

For many racing applications, this may not matter because the engines rarely operate below that range. However, in 4-cycle sprint kart racing, it is not uncommon for engine speed to drop as low as 3600 RPM in rpm limited engines, and sometimes even lower depending on track layout.

This creates a situation where an engine that looks impressive on a dyno sheet may actually perform worse on track due to poor low-speed recovery.

The Hot Rod Comparison

The situation is very similar to what happens when someone installs a large, lopey camshaft in a street car or truck.

When installing an aggressive camshaft in an automotive engine, the cam manufacturer will typically recommend installing a torque converter with a higher stall speed. Without doing so, the vehicle may actually lose acceleration and become less responsive at lower engine speeds.

Unfortunately, much of the aftermarket minibike and karting market has focused almost entirely on peak horsepower numbers as the primary indicator of engine performance.

In reality, this often leads to disappointing results for customers.

Just like those large automotive camshafts, engines built with aggressive cam profiles may not perform well unless the entire combination is optimized. Many customers continue using a clutch or torque converter with the factory stall speed of roughly 2200–2500 RPM, while also making no adjustments to gear ratios that could improve acceleration.

As a result, the engine spends a large amount of time operating below the optimal RPM range of the camshaft.

This is one of the main reasons customers sometimes find that their new performance engine is no faster—and occasionally even slower—than their previous setup.

Our Approach: Improving Average Power

One of our primary goals was to improve low-speed performance without sacrificing peak power. Instead of focusing solely on peak horsepower numbers, we focused on improving average power across the usable RPM range.

To achieve this, we designed three camshafts, each offering a different performance focus while maintaining a broad and usable powerband.

Each camshaft emphasizes a particular portion of the RPM range while still maintaining strong performance throughout the rest of the powerband. The goal is to allow engines to accelerate harder while others are still waiting to “get up on the cam.”

During testing, we found that these camshafts were not overly sensitive to minor combination changes and could still produce strong peak numbers when paired with the right cylinder head.

In many cases, we discovered that very little peak horsepower was sacrificed—if any at all. Peak horsepower is largely dictated by the cylinder head’s airflow capability. Instead, our designs helped maintain peak horsepower while significantly improving low-speed torque and average power, and in many cases increasing peak torque as well.

Of course, the exact power output will vary depending on your engine combination, but we work closely with customers to help select the camshaft that best matches their setup.

Reaper

The Reaper camshaft is designed primarily for larger displacement and higher compression engines.

As displacement increases, peak power generally occurs at lower RPMs because a larger cylinder volume requires more airflow to fill. Larger engines can often produce similar horsepower numbers to smaller engines but do so at lower RPMs, while also producing significantly more low-speed torque.

This can be seen in our testing with Red Beard’s Garage, where our milder 236–240cc engines produce similar horsepower but noticeably more torque than heavily modified 212–223cc engines.

The goal of the Reaper camshaft is to move the powerband higher for these larger displacement engines, allowing them to continue pulling strong at higher RPMs.

The Reaper can also help improve top-end power in more restrictive setups, such as engines using stock or near-stock carburetors, or engines with relatively small valves and limited port work.

While the Reaper still maintains a reasonably broad powerband, we generally recommend it for engines primarily set up for racing applications.

Reaper Jr.

At the opposite end of the spectrum is the Reaper Jr.

The Reaper Jr. is an extremely versatile camshaft designed to produce excellent low-speed torque while still improving top-end power over stock or other mild camshafts.

This camshaft responds very well to improvements in cylinder head and carburetor flow.

In more restrictive engine combinations, the Reaper Jr. can increase top-end power while also improving peak horsepower and torque. In engines equipped with higher-flowing cylinder heads featuring larger valves and larger ports, the camshaft helps maintain or even improve low-speed power.

For example, when used in our Wildcat 240 engine with a WC946-3 cylinder head (ported 31/25 valves with 26 lb springs), the Reaper Jr. produces one of the best average power curves from 2500 to 7000 RPM that we have seen.

Throttle response is also noticeably better throughout the power band compared to many camshafts currently available on the market.

Banzai II

The original Banzai camshaft helped start the .265 lift cam revolution. Shortly after its release, nearly every mini bike company began offering their own version of a .265 lift cam.

With the Banzai II, our goal was to further develop that concept while specifically improving low-speed performance.

The new camshaft produces the same peak horsepower—and in some cases slightly more—than the original Banzai, while also improving peak torque and average power across the entire RPM range.

The Banzai II serves as our “when in doubt” camshaft.

It falls directly between the Reaper and Reaper Jr. in terms of overall performance characteristics. While the Reaper Jr. may produce the strongest average power from 2500–7000 RPM, the Banzai II comes very close and can actually outperform it above approximately 3500-4000 RPM.

The Banzai II also produces more top-end power, which makes it a versatile option for applications such as sprint kart racing or recreational engines that spend more time cruising at higher RPMs with a slighly higher clutch stall.

In more restrictive engine combinations, the Banzai II may not make any less power between 2500-3500RPM when compared the Reaper Jr, or stock camshafts or worse losing power compared to bigger camshafts, while still producing stronger top-end performance

Choosing the Right Camshaft

To simplify the selection process:

• Reaper Jr. – Focused on low-speed performance
• Banzai II – Balanced mid-range performance
• Reaper – Focused on top-end power
  

In more restrictive engine combinations—such as those using stock or near-stock valves, ports, and carburetors—low-speed torque is rarely compromised. In these cases, the medium or high-speed camshafts can often be used to help balance power and torque.

However, as the engine combination becomes less restrictive with larger valves, larger ports, and larger carburetors, low-speed power can begin to suffer. In those situations, the lower-speed camshaft profiles help restore balance to the power curve.

Alternatively, a low-speed camshaft can also be used in restrictive combinations to maximize torque, making it ideal for applications such as towing, trail riding, or marine use.

On the other hand, high-speed camshafts are often best suited for highly modified racing engines, particularly in situations where RPM drops are minimal—such as oval track racing.

And if there is any uncertainty, the Banzai II provides a well-balanced compromise that delivers strong performance across a wide RPM range.

Improved Valve Control

Another significant improvement in our camshaft designs involves controlling valve motion at higher engine speeds.

A common issue with many camshafts—particularly many of the .265 lift cams on the market—is valve float occurring between approximately 7000 and 7500 RPM.

This appears to be the result of a combination of valvetrain harmonics and camshaft profile characteristics. Interestingly, once the engine exceeds roughly 7500 RPM, the valvetrain often stabilizes and the engine continues to accelerate normally.

