EC's EGO Disc Clutch Explained

What is the EGO Clutch?

Features

- Advanced multi-disc clutch design specifically for karting and small engine racing

- Fully CNC machined billet steel and aluminum components

- Six adjustable springs and levers for precise rpm engagement.

- Proprietary friction material is designed for smooth, consistent engagements.

How does it work?

The purpose of any clutch is to transfer power from the engine to the drive train. In the context of karting or small-engine racing, how that power is being transferred improves on-track performance. 

The goal in karting or small engine racing is to have the clutch engage and transfer power to optimize acceleration. It does this by slipping until the maximum torque can be transferred without bogging the engine or spinning the tires. Optimal acceleration is a balance between bogging and spinning, and the Ego clutch does a great job of mitigating that in its design and setup. 

Before we set up the EGO, we need to cover the reasons for using it and compare it to other style clutches.

What's the difference between a shoe or drum clutch and a disc clutch?

Both utilize centrifugal forces to engage the clutch, but the method is different between the two clutches. 

A shoe or drum clutch uses three primary components to set the engagement: shoes, weights, and spring tension. Different brand clutches use sets of color springs with different tensions, either light or heavy shoes or weights that can be inserted to set the engagement. The heavier the shoes, the heavier the weights, and the lighter the spring tension, the lower the rpm when engaging the clutch. 

A disc clutch uses a set of springs that can be adjusted by changing the install height, much like your valve springs. The lower the install height, the higher the spring tension or pressure. Instead of shoes, the disc clutch uses levers to push the pressure plate to engage the friction discs. The dimension of the lever and the ability to add a bolt and nut to increase the lever weight will change how quickly the clutch engages; just like the shoe clutch, the higher the spring install height, which lowers the spring pressure/tension and the heavy the weight of the levers will engage the clutch at lower rpms. 

The other significant difference is the friction material, surface area, and weight. 

A shoe/drum clutch uses the surface area of the shoes as the contact point. In many cases, you are not using the total area of the shoe but as low as 50% of the shoe's surface to make contact with the drum. 

Here are some approximate surface areas of popular shoe/drum clutches used for kart racing

Hillard Fury – 8.24 squared-inches friction surface area

Hillard Flame – 6.36 squared-inches friction surface area

Noram Stinger – 7.25 squared-inches friction surface area

The disc clutch has an area of 3.39 square on each side of the friction disc, or 6.78 square per disc, and will use 100% of the friction material's area unless the clutch is damaged. 

1-Disc – 6.78 squared-inches friction surface area

2-Disc – 13.56 squared-inches friction surface area

3-Disc – 20.34 squared-inches friction surface area

4-Disc – 27.12 squared-inches friction surface area

The disc clutch's surface area for its weight and size makes it much more effective. A drum clutch has almost the same friction area as a 1-disc clutch, which means that every disc is like having an additional drum clutch; i.e., a 2-disc is the same as having two drum clutches. If adding more than one clutch is possible, you would double the weight and increase parasitic losses. In other words, the disc clutch can handle more power while weighing less. 

What is the horsepower or torque rating of each clutch?

Since dynos are so radically different, with as much as 40% difference, it isn't easy to give each clutch a power rating, but in general, each disc can handle 8-12hp.

1-Disc – Briggs LO206, Ghost 212, Stage 1, and some Stage 2 Builds

2-Disc – Briggs World Formula, Tillotson 225/228, most Stage 3 and Stage 4 builds.

3-Disc – Highly Modified Engines with ¾ output shafts. 

4-Disc – 1-inch Output shafts: while we rate each disc to handle between 8-12hp per disc, the 4-disc has been used on engines making well over 60hp, and as we said, there can be a 40% difference in dynos, some engines claiming over 80hp. 

Other factors impact how much power a disc clutch can handle. The setup and the vehicle often cause premature wear or damage to the clutch. 

Are these clutches suitable for recreational builds?

The short answer is no, but it depends on how the clutch is used. The following information will cover troubleshooting, which will help you choose a clutch for your application and prevent or resolve clutch-related issues. 

Slippage is the number one problem with any drive train setup, whether a clutch or CVT/torque converter. A clutch will be the shoes or disc; for most CVTs, it will be the belt. 

-Horsepower/Torque—the more power you make, the more surface area you'll need for the clutch to engage without slipping, but there is more to it. 

- Weight/Load: The other side is the weight or load of the vehicle. In videos with the Stage 3 Wildcat or Super Ghost 223, the Super 30/Juggernaut CVT slips more with Red Beard than with Lonnie. The reason is the weight and load on the bike. With a lighter load, the Super 30 had no trouble with the power from the Wildcat or Super Ghost builds. The same would happen with a clutch, but instead of slipping the belt, it would be the shoes or disc slipping. One way is to increase the surface area of the clutch by going from a 2-disc to a 3-disc. But that's not the only way to reduce slippage.

- Gear Ratio/Tire Size – A Super 30 CVT helps because of its variable gear ratio; however, Red Beard recommends a final gear ratio of 6:1 to prevent the belt from slipping. With any clutch or CVT, the gear ratio multiplies the torque to the rear axle, even though the engine torque remains the same. A higher gear ratio (6:1 vs 5:1) will increase torque and acceleration. It allows the engine to move a heavier load or weight. The torque at the crank differs from the torque at the axle or tire. Because the bike isn't accelerating, it puts more strain on the belt or chain. The engine itself isn't underpowered; in fact, its power is overcoming the belt's grip. If you are using a clutch and a chain, the chain is much more robust, so the clutch slips because the engine is overpowering the friction material. Since a clutch only allows one ratio, you must balance low-speed acceleration and top-end mph. The tire size also affects the ratio; a larger tire will want a higher gear ratio, and a smaller tire will allow a smaller gear ratio. Just keep that in mind: if you upgrade the tires on your bike, you may need to make a gear change to maintain its acceleration and mph. Your gear ratio multiplies the torque applied to the rear axle, which is then transferred by the tires. Taller tires and lower gear ratios can increase the load on the engine and clutch.

