Picking the right clutch for your Corvette can be confusing. Do you buy the one with the biggest price tag? The highest performance level? While it might seem logical at first, this kind of thinking is liable to leave you with a clutch that doesn't suit your driving style, or one that won't hold the power your car is producing. What follows is a guide to help you choose the correct clutch and pressure plate for your application.
Most clutch companies offer a variety of clutch materials and pressure plates, as well as twin-disc setups. Each type is designed for a specific use and has its own set of pros and cons. So, how do you determine which one is right for you? First, we'll need to brush up on basic clutch tech.
The clutch is, in simple terms, the link that mates the engine to transmission. When engaged (no pressure on the pedal), the clutch allows torque to be transferred through the drivetrain. When the pedal is depressed, it disengages the engine from the transmission, stopping the torque transfer.
Let's take a look at the components that make the clutch system work, beginning with the pressure plate. The pressure plate applies clamping force to the clutch disc, causing it to be squeezed between the plate and the flywheel. This effect occurs when you release the pedal. When you depress the pedal, the pressure plate releases its grip on the disc, and the torque from the engine is no longer transmitted to the transmission.
The pressure plate contains a couple of very important parts. When it comes to holding power, the diaphragm springs are critical. Simply put, the more diaphragm pressure there is, the more clamping force the plate will have. The biggest downside is that higher spring pressures typically require more muscle to depress the clutch pedal. Other drawbacks to a lot of diaphragm pressure include more stress and higher loads on the linkage and thrust bearings.
The second area of importance for clamping force involves the fulcrum points. By changing the fulcrum points, the laws of leverage may be used to create more clamping force. Although this approach doesn't result in the adverse effects that changing the diaphragm pressure does, it does have its own drawbacks. A mushy-feeling clutch pedal, longer pedal travel, and quicker disc wear can all occur.
Now that we've learned some pressure-plate basics, let's talk about the clutch disc. The disc is located between the pressure plate and the flywheel, so you can think of it as the salami between the two slices of bread. The purpose of the disc is to allow a smoother transfer of power from the engine to transmission.
Most discs are made with a sprung hub, which is designed to absorb some of the rotational force when the clutch is first engaged. Almost all street-oriented performance discs have sprung hubs, though some manufacturers do offer solid-hub discs. A solid hub is stronger but sacrifices driveability.
The Marcel is the thin slice of material between the clutch facing and the hub. It's designed to act like a cushion, giving a small amount of dampening when the clutch is first engaged. Again, it's all about driveability.
The last and-and, when it comes to performance, the most important-part of the disc is the clutch facing. The type of facing material used has a tremendous effect on the overall torque capacity of the clutch system. We'll discuss some of these materials and their respective benefits in a just a moment.
The flywheel serves as one of the two mating areas for the clutch disc, the other being the pressure plate. It also provides a place to mount the pressure plate and, in most applications, the starter ring gear. When replacing the clutch, you'll need to have the flywheel resurfaced or replaced as well. This will prevent premature wear and ensure optimum clutch-to-flywheel grip.
Up until now, we've looked at the car and the way it's driven. Now, let's look at the different clutch materials and how we use the information to pick the right package.
Most stock Corvette clutches are made up of a standard pressure plate and an organic disc. These are great for silky-smooth driving but not so great for holding power. If you don't have-and don't plan to make-any performance modifications on your car, a factory replacement may be just fine. Just remember that such units are designed primarily for sedate street driving. If, on the other hand, you drive like most VETTE readers, a step up from stock is probably in order.
Most companies sell an entry-level performance unit. Fidanza, for example, offers a carbon-Kevlar disc and a high-clamp-load pressure plate. The carbon-Kevlar material is great for a car that's driven on the street daily. Combined with the upgraded pressure plate, this clutch will hold about 20 percent more torque than stock. Even better, its life expectancy is about the same as that of a stock disc.
Kevlar is another common performance-clutch material. The upside of Kevlar is that it's fully streetable but still has enough holding power for an occasionally track-driven car. The downside is that it requires a break-in period, usually 500 miles. Skip it, and service life will suffer tremendously. Most Kevlar units will hold around 45 percent more torque than stock.
If you like to drive your Corvette hard, a ceramic clutch will allow you to do just that. The downside to ceramic is that it has a slightly rougher engagement than stock. On the plus side, it can usually handle around 80 percent more torque than a factory unit.
If you're looking for an "on/off switch" with tremendous holding power, a sintered-iron clutch might be right for you. This material is great for drag racing, but don't even think about using it on the street. Sintered-iron clutches can hold around the same amount of torque as ceramic ones
In recent years, twin-disc clutches have become all the rage. The additional surface area that a twin-disc clutch provides means that even smaller-diameter units can be made to hold incredible amounts of power. Best of all, the latest twin-disc clutches are friendly on the street and relatively easy to install. The only downside is price. For cars that are making more than double the factory torque, a twin is the best and most reliable way to go.
We recently had a chance to sample a twin-disc unit installed in Fidanza's 1,100hp C6 show car. The clutch was able to hold all the horsepower the car's blown LS2 could throw at it while still offering stock-quality driveability. Needless to say, we were impressed.
Now that you have a better idea of how the clutch functions, let's see which clutch combination is best for your car. Start by asking yourself some basic questions.
How much torque is my car making?Most clutches are rated according to torque-that is, the amount of twisting force generated by the engine. This rating is taken at the flywheel-not at the wheels, as with a chassis dynamometer. Fortunately, most chassis dynos can provide a corrected number to determine torque at the crank.
How do I plan to drive my car?Is your car a daily driver that occasionally visits to the track? Or are you a strip or road-course regular looking for the best possible performance, regardless of how it impacts driveability? How you drive your Vette will play a huge role in determining which type of clutch you should choose.
What other modifications have I made that will affect the driveline?Any modification that increases drive-wheel traction-for example, a limited-slip differential or a set of run drag slicks-will put more stress on the clutch, and should be taken into account when making your selection. You may need to use a clutch package that's rated for more torque than your car is actually making.
It's important to keep in mind that every clutch is different, and every clutch manufacturer designs its parts a little differently. That being the case, it's always a good idea to contact one or more manufacturers directly before making a purchase. Ask plenty of questions and use the answers you receive to make an informed decision. Every time you release the clutch pedal, you'll be glad you did.