We can clearly observe this behavior both on dyno charts and through air-fuel ratio data. As the valve begins to lose proper sealing, we see a temporary dip in power along with noticeable changes in the air-fuel ratio.

The issue becomes more pronounced as valvetrain weight increases, or when ratio rockers are used to increase valve lift.

One possible explanation is that many camshaft profiles were originally designed around the Briggs Animal engine platform, rather than the Honda Clone. Or, that these cams were designed for less than 7000rpms with a very aggressive profile.

The Reaper, Reaper Jr., and Banzai II camshafts were all specifically designed for the Honda Clone platform, which helps address these valvetrain stability issues.

If you'd like to learn more about each camshaft and see performance data, you can find detailed information on our website using the links listed below.

One of the most common questions we receive revolves around camshafts used in Honda-based clone engines. Builders frequently ask things like:

• What’s the difference between cam cores?

• Which cam fits my engine?

• Do I need to change cams if I install a stroker kit?

• What’s the difference between welded and non-welded cams?

This article breaks down the differences between the most common cam cores, explains where each one works best, and helps you avoid common pitfalls related to engine platforms, part combinations, and performance modifications.

Predator 212 Non-Hemi

We’ll start with the Predator 212 Non-Hemi, because understanding this engine requires understanding why it exists and why it differs from nearly every other Honda-based clone.

The Honda GX series is one of the oldest overhead-valve power equipment engines on the market. As the patents on these designs began to expire, Chinese manufacturers started producing clone engines. Honda faced difficulty enforcing patents overseas, so instead pursued legal action against U.S. retailers—most notably Harbor Freight. Honda ultimately won settlements, but Harbor Freight worked around the patents by making subtle yet significant design changes.

The result was the Predator 212 Non-Hemi, which is arguably the most altered and least interchangeable Honda-style clone ever produced. Many components do not interchange with standard Honda or clone engines, including dowel pin sizes, flywheel taper, and—most importantly—the camshaft core itself.

We cannot stress this enough: the Predator 212 Non-Hemi is the worst platform for performance modifications. Even in stock form, there are multiple engines on the market that are stronger, more durable, and offer better long-term performance potential.

The popularity of the Predator 212 Non-Hemi originally stemmed from its cylinder head design. The non-hemi head used slightly larger valves than a 196cc engine and had aftermarket support—billet rocker arms, valve cover spacers, and billet valve covers were readily available. The valvetrain was lighter and more stable than the hemi variant, making it arguably easier to build for higher RPM combinations.

Early karting rules even allowed builders to pair a Hemi bottom end with a Non-Hemi head to increase compression. The Hemi used a flat-top piston, while the Non-Hemi head had a smaller combustion chamber with more quench area. Those rules have since changed, and newer, more capable engines have entered the market.

The Cam Core Problem

One of the biggest limitations of the Predator 212 Non-Hemi is its unique cam core. The cam journal boss is larger than that of standard Honda and clone engines(Predator 212 Non-Hemi .558" vs .550" for standard Honda/Clones). To our knowledge, it is the only clone engine that uses this specific cam core.

Because of this:

• Camshafts cost more

• Availability is limited

• Many retailers do not stock them

• They are often drop-shipped directly from cam grinders

• Parts do not transfer well to other platforms

When it comes to stroker combinations, this engine becomes even more problematic. While we have developed numerous stroker kits designed for easy installation across many platforms, the Predator 212 Non-Hemi is not one we support. Clearancing issues—particularly around the compression release with 58mm or longer stroke crankshafts—make it labor-intensive and costly.

Labor is the most expensive part of engine building. In many full builds, every component is replaced except the block. Unfortunately, the Predator 212 Non-Hemi block is thin, lacks reinforcement, and is arguably the weakest block on the market. This makes the investment difficult to justify.

Our recommendation is simple: use a platform that accepts the 224 cam core, which the Predator 212 Non-Hemi does not. Doing so saves money, reduces labor, and opens the door to far more performance options.

What Cams Fit the Predator 212 Non-Hemi?

Only camshafts(.558" cam boss) designed specifically for that engine will fit. Parts rarely transfer to other engines, and other engines’ parts rarely fit it. For the same investment, better platforms exist that are easier to build and offer greater performance potential.

Standard Honda-Clone Cam Core

(Also referred to as Hemi, Honda, or Clone)

This cam core fits most original Honda GX-series engines under 200cc and nearly all common clone engines. The cam journal bosses are smaller(.550" cam bosses) than the Predator 212 Non-Hemi(.558" cam bosses) and are far more standardized.

Engines that use this core include:

• 196cc clones (BSP, Ducar, Coleman, etc.)

• Predator 212 Hemi

• Tillotson / Ducar 212

• Tillotson 196R / RS

• Tillotson 212R / RS

• Tillotson 225R / RS

Other engines such as:

• Predator 224 Non-Hemi

• Wildcat 223

• Wildcat 240

• Engines using 58mm or longer stroke crankshafts

can use standard core cams, but require clearancing. The wider counterweights on longer-stroke crankshafts interfere with the compression release mechanism and spring.

We covered this extensively before the 224 core became widely available. While it is possible to clearance the cam or crank yourself, the time involved often outweighs the cost savings. In most cases, it is faster, cleaner, and more reliable to simply use a 224 core camshaft.

For performance builds, starting with one of the platforms listed above simplifies the process dramatically. Stronger blocks, better aftermarket support, and minimal clearancing make these engines far easier to build correctly.

224 Cam Core

(Wildcat 223 / 240, Ducar & Predator 224 Non-Hemi)

The 224 core uses the same cam journals as standard Honda and clone engines(.550" cam bosses), allowing it to fit nearly all of them—except the Predator 212 Non-Hemi.

These cores originated in engines like the Wildcat 223 and Ducar 224 Non-Hemi. The Predator 224 Non-Hemi uses a nearly identical cam, though often with a plastic cam gear.

Key differences between standard and 224 cores include:

• Narrower cam gear (approximately .300" thick vs .316" for standard[196cc/212cc] cam gears

• Narrower compression release (approximately .160" measured from cam gear vs .200" for standard[196cc/212cc] compression release)

• Slightly narrower lobes to clear longer stroke crankshafts and connecting rods (approximately .275" vs .365" standard[196cc/212cc] lobes)

We have progressively transitioned most of our cam offerings to the 224 core. While slightly more expensive, they provide unmatched flexibility. Customers can later upgrade to a stroker crank without replacing the cam or worrying about compression-release clearance.

