Understanding High Performance Clutch Options For Your Next Project Vehicle
What separates a high performance clutch from a standard clutch? In a world where power is increasingly cheap and easy to squeeze out of both large-displacement V8s and small, but mighty, turbo fours, a clutch is often the weak link when looking at a factory drivetrain. Knowing what kind of clutch upgrade to make can often be the difference between a successful quarter mile pass, or trail run, and having to call a tow truck to get back home.
What's Inside A Clutch?
There are three major parts to any clutch. The flywheel is attached to the engine's crankshaft, and the pressure plate is bolted to the flywheel. In between is the clutch disc, which is attached to the input shaft of the transmission.
Since both the flywheel and the pressure plate rotate with the engine, the clutch disc is the key to transmitting the rotational force of the motor to the transmission, and therefore on down the line to the driveshaft. The clutch disc is pushed by the pressure plate onto the flywheel by either coil springs or a diaphragm spring, which are released by the throw-out (or 'release') bearing when you push your clutch pedal, disconnecting the engine from the transmission so you can shift gears.
Materials Matter
With a normal vehicle, the clutch doesn't have to deal with massive amounts of heat or torque transfer, but a powerful 4x4, sports car, or dragster can amplify those stresses considerably, especially when driven aggressively. There are several ways a high performance clutch is designed to better handle tough operating conditions.
The first is substituting different materials for the friction surface of the clutch disc. As with brake pads, the kinds of materials that provide smooth, and quiet operation over a long period of time don't necessarily stand up well in a performance environment. For this reason, most aftermarket clutch options swap out standard organic materials (woven fiberglass, resins embedded with metal oxides, etc) for those that can stand up not just to engine torque, but also the clamping force exerted on the disc by the pressure plate, and the heat that is generated by the friction associated with clamping and unclamping.
Kevlar is a long-lasting option that keeps clutch operation smooth, but doesn't resist heat as well as a heavy-duty organic clutch face with additional metals added to the mix. Clutch discs with a ceramic surfaces are renowned for their ability to resist heat, but a price is paid in terms of smoothness when engaging or disengaging the clutch, while cerametallic materials made from steel, graphite, silicon dioxide, and other metals, take heat resistance to the next level and are even more difficult to drive in a non-race scenario. In between are many copper, carbon, and other material combinations each with their own particular power ratings and driving characteristics.
Shaping Up Clutch Plate Design
Plate design can play a major role in the longevity and capability of a clutch. A multi-plate clutch stacks clutch discs stacked on top of each other, boosting the amount of torque that can be held without requiring as aggressive of a material to be used, which improves drivability.
In addition, paddle or puck clutches that separate out or 'notch' parts of the disc surface pushed up against the flywheel provide more aggressive engagement (through the additional pressure placed on them) at the expensive of increased chatter. The more 'pucks,' the greater the pressure being transferred, and the more abrupt the connection when you let up off of the pedal.
There's also the design of the pressure plate to consider. It's possible to significantly increase the amount of clamping force provided by a pressure plate through the use of stronger springs (or spring, in the case of a diaphragm design).
Balance Is Key
Knowing which type of high performance clutch will work best for your application comes down to understand the amount of power you are working with, the trade-offs you are willing to make in terms of street driving, and the type of racing or off-roading your are doing.
In all but the most extreme applications, working with a clutch disc material and design that preserves smoothness of shifting will make for an experience behind the wheel that won't have you hating your ride when you're not driving flat-out. Balancing heat management, strength, longevity, and comfort are key to enjoying your project and not cursing your clutch.
