Predator 212 Road to Horsepower: Hemi vs. Non-Hemi Cylinder Head Showdown

Predator 212 Road to Horsepower: Hemi vs. Non-Hemi Cylinder Head Comparison

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.