Clearance concerns with 224 cores are typically related to cam profile and phasing, not the core itself. Higher lift cams often require smaller base circles to maintain clearance. Base circle dimensions vary by manufacturer and cam model, so some clearancing may still be required depending on stroke length and cam selection.

Billet Cam Cores

Billet cam cores are machined from tool steel rather than cast gray iron. They are significantly stronger and harder and are available in both standard clone cores and Predator 212 Non-Hemi cores.

These cams do not use compression releases, eliminating clearance issues entirely. However, they are not compatible with pull-start applications and are intended for high-performance engines using external electric starters. We highly recommend billet cams for engines turning over 8,000 where compression release mechanism could fail.

Welded vs. Non-Welded Camshafts

Non-Welded Cams

Most stock camshafts are made from gray cast iron and rely on heat treatment for durability. These cams are best suited for stock engines or mild builds using single valve springs and low seat pressures.

How to identify a non-welded cam:

• Typically under .285” lift

• Commonly sold on Amazon or eBay

• Usually priced under $75

• No visible weld line on the lobes

On our website, we clearly separate welded and non-welded cams to avoid confusion.

Hard-Welded Cams

Welded cams are machined, slotted, and hard-welded with specialized material to withstand higher spring pressures and RPMs. These cams are more expensive due to material and labor costs.

As a general rule:

• Cams over .300” lift should always be hard-welded

• Some lower-lift welded cams exist, but higher lift demands it

• Visable lines on the lobe of the welding rod material

What Wipes Out a Cam Lobe?

The difference between non-welded and welded camshafts ultimately comes down to their ability to survive higher valve spring pressures and sustained RPM. It is extremely rare to see a properly manufactured welded camshaft wipe out a lobe. Non-welded cams, however, are more susceptible under aggressive conditions. That said, the majority of factors that contribute to cam lobe failure apply to both styles of camshafts. Understanding these factors is critical to building a reliable engine.

Cam Material & Heat Treating

Most non-welded camshafts are manufactured from gray cast iron, which is relatively soft compared to billet or hard-welded materials. While heat treating can improve surface hardness, there is a limit to how hard these cams can be made. In most cases, the heat treatment primarily affects the surface of the lobe. Once that hardened surface begins to wear, material loss accelerates rapidly and lobe failure soon follows.

It is also important to understand that heat treatment consistency can vary, meaning some non-welded cams are inherently more durable than others. This is why following the recommendations of the cam grinder or manufacturer regarding spring pressure, rocker type, RPM limits, and application is critical to preventing premature wear or failure.

Valve Spring Pressure

Valve spring pressure is one of the most common contributors to cam lobe failure. Non-welded camshafts are not recommended for use with dual valve springs or seat pressures exceeding approximately 28 lb. Springs are typically rated by seat pressure at a specified installed height, such as 22 lb or 26 lb. However, actual spring pressure can vary significantly depending on the installed height and retainer configuration.

In addition to seat pressure, spring pressure increases as valve lift increases—commonly referred to as “over the nose” pressure or pressure at maximum lift. This is the primary reason camshafts above roughly .285” lift generally require hard welding. While two camshafts may share the same seat pressure, their over-the-nose pressures can be dramatically different. For example, a .265” lift cam and a .308” lift cam may both use a 26 lb seat pressure spring, yet the .265” cam may see approximately 42 lb at max lift, while the .308” cam may exceed 50 lb. That additional load is transferred directly to the cam lobe and tappet interface.

Rocker Ratio

Increasing rocker ratio introduces another significant variable. Rockers that increase ratio are typically billet rocker arms, which are heavier than stock-style stamped or cast rockers. This added mass, combined with increased valve lift and acceleration, demands higher spring pressure—especially as RPM increases.

A common question we receive is whether billet rocker arms can be used with cams such as our Banzai or similar non-welded profiles. The short answer is no. While seat pressure may remain unchanged, increasing rocker ratio increases valve lift, which in turn raises over-the-nose spring pressure.

For example, using a 26 lb spring with a .265” cam may result in approximately 42 lb at max lift. Adding a 1.2:1 rocker increases valve lift to roughly .318”, pushing over-the-nose pressure beyond 50 lb. At that point, additional spring pressure—or even a dual valve spring—is often required to control valve motion and prevent float at higher RPM.

Our dual “32 lb” springs(approximately .930”), for instance, typically measure around 45 lb of seat pressure at the same installed height as a 26 lb spring (approximately .815”). Due to their higher spring rate, they can reach 70 lb or more over the nose, which is roughly 20 lb higher than a comparable 26 lb spring. As a general rule, non-welded cams should only be used with stock-style rocker arms.

Cylinder Pressure

In small engines, camshaft and valvetrain failures most commonly occur on the exhaust lobe. This is because the exhaust valve begins opening while there is still significant cylinder pressure present. As the valve opens, the camshaft must overcome both valve spring pressure and the remaining combustion pressure in the cylinder.

As compression ratio increases—or ignition timing is advanced, particularly to the point of detonation—the load placed on the exhaust lobe increases substantially. Camshaft design also plays a role. Profiles with longer duration, wider lobe separation angles, or advanced cam timing can cause the exhaust valve to open earlier, when cylinder pressure is still high. This increases stress on the cam lobe and tappet face.

If cam lobe wear is occurring and spring pressure is not the root cause, the next steps should be to reduce ignition timing, lower compression if possible, and increase fuel octane to reduce detonation and peak cylinder pressure.

Oil Selection and Chemistry

Oil is often assumed to be the primary cause of camshaft failure, but it is rarely the sole factor. Stock engines frequently run low-quality oils and still survive because they operate with low spring pressures, low valve lift, conservative timing, and modest compression.

That said, oil can absolutely be either part of the problem or part of the solution. These engines use flat tappet valvetrains, and most modern automotive oils lack the appropriate anti-wear chemistry required for this design. Zinc is commonly referenced in this context, but it is often misunderstood. When discussing zinc, we are actually referring to ZDDP (zinc dialkyldithiophosphate), which functions as an anti-wear additive.

ZDDP levels were reduced in modern oils due to emissions system requirements in newer vehicles that use roller valvetrains. While oil chemistry has evolved to compensate in those applications, flat tappet engines still rely on proper ZDDP activation. Simply adding a zinc additive to standard oil is not an effective solution. In fact, doing so can dilute the oil and interfere with its chemistry, sometimes increasing wear rather than reducing it.