- Grip Level—The pattern of tread or compound can change the tire's grip, affecting handling and the engine's load. There is a big difference between hard hooking vs. spinning tires or low-speed cornering/drag racing from a dig vs. high-speed cornering/roll racing. The more grip and less momentum, the greater the load. 

Kart Chassis Handling—If the chassis is ill-handling, binding, or locked down, this increases the load on the engine. Often, racers blame the engine when it's the chassis handling that causes parasitic losses that reduce acceleration and sometimes top-end speed. In those cases, the clutch may prematurely wear or struggle with handling the load.

Now that we've covered some concepts for clutch selection, would we recommend the Ego for recreational usage? It depends. Trail riding, street cruising, and racing have different variables and demands. We wanted to cover our concepts first because if you have an issue with your current setup, having a more expensive clutch doesn't mean it costs guarantees to resolve your problem. 

Trail riding – A CVT is hard to beat in almost any situation, but because you are not running at a high mph, having the extra low end helps you get around the trails with rough terrain, obstacles, and hills. Most engagement will be set between 2000-2800rpms

Street Crusing—Again, a CVT that allows you to accelerate but offers good mph, thanks to its variable ratio, makes cruising more enjoyable. If you insist on using an EGO clutch, you'll want to engage at much lower than peak torque. Since you may not have much load on the bike and you're not optimizing the setup for racing, it's possible to use the Ego successfully.

Most engagements will be set between 2200 and 3600rpms, which primarily depends on the engine's power/rpm range and your cruising speed. You don't want the clutch to slip at your cruising speed. For example, if you plan to cruise at 5 or 25mph, ensure the gear ratio works out so the clutch doesn't slip by lowering the engagement or raising the gear ratio. 

Racing—The EGO's true intention is for racing applications. The clutch shines because of the convenience of the engagement tuning, which can be swapped and calibrated for different applications and tracks. 

Where should the clutch be set up for engagement?

The rule of thumb has been 200-300rpms above peak torque. However, there are exceptions to this rule depending on the class, overall weight, gearing, etc. And unless you have a dyno, it may be difficult to know where your engine's torque peaks.

First, let's familiarize you with clutch engagement by comparing it to the clutches in your car or truck. 

Dropping the clutch vs easing into the clutch– If you have ever dropped it or engaged it rapidly, it can do one or two things depending on the rpm. If the rpms are low, you can stall the engine or have a slow, stuttering acceleration. If the rpms are high, you can spin the tires not solely because of the power or torque of the engine but because of the engine's speed and inertia. Neither of these helps acceleration and is hard on the driveline. Instead, you want a smooth clutch engagement, just like in your car. You want the rpms to stabilize or gradually increase as the clutch engages until it's fully locked, and in most cases, that's about a 300rpm range. 

You can shorten the engagement of the clutch by adding weight to the levers, which helps the clutch hit harder. Usually, there will be some overlap in the clutch engagement between the lever and the lever with the bolt and nut added. If you are set up correctly but feel as if you need the clutch to come in harder without bogging or spinning the tires, add the bolt and nut and change the installation height of the spring. Even with a hard-hitting setup, the EGO is designed to offer a smoother engagement to reduce bog during acceleration. 

Today's OHV engines produce more low-end power with a broader powerband. If you look through past videos, many engines never make less torque than they did stock; even at 3000rpms, torque increases typically, and with engines like the 223/224 engines, the torque from 3000rpms to peak can be less than 1-ft/lbs difference. The OHV engines are much more forgiving than the flatheads and two-cycle engines, which not only helps the clutch perform better but improves its durability by allowing it to be engaged at a lower rpm. 

In some cases, peak torque could be 5000+ rpms, which, with really high engine speeds, can cause the wheels to spin. In a way, you can use your clutch as traction control by engaging it at lower rpms. The other problem with high rpm engagement is that when you have high levels of grip or heavier loads, the clutch can slip too much, causing wear or breaking chains. 

How do you set up the clutch without a dyno?

EC's Ego clutch has guidelines for where you want the clutch to engage. However, these are only guidelines and factors outside the engine's performance can influence where the clutch engagement is optimized. In most cases, circuit racing is used, such as road racing and sprint for 4-cycle karting. Setting the clutch lower than the guideline by as much as 1000 rpms would be fine. If the clutch is set to engage high, it can cause the clutch to slip too much, and you can burn up the clutch. Rpms that are too low, the engine may not accelerate like you want, but you lower the risk of damaging the clutch. You'll want to focus on the engagement for your slowest corner, like a hairpin, especially ones that follow a high-speed section where you are slowing down to make a tight corner, and the engine speeds will be very low. Come in and gradually increase the install height of the spring to about .015 at a time(ensure all the springs are equal), which should be about 200rpms. Do this until you get the acceleration you want when raising the engagement no longer improves acceleration. 

To get the most from this technique, we recommend using data acquisition like the Alfano 6, which can download data to your phone, tablet, or computer. Measured and recorded data will be more accurate than feeling it by the seat of your pants, especially if you are tuning for another driver. In some cases, engaging the clutch at or above peak torque may not provide a substantial advantage. The key is to slip the clutch to keep the rpms up for fast acceleration. Still, keeping the rpm engagement lower and reducing the slipping of the clutch without sacrificing acceleration will improve its durability.

Like any "racing" component, the techniques use to optimize the component are just a crucial as the component itself. The EGO clutch provides some of the best technology available for kart racing clutches, but using it correctly is the key to its advantage.