Hi-Po Clutch Revolution
RLR's new Rev-6 (inch) high performance VW clutch
Any time the subject of high performance clutches comes up, you usually hear about either high pressure assemblies from Kennedy Engineering or adjustable clutches from a J&G-style assembly. By far, Kennedy has the lion's share of the high performance street and drag racing market, with their various stage 1-4 pressure plates, and different aggressive single discs. With full-on drag applications, racers tend to move to adjustable clutches by changing the stack height using a handful of thin washers under each mounting stand. For the most part, a performance clutch needs to be able to hold the power that is applied and control slippage. But at the same time, it also needs to allow the driver to make shifts by quickly disengaging the transaxle from the engine, and then just as quickly engaging back up. All this has to happen in a matter of moments — tenths of a second, as any delay will slow the whole process down. It then becomes a balance between these two issues — shiftability and engagement — that most racers face. For just about all performance air-cooled VW applications the stock 200mm, or 7.87-inch, clutch is the standard size, and has been for years. But in recent times, many "non-VW" racing applications have moved to a smaller, more compact diameter clutch. One of the reasons that a smaller diameter is desired has to do with inertia.
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. And as the weight from the outside of the clutch is reduced (by using a smaller diameter assembly), the rate of inertia is also reduced, which makes changing the transaxle input shaft rpm easier. This fact directly effects how well you can make quick shifts at high rpm and torque. In order to make a shift under power, the transaxle input shaft needs to change rpm, which can only happen once the clutch is depressed. For example, if you accelerate to let's say 8,000 engine rpm at the top of first gear, depending on the gear ratios, the rpm drop to the bottom of second gear could easily be 3,000 rpm or more. In order to match the vehicle's speed at that point, that is to say, the input shaft has to slow down to 5,000 rpm in order to allow the transaxle to make a gear change. A well balanced clutch will allow this to happen quickly and efficiently, and then lock up and hold the power at the top of each gear.
With these ideas in mind, Ron Lummus of RLR has come up with a new adjustable clutch that he feels offers the best of both worlds. Called the Rev-6, Lummus has taken a queue from many of today's modern clutch builders and has created a new clutch for the VW market. It measures only 6 inches in diameter, is adjustable, and comes in either a single- or dual-disc assembly.
One of the first points that comes up when discussing using a smaller clutch is the flywheel itself. Knowing that a stock 200mm flywheel's disc surface is no smaller than 5-inches at the step, a smaller disc will only come in contact with a portion of this mating surface. To address this point, RLR not only offers a number of new flywheel setups specifically for this application, but has also created a steel adapter plate that attaches to the stock flywheel and widens this disc surface area. This adapter fits directly on top of the flywheel surface, and is attached using a series of twelve 10/32 screws, countersunk into the plate itself and then surfaced. This plate registers on the flywheel inside step, and you drill directly through the plate into the flywheel. Around the adapter perimeter, there are six 3/8-inch studs installed, which locate the drive stands, floater (if used), pressure ring and clutch cover. The original 8mm clutch holes are no longer used for this application. For applications that use flanged crankshafts (Pauter, Scat or Bugpack), or a Type 4 crank pattern, RLR makes all-new flywheels that are ready to use this new clutch.
The Rev-6 clutch is adjustable like the J&G, using a series of six studs with shims placed on top of the stands to set the stack height. Shims are .020-inch thick and are placed between the stands and the clutch cover. Adding or removing shims for these stacks will adjust the pressure plate finger height, which sets the point of engagement and rate of release. The idea is to allow a certain amount of (controlled) slippage on the starting line and perhaps into second gear, to soften the launch somewhat, and allow the tires to keep up with the available traction.
There are also three rocker arms fitted to this pressure plate which increases the load applied to the disc by a 5.0:1 ratio. As the engine rpm (and inertia) rises, these arms rotate into position, thanks to centrifugal force, and push down to lock-up the clutch disc. The clutch's ability to hold is then increased by 20-30% — better overall than most 200mm clutches. For most applications with between 200-350hp, RLR suggests using a single disc setup. But once you get above 350hp, in turbocharged applications, then a dual setup is highly recommended. In this case, two 6-inch discs are used along with a 3/8-inch steel floater plate. Discs come in two different friction coefficients but each are made of a Sintered iron material, and measures .250-inch thick. The center hubs are new and are heavy-duty to withstand the increased loads, and the clutch diaphragm is also available in two different thickness.
One of the byproducts of this new clutch is the reduced pedal movement required to engage and release the assembly. In most VW cable applications, you need to push the pedal about 6 inches from top to bottom (which, when you add all the deflections normally associated with the stock pedals, cable, tube and cross shaft, is more than most other automotive applications). Using the RLR clutch, if you have the rest of your clutch linkage properly set up, you can reduce that number down to only 3-1/2 inches. This translates to quicker clutch engagement by your foot, which needs to match that of your shifter. Overall, the RLR clutch should make speed shifts quicker and cleaner than ever before.
The beauty of the RLR clutch is that it will fit into any 200mm transaxle housing without issue. Even when you are using a dual disc setup, it will not interfere with the cross shaft and throw-out bearing arms. For more information about the RLR Rev-6 clutch, contact Ron Lummus and he can suggest which setup will work for your application.
Ron Lummus Racing
2910 E. Miraloma Ave., Unit B
Anaheim, CA 92806
Ron Lummus Racing
2910 E. Miraloma Ave., Unit B
Anaheim, CA 92806