Too little ZDDP can be problematic, but too much can be just as damaging. ZDDP relies on other oil chemistry and requires heat and pressure to properly bond to metal surfaces. Break-in oils are specifically formulated to allow ZDDP to activate quickly during initial camshaft run-in. Adding zinc additives to conventional oil does not replicate this process. Selecting an oil formulated for your specific engine and application will produce far better results.

Lifter and Tappet Replacement

Whenever a camshaft is removed, it is critical that tappets remain in their original locations. Swapping intake and exhaust tappets disrupts established wear patterns and can rapidly accelerate cam lobe wear. Tappets are significantly harder than non-welded cam lobes, and once the cam’s surface hardness is compromised, failure occurs quickly.

When installing a new camshaft, new tappets should always be used, and the engine should be broken in using proper break-in oil and procedures to establish correct wear patterns from the start.

Following these guidelines will significantly improve camshaft durability and overall engine reliability—whether you are using a non-welded, hard-welded, or billet cam core.

But before we get to our evaluation, it’s worth revisiting a recent debate that exposed why a better cast rod is even needed.

Box Stock 196cc Rule Changes: A Quick Recap

Last year, a heated debate erupted over proposed rule changes to the 196cc Box Stock classes, much of it taking place on Bob’s 4Cycle. For years, billet rods were pushed as the solution to the reliability issues of 196cc engines turning 7,000+ RPM. This followed the same pattern the Briggs Flathead classes went through decades earlier moved to billet rods due to stock rod failures.

The problem? Weight and cost.

• Stock Honda-Clone cast rods cost under $10.
• Billet rods are lighter, stronger, and more reliable—but more expensive.
• The rule proposals required billet rods to meet vague weight and dimension requirements that would have forced them heavier than stock cast rods, which made no sense from a technical or performance standpoint.

The debate ultimately highlighted contradictions within the rule-making process and among some builders who had promoted billet rods—until racers pushed back on cost. The conversation narrowed to “lighter cast vs. heavier billet,” ignoring the possibility of better-cast rods or lower-cost billet options, such as non-bearing billet rods. You can find most of the discussion following this link, https://4cycle.com/karting/threads/responding-to-the-latest-cl4-billet-rod-rules.135806/

When we asked professional builders about failure points, they all repeated the same thing Flathead racers learned decades ago:

The rod dipper—not solely the beam—is the primary failure point at high RPM.

Strengthening the dipper would cost very little and dramatically improve reliability. Unfortunately, rule organizations resisted innovation that didn’t fit their established ecosystem. Instead of adopting homologation rules that foster development, they maintained status-quo parts that limit progress, increase controversy, and fragment classes—something we’ve seen firsthand with engines like the Tillotson 196R.

So What Does This Have to Do With the New HD Cast Rod?

This diesel-style HD cast rod initially looked like the exact solution we had been advocating: a reasonably priced, stronger cast rod that could handle higher RPM without jumping to a billet option.

But after receiving and inspecting it, here’s what we found.

The Core Problem: Oil Starvation Risk

The rod uses bearing inserts on both the big and small ends—a great idea in theory for durability. But the big-end bearing has no oil hole. The rod body is drilled, but the bearing itself isn’t.

In an engine platform already known for oiling issues, this is a critical oversight.

Many might argue that bearing clearance allows enough oil flow, but experience says otherwise. We’ve seen too many cast and billet rods fail from oil starvation to gamble on a bearing with no direct oil supply. And you can’t simply swap in ARC or EC bearings—the sizes are incompatible. If the bearing wears out (and it will, without proper oiling), you must replace the entire rod unless you find the matching bearing.

Could you drill the bearing? The wrist-pin bearing sleeve is drilled, but the result shows why that’s risky: the hole was deburred poorly, leaving the bearing surface badly scarred. Damaged bearing surfaces shear oil, increase heat, and accelerate wear. Drilling the big-end bearing risks the same deformation and clearance issues.

And there’s another reason for the lack of oil hole:

These bearings appear to be designed for engines with pressurized oiling systems—not splash lubrication.

Unless you’re running something like a DTV Shredder or a Lifan with pressure-fed oiling, this bearing design is fundamentally incompatible with splash-lubricated GX/Clone-style engines.

Weight: A Deal-Breaker for High-RPM Use

The HD rod features a heavier and more complex beam design meant for diesel engines operating under high compression and high cylinder pressures—not high RPM.

Here’s the weight comparison:

• Stock rod: ~140g
• Billet rod with bearings: 155–158g
• HD cast rod: 182–185g

That makes the HD cast rod:

• 40+ grams heavier than stock, and
• 20+ grams heavier than a billet rod.

That may not sound like much, but in a high-RPM engine, every gram of reciprocating mass multiplies the stress on the crank, piston, and rod. Combine that with a stock-style piston assembly weighing 200–220g or more, and you’re adding significant imbalance and load to an already unbalanced rotating assembly. Most builders already struggle to control vibration—even with lightweight parts—so adding mass only makes things worse. Even more so in stroker assemblies using 58mm, 59mm, or longer stroke crankshafts that increase piston speed.

In other words:

This rod was built for diesel durability, not gasoline performance.

And It Still Doesn’t Fix the Real Problem: The Rod Dipper

Despite being marketed as a heavy-duty design, the HD cast rod does not fix the fatal flaw of the standard cast rod: the dipper.

If you want a stock-style rod to handle 7,000+ RPM, the dipper must be redesigned. This HD rod strengthens the beam—but the beam has never been the weak point on Clone/Predator/Tillotson engines.

This means:

• It’s heavier
• It may suffer from oil starvation
• It still has the same RPM limitation as a stock rod

So the one thing we most needed from a “better cast rod” simply isn’t improved.

Real-World Perspective: What Stock Rods Actually Handle

A well-oiled stock rod can reliably run:

• Up to ~6,200 RPM indefinitely
• Up to ~7,000 RPM intermittently in blueprinted, well-lubricated engines

We see this in LO206, Ghost 212, Wildcat 240, and sealed Predator classes every weekend, running at less than 6200 rpm. So for the HD rod to be useful, it must improve reliability between 6,000–7,000 RPM, not just offer a stronger beam.

As it stands, the HD rod offers no advantage here.

Cost vs. Value: Another Missed Target

The HD rod is about half the price of a billet rod, but three to four times the cost of a stock cast rod. At that price, it must offer meaningful performance value. Bearings alone cost around $20, so reaching parity with stock pricing is unlikely.

And because it introduces new risks (oil starvation, imbalance), the HD rod isn’t attractive for:

• Box Stock 196cc classes
• Limited-mod builds
• Mild performance builds
• Wildcat 240 upgrades
• Or any engine operating in the 6,000–8,000+ RPM range

A billet rod still provides far more performance per dollar.

Expect to See These Rods Online—and Why You Should Avoid Them

You’ll likely start seeing these HD cast rods appear on Amazon and eBay within the next year. We strongly recommend avoiding them. Most of the sellers listing these parts are anonymous resellers who provide no technical support, no product knowledge, and no recourse if a failure occurs. If a problem arises—especially related to the bearing fitment or oiling issues—you’ll be left without any resolution or warranty support.

Final Verdict

The HD cast rod had real potential—on paper. A stronger cast rod with bearing inserts could have been exactly what the 196cc and stock-length Honda/Clone market needed.

But in practice:

• The lack of an oil hole is a fatal flaw
• The weight makes it unsuitable for high-RPM use
• The dipper remains unchanged
• The wrist-pin bearing execution is poor
• The cost doesn’t justify the limited benefits

A billet rod remains the best option for performance and reliability.

We had hoped this HD rod would add value to engines like the Wildcat 240, but as it stands today, it’s not a solution for stock classes or modified builds for recreational or racing uses. Unless the manufacturer addresses these issues—especially the missing oil hole and dipper redesign—it simply can’t compete with existing billet options.

Video Credit Red Beard's Garage

Previously, we upgraded the Wildcat 240 with a forged 72mm piston and an extended connecting rod—yielding solid gains of approximately 0.25 lb-ft in torque and 0.25 hp in peak output. Now, we shift focus to ignition: comparing the stock ignition coil against EC’s PVL CDI ignition paired with an SK300 billet flywheel—but first, the stock setup undergoes testing again under full timing advance.

There were concerns that we weren’t unlocking the full potential of the engine in previous tests, and we wanted to ensure a fair comparison between the standard ignition system and the PVL ignition system. To address this, we decided to test the standard coil setup with a straight-up timing key, which would give us a consistent 34° of total ignition timing.

For full transparency, it’s important to note that most stock ignition coils tend to retard timing under operating conditions. When you observe the timing with a timing light, you'll notice that the ignition timing can drift by 4 to 8 degrees in some cases. This is why many billet flywheels are designed with advanced timing—to compensate for the timing retardation that occurs in stock systems.

Ideally, if ignition timing were fixed(non-retarding) we should see similar results with less aggressive timing. Which is what we expect to see when testing the PVL Ignition coil.

Testing Standard Ignition vs PVL: Unleashing the Engine's Full Potential

1. Ignition Timing Basics: 28° vs. 34°

Starting with the stock coil and flywheel, we tested two timing configurations:

• 28° total ignition timing — using a 6° offset key
• 34° total ignition timing — straight key

Why adjust timing?

• Detonation risk: Increased timing and compression necessitate high-octane fuel (91–93). Too much timing with insufficient fuel quality can lead to blown head gaskets, destroyed pistons, rods, and bearings. If you are having these issues you need to reduce timing, compression and use higher octane fuels
• Kick-back dangers: Advancing timing(firing the spark plug sooner) increases the risk of the flywheel pushing back against the recoil starter—potentially causing sprained shoulders or damaged starters.

Results:

• At 28°, the Wildcat produced 15.46 lb-ft at 5,400 RPM and 17.47 hp at 6,400 RPM.
• At 34°, torque rose to 15.71 lb-ft, and power jumped to 18.49 hp at 7,100 RPM—an increase of 0.25 lb-ft and 1.02 hp. Notably, peak power moved up 700 RPM, and power across the band improved (e.g., 18.25 hp at 6,400 RPM). Ignition tuning clearly matters.

2. PVL Ignition: Dynamic Timing and Performance Stability

Next, we swapped in the PVL CDI ignition with the SK300 billet flywheel. Check out our blogs for the PVL Ignition coil and instructions for the SK300 for more technical information about those products. The test results:

• 27°, 30°, and 33° ignition timing—approximating the standard coil’s 28° and 34° settings.

Performance Outcomes:

• 30°: 15.85 lb-ft torque at 5,200 RPM; 18.31 hp at 7,500 RPM—slightly higher torque 200 RPM sooner, with horsepower 400 RPM later.
• 33°: 15.83 lb-ft at 5,400 RPM; 18.41 hp at 7,500 RPM—virtually equivalent peak performance, with similar usable RPM.
• 27°: 15.77 lb-ft at 5,100 RPM; 18.15 hp at 7,100 RPM—similar to 30° & 33° output but slightly less power and narrower power band.

Conclusion: The PVL ignition delivers consistent power over a broader timing range. This forgiving behavior helps maintain performance while mitigating detonation and kick-back risks.

3. Performance Highlights: Standard Coil vs. PVL Coil

The PVL system may not eclipse the standard coil in absolute peak HP, but it wins in torque delivery and usable power range—especially between 27° and 33°, showing a clear mid-range performance boost.

4. Starting Reliability & Practical Benefits

• The PVL system incorporates automatic timing retard (~20° from static timing, 30 -20 = 10°) below 1,000 RPM, minimizing kick-back during pull starts. As RPM increases, it transitions to full advance—making starts smoother and more consistent.
• It delivers a stronger, faster spark, which:
• Fires more reliably under high cylinder pressures
• Handles richer fuel mixtures better (e.g., during cold starts)
• Improves startup consistency and speed, particularly in colder conditions or with engines that tend to flood easily
• In side-by-side comparisons (video available), the PVL-equipped engine started far more effortlessly, even catching the Red Beard off-guard.

5. Head-to-Head: Wildcat 240 vs. Top Builds

Here’s how the Wildcat compares to other top-performance engines using straight timing keys:

Wildcat 240 Torque & Powerband Advantage vs Predator 224 and Other Top Builds

The Wildcat 240 consistently leads in peak torque across all ignition configurations—whether using 28°–34° timing with the standard coil or 27°–33° with the PVL ignition. This early and strong torque delivery is a direct result of its larger displacement (240cc) and the aggressive Reaper camshaft, which work together to produce superior low-end grunt and broader usable power.

In terms of peak horsepower, all of the top engines tested—including the Wildcat 240, Predator 224 Stage 4, and Tillotson 236R—achieve over 18 horsepower, with less than a 0.75 hp spread between them. These peak figures occur within a tight RPM window between 7,000 and 7,700 RPM.

While the Predator 224 Stage 4 shows a slight edge in peak horsepower—0.25 to 0.44 hp more than the Wildcat 240—the Wildcat counters with 0.7 to 0.84 lb-ft more torque. This torque comes earlier in the RPM band, giving the Wildcat a broader power curve and better acceleration characteristics.

Looking at the RPM spread between peak torque and peak horsepower, the Wildcat 240 enjoys a wider band—100 to 700 RPM broader than its rivals. Reviewing full dyno runs reveals that the Wildcat 240 consistently delivers higher horsepower and torque from 2,000 RPM up to 7,000 RPM, where the Predator 224 reaches its peak. For example:

• At 3,700 RPM, the Predator 224 produces 8.59 lb-ft / 6.17 hp
• The Wildcat 240 at the same RPM range delivers:
• 12.79 lb-ft / 9.15 hp (Standard Coil)
• 12.67 lb-ft / 8.93 hp (PVL Ignition)

This illustrates the Wildcat’s superior low-end and mid-range power, offering a significant performance advantage in real-world driving or racing scenarios.

Additionally, the Wildcat 240 with the PVL ignition setup remains more affordable than the Predator 224 Stage 4 build—making it not only a better value but also a more balanced and versatile engine for both competitive kart racing and high-performance builds.

6. Final Thoughts

• Ignition tuning is critical to unleashing performance. A move from 28° to 34° unlocked noticeable power gains on the Wildcat 240.
• The PVL CDI system offers not only consistent performance across timing ranges but also enhanced drivability and startability—especially under pull-start conditions.
• When compared against similar competitive builds, the Wildcat 240 (especially with PVL ignition) holds its own—delivering standout torque and a stronger overall power curve at a lower cost.

Video Credit Red Beard's Garage

Continuing our Road to Horsepower series, we’re revisiting the Predator 212—now stroked to 223cc—and replacing its ported Hemi head with the Wildcat WC946-3 Non-Hemi cylinder head. This test highlights what kind of power gains you can expect when upgrading to an aftermarket non-hemi head, and why many high-performance builders favor non-hemi designs for reliability and ease of tuning at higher RPMs.

As with most Road to Horsepower builds, our goal is to demonstrate how you can increase engine output using available aftermarket parts while minimizing labor-intensive mods or costly custom work.

Background: The Hemi Build So Far

The Predator Hemi head had already been ported but still used stock-sized valves—27mm intake and 25mm exhaust. Despite the port work and a serious internal build, the limitations of the stock valve sizes and valve float were becoming apparent.

The rest of the engine included:

• 58mm stroker crankshaft (223cc total displacement)
• TM24 flat slide carburetor, tuned by Red Beard
• Ported Hemi head with stainless valves
• Dual valve springs
• 308 camshaft
• 1.2 ratio rockers (~.369" total valve lift)

This setup produced 14.38 ft-lbs at 5200 RPM and 18.18 HP at 7000 RPM—very respectable for a modified Predator-based engine.

Why Swap to the Wildcat WC946-3 Head?

The Wildcat WC946-3 cylinder head offers several advantages over the ported Hemi head:

• Larger 31mm intake valve (vs. 27mm in the Hemi), increasing airflow potential
• Smoother, more stable valvetrain geometry
• More robust aftermarket support for non-hemi parts (valves, rockers, springs)
• Better high-RPM performance and reliability

To install dual springs, Red Beard machined the spring pockets using our valve spring cutter, which is essential for proper spring height and to avoid coil bind at high valve lifts. While the WC946-5 head is pre-machined for dual springs and high lift out of the box, we used the WC946-3 to demonstrate how a builder can still do this work themselves and save money.

Pro tip: If you’re building multiple engines or plan to experiment with cams and spring setups, investing in a spring seat cutter is well worth it.

Performance Gains: Hemi vs. Non-Hemi Dyno Comparison

Key Observations:

• +0.81 ft-lbs torque gain at a higher RPM (5600 vs. 5200)
• +0.25 HP increase, now holding peak power further into the RPM range
• Broader torque curve starting around 3200 RPM, indicating more usable low-end and midrange power
• Smoother power delivery past peak HP, avoiding the steep drop seen with the Hemi head

Also worth noting: The previous Hemi setup experienced a sharp power drop-off after 7000 RPM, which is commonly seen in Hemi heads due to valve float and valvetrain instability at high RPMs.

Why Hemi Heads Struggle at High RPMs

Although Hemi heads have a long-standing reputation for performance, they come with some inherent limitations—especially in small engine builds like the Predator 212.

Hemi Head Advantages:

• Angled Valves: Unshrouds valves for better airflow.
• Straight Ports: Improved flow due to less aggressive port turns.
• Air/Fuel Mixture: Directed more toward the center of the cylinder, improving combustion uniformity.
• Tumble & Swirl: Better mixture motion improves cylinder filling and ignition.

Hemi Head Disadvantages (in small engine builds):

• Limited Piston-to-Valve Clearance: Especially with large cams; can require piston reliefs or custom pistons.
• Combustion Efficiency: Less efficient combustion chamber requires more ignition timing and, in some cases, dual spark plugs.
• Lower Compression: Due to large open chamber; dome pistons are often needed to raise compression.
• Valvetrain Limitations:
• Difficult to achieve proper valve spring install height without cutting into ports.
• Fixed rocker geometry limits valve lift and spring selection.
• Pushrod angle is less favorable, increasing flex and contributing to early valve float.

These issues compound as RPMs rise, making Hemi heads more prone to mechanical instability, even with upgraded parts.

Why Non-Hemi Heads Are Often Preferred

While the flow characteristics of a Hemi head are impressive, non-hemi heads like the WC946-3 offer:

• Better valvetrain geometry: Easier to set up for high lift and high RPM without pushrod or rocker arm issues.
• Greater aftermarket support: More valve sizes, rocker styles, and spring combinations available.
• Tighter combustion chambers: More efficient burn and higher compression with flat-top or mildly domed pistons.
• Less valve float: More stable at higher RPMs, even under heavier spring loads.

So Which One is Better?

It depends on your application:

• For stock or near-stock classes, the Hemi head usually makes slightly more torque and top-end when valve float and lift aren’t a concern. It’s a great option for mild builds or classes where head work is limited.
• For serious performance builds, especially those revving over 7000 RPM, the non-hemi head is usually the better choice. The valvetrain is more stable, easier to tune, and can accommodate higher lift cams without major modification.

Final Thoughts

This test clearly shows that upgrading from a ported Hemi head to an aftermarket non-hemi head like the Wildcat WC946-3 can deliver:

• More torque across the full RPM range
• Higher peak horsepower
• Improved power retention past 7000 RPM
• Reduced risk of valve float and mechanical failure

If you’re building a high-revving Predator 212 or 223cc stroker, the non-hemi head offers more flexibility, better reliability, and more potential for future upgrades.

Reminder: By the time you fully build out a Predator Hemi, nearly every original component is replaced. If you’re planning a serious build, it’s often smarter to start with a platform that has a stronger block and larger displacement potential. We highly recommend our 223 or better our 240 which comes with many advantages and can make more power and torque for less.

Video Credit Red Beard's Garage

In the last 240 build, we left off with the WC22 carburetor, Banzai 265 cam, and a hand-ported WC946 cylinder head. Since then, we have started producing a CNC-ported version of the same Wildcat cylinder, designated as WC946-3. This version features the same 26 lbs springs, stainless steel 31/25 valves, and billet retainers. Our goal was to generate a significant amount of power without the need for expensive cylinder head modifications, billet rockers, chromoly push rods, and hard-welded cams. Instead, we aimed for a combination that would be easy to assemble at a low cost while still achieving high power output.

We have made several changes to the setup compared to the previous version. These changes include the type of head (switched from hand ported to CNC), the carburetors (replaced WC22 with PW24), and the camshafts (changed from Banzai to Reaper). Additionally, we have made some tuning adjustments.

In terms of power and performance, the two combinations may appear very similar when only considering the peak power figures. However, there are notable differences when we examine the complete dyno run.

Camshafts: Banzai Vs Reaper

The Banzai camshaft has arguably been one of the most popular .265 lift camshafts on the market, prompting many other retailers to offer their own versions of a 265 cam. Most of these alternatives are based on the Dynocams CM-Grind. While the Banzai camshaft performs exceptionally well for racing purposes, a comparison of the dyno results reveals that the Reaper camshaft significantly improves in several areas.

What inspired the development of the Reaper Cam?

We began our analysis by examining spec racing engines such as the Briggs Lo206, Ghost 212, and the Tillotson 225RS. The Briggs and Ghost engines are quite similar in specifications and power output, excelling at low-speed power production. In fact, the Ghost 212 demonstrated impressive performance on the dyno, showing better results than most engines tested by Red Beard between 3200 and 4000 RPM.

Both the Briggs Lo206 and Ghost 212 engines engage their clutches between 3400 and 3600 RPM and can operate up to 6100 RPM, providing a 2500 RPM operating range. These engines exhibit a fairly linear power band, peaking around 5100 RPM.

Originally, the Tillotson 225RS had its RPM limit extended by only 400 RPM; however, its clutch needed to engage between 3800 and 4200 RPM because it utilizes a .265 lift camshaft, which shifts the peak torque to a higher part of the power band. To better accommodate this camshaft, the Gen 2 engine was increased to 7500 RPM.

The Tillotson shares characteristics with many engines on the market, particularly when employing a 265 lift cam and a VM22/PZ26 carburetor. If the Tillotson, Ghost, and Briggs all have the same gear ratio and engage their clutches between 3400 and 3600 RPM, the Ghost and Briggs will out-accelerate the Tillotson and many higher horsepower builds for the initial 500-800 RPM. While this may not seem significant, it is a notable difference from typical setups.

In non-racing or recreational applications, stock torque converters and clutches engage at lower RPMs, around 2200-2500 RPM. This is significantly lower than what Red Beard tests, as the disc clutch used engages around 3200 RPM, which is relatively low for a disc clutch.

At 3300 RPM, the Ghost produces 5.8 ft-lbs of torque, the Wildcat 240 with the Banzai outputs 3.13 ft-lbs, and the Reaper yields 9.83 ft-lbs. This means the Reaper generates more than three times the torque of the Banzai at 3300 RPM and nearly double that of the Ghost. Keep in mind that the power figures will be less at 2500 RPM. The Stage 4 Wildcat likely produces a torque value at 2500 RPM comparable to, or possibly exceeding, that of the Briggs, Ghost, or Tillotson at their recommended clutch engagement RPMs, making it much more suitable for aftermarket recreational use due to its broader RPM range.

In addition to producing more power across the board, this engine configuration offers more versatile gearing.

To illustrate this:

If you use the same 6:1 gear ratio at 3300 RPM, the torque figures yield 34.8 ft-lbs for the Ghost, 18.78 ft-lbs for the Banzai Stage 1, and 58.98 ft-lbs for the Reaper. The Reaper's higher and more stable RPM range allows for increased gear ratios to obtain additional torque, or, conversely, a reduction in ratio for higher speeds.

Here are the goals for the Reaper camshafts:

1. Achieve the best average power between 3500 and 7500 RPM.

2. Generate more torque below 4000 RPM than a stock or mild engine.

3. Provide strong acceleration when engaging the clutch at 2500 RPM.

4. Produce as much or more power than a typical stage three build using a standard 265 camshaft.

What changed in engine tuning?

The camshaft has performed well; however, a slight adjustment in tuning may have affected the engine's overall output. We reduced the ignition timing from 34° to 28°. The 240RS has a compression ratio of approximately 11.5:1, which is quite high for pump gas. We've experienced issues like detonation and blown head gaskets with fuels rated below 90 octane. To address these problems and help the engine run cooler, we decided to pull timing. Although this adjustment may lead to increased power output, it's important to remember that maximizing power isn't always the goal, especially when the gains are not worth the potential decrease in engine longevity.

Additionally, the carburetor is running slightly richer, particularly with a significant dip in performance from 3800 to 5200 RPM and again above 7000 RPM. Using a smaller main jet could resolve the dip at low RPMs and lean the mixture at higher RPMs, allowing the engine to produce more peak horsepower. In our testing, carburetors tend to run a bit richer in non-karting applications.

For racing go-karts, fuel is drawn from a tank located between the driver's legs, traveling through approximately 2.5 feet of tubing to the fuel pump and then to the carburetor. In gravity-fed applications, commonly seen in mini bikes and various recreational vehicles, the fuel tank is positioned much closer, which may provide additional pressure from the weight of the fuel. This can lead to greater fuel flow compared to the setup in a racing go-kart.

We recommend purchasing a set of jets when buying a carburetor and suggest going down at least one jet size for gravity-fed applications compared to the jet that comes with our carburetors. Keep in mind that tuning can vary due to atmospheric conditions. For more detailed tuning instructions, please refer to our blog section or the product description.

Carburetors WC22 vs PWK 24

In the testing conducted so far, there is little difference in peak power and torque between the two carburetors. The WC22 features a 26mm bore with an oval venturi measuring approximately 23mm by 20mm, flowing about 85 CFM. In contrast, the PWK24 has a 24mm bore with a 23mm diameter venturi that flows about 107 CFM. On the flow bench, the head demonstrates a flow rate very close to 85 CFM at .250 lift; however, the camshaft only allows for about .265 lift, which is not enough to fully utilize the potential of these carburetors at this stage.

Flat Slide or D-shaped slides are expected to atomize fuel better, provide more responsiveness, and generally yield more power, but the overall performance depends significantly on how well the carburetor is tuned for the engine. The PWK is likely to produce slightly more power once the jetting is properly adjusted; however, the WC22 has proven to be very capable of delivering identical power output.

How Does the Wildcat 240 Compare to Other Engines?

The comparison is not straightforward, as many may expect significant power gains in peak torque and peak power. While peak numbers did improve, the results may seem underwhelming to some. This can be attributed to our camshaft design, which focuses on broad power delivery rather than peak power. Although we could have designed a camshaft to favor higher peak numbers, we believe that while many cams on the market can achieve that, very few can produce power effectively in the 2500-4000 RPM range like the Reaper cam, while still delivering similar peak power between 5000-7500 RPM.

Here are some recent tests and comparisons with similar output engines:

The Wildcat 240 Stage 4 ranks as the fifth-highest-horsepower engine, excluding billet heads, and second in peak torque. Our Tillotson 236 kit, combined with the Banzai and WC22 carburetor, ranks second in horsepower and first in torque, securing the best overall performance.

The most intriguing comparison is between the Wildcat 223 and 240, both utilizing the new Reaper cam, CNC-ported head, and PWK24 carburetors. The key differences are in compression, displacement, and ignition timing. The Wildcat 223 produced about three-quarters of a horsepower more, but did so at 1300 RPM higher. Conversely, the Wildcat 240 generated 1.25 ft-lbs more torque and achieved this 1200 RPM sooner. The lack of top-end power in the 240 may be due to reduced ignition timing or the engine's dynamic characteristics, highlighting the importance of testing since not every setup is one-size-fits-all, and proper tuning is vital to maximize the performance of any combination.

The Predator engines represent a more advanced level of assembly, featuring higher lift, larger cams, and ratio rockers, which help achieve higher peak numbers in some cases. Combining the WC946-3 with either the PWK24 or WC22 carburetors and either the Banzai or Reaper cams in the Wildcat 223/240 or Tillotson 228/236 models positions these engines on par with the higher-performing builds. It's worth noting that we have yet to reach the full potential of these Wildcat builds.

Understanding Proper Ventilation for High-Performance Small Engines

When building or tuning high-performance engines—whether for racing go-karts, mini bikes, or performance mowers—crankcase venting is often one of the most misunderstood and overlooked systems. But it plays a critical role in maintaining engine efficiency, durability, and reliability. This article will explain how crankcase ventilation works, the purpose of a PCV (Positive Crankcase Ventilation) valve, and how to properly set up your system for your engine build.

What Is Crankcase Pressure?

During engine operation, combustion gases can leak past the piston rings into the crankcase—a phenomenon known as blow-by. These gases increase internal pressure inside the engine block. If this pressure isn’t properly controlled, it can cause:

• Oil leaks from seals and gaskets
• Aerated or foaming oil, reducing lubrication quality
• Reduced horsepower due to internal drag
• Oil contamination from fuel and combustion gases

Crankcase Venting: Why It's Important

The solution is to vent the crankcase, allowing pressure to escape and preventing buildup. But it’s not enough to just vent—it needs to be done properly and directionally.

Basic Vent (Open Venting)

An open vent—like a hose or fitting—is the simplest form of crankcase ventilation. But these are bi-directional. That means while pressure can escape, air can also be sucked back in when the piston moves down. This reintroduces moisture and contaminants, destabilizing crankcase pressure.

PCV Systems: The Smart Way to Control Pressure

A Positive Crankcase Ventilation (PCV) valve is a one-way check valve that only allows gases to flow out of the crankcase. It helps maintain a controlled vacuum or positive pressure, depending on how it's routed.

Benefits of a Proper PCV System:

• Keeps air moving one way only
• Reduces oil contamination
• Prevents pressure spikes
• Maintains ring seal under load
• Controls oil mist and blow-by

Race Engine Application: More Than Just Emissions

In automotive engines, PCV systems were introduced as part of the emissions control system. In racing engines, however, a proper PCV setup is crucial for both performance and longevity.

For example:

• Methanol engines create more moisture in the crankcase, which must be vented effectively.
• High-RPM engines build pressure fast, so directional flow control is essential to avoid oil push-out.

How to Set Up a Proper Venting System

1. Use a One-Way PCV Valve

Avoid using open fittings. Install a billet PCV valve (like EC’s 280, 281 & 282) in a high location—like a valve cover or side cover—with a check valve built in.

2. Route to a Catch Can (Optional but Recommended)

Instead of venting to the atmosphere, route the PCV hose to a catch can to trap oil mist and vapor. Race tracks and organizations usually require catch cans.

3. Avoid Cross Venting

If you're using multiple vents, make sure they don’t cancel each other out. For example, two open vents can allow air to flow in and out simultaneously—defeating the purpose.

4. Use Proper Hose Diameter

A vent hose that’s too small will restrict airflow. Use at least 1/2” ID hose when using EC’s PCV.

Common Mistakes

• Using an open barb fitting instead of a check valve
• Blocking vents entirely
• Routing PCV below oil level, which can suck oil into the valve or catch can
• Over-venting: more holes, better airflow, is useless if the direction isn't controlled

Recommended Products

• EC 280 Billet 3/4”-10 PCV Valve
  Designed for EC Clone side covers
• EC 281 Billet 3/4”-16 PCV Valve
  Designed for Briggs Flathead Burris side covers
• EC 282 Universal Billet PCV Valve
  Design with two 1/2 barb to fit various applications
• EC Catch Can Kit
  Keeps oil mist off the chassis and your shoes
• Valve Cover Breather Kits
  For Tillotson, Predator, or Honda clones

Final Thoughts

Crankcase ventilation may not be as glamorous as cams and carburetors, but it’s one of the easiest and most effective ways to increase your engine's reliability and efficiency. Whether you’re running gas or methanol, stock or open class—you need to control crankcase pressure, not just relieve it.

Don’t just vent. Vent with purpose.