Stock VW Beetles are quite reliable in their stock form when they are driven accordingly. However, when the horsepower is increased, and/or the vehicle is subjected to abusive starts and/or power shifting, breakage often occurs. Parts subjected to the highest shock loads which are most prone to breakage are: axles, CV joints, ring and pinions, first gears, and flywheels coming loose, even when all of the proper strength components and building techniques are utilized.
The primary reason that these parts break, is not always just more horsepower, but excessive shock. Whenever the clutch is engaged fast or slammed shut, this shock travels through all of the drive components. The most common situation in which this occurs, is starting out fast in first gear (such as a drag race start). The engine speed is increased to a high RPM and the clutch is engaged as rapidly as possible. When the clutch slams closed and locks up, a large torque peak (shock load) is created which greatly increases stress on all parts. This drag racing type of driving is lots of fun, but it sure is hard on the drive train.
These shock loads are transmitted through the clutch, then 1st gear, spider gears, ring and pinion, CV joints or axles to the tire and will also be transmitted back through the flywheel and crankshaft when full lock up occurs. For street driving with rubber mounts, the parts will withstand some of this type of abuse. However, it will eventually find the weakest link in the chain and that one will fail if you continue to treat it this way.
Generally speaking, when any clutch stronger than stock is used, the shock load to the drive train is increased. One reason for this is because stronger clutches will normally have a narrower working range and engage faster and harder.
The clutch spring diaphragm is also much stronger and will slam closed with much greater speed. Likewise, when a disc that is designed to lock up without slippage is used in a race application, even with a stock pressure plate, the shock is increased in the system. Of course, stronger clutches are required for modified engines that put out more horsepower and torque than a standard stock engine. Which one to use is something your parts suppliers should have a great deal of experience with in order to assist you with the proper choice.
Many people have attempted to reduce breakage by installing a Cush Lok fabric disc that slips each time it is engaged. Unfortunately, there is no way to ever control this slippage. It changes from run to run and the pressure plate and flywheel distort badly from this slipping. Some would slip too much and not even last for one run and another might last for one race. It is impossible to be consistent with the car, and consistency is required to win races. In fact, any combination that cannot be reliably engaged time after time should not be considered for any application where dependability is important.
Don't despair, there is a way to use stronger clutches that engage properly without slipping and will also reduce parts breakage for drag racing. The general idea is to control the speed of closure of a strong enough pressure plate and/or 3 puck disc, to close at the exact rate to have it hook up properly. However, you do not want it to slam closed so fast and hard that it causes breakage. In other words, a clutch engagement shock reducer.
The "Washington Anti Shocker" (™) is an adjustable hydraulic shock absorber. It is about the size of a small cigar, and it mounts on the driver's side of the car, right on the transmission. It is held in place with the upper engine attaching bolt. It contacts the clutch arm. It must have the pressure plate properly adjusted, as in our pressure plate instructions. So the arm is back in its proper operating location and any forging flash must be removed so you have a flat, square surface for the Anti Shocker to contact. The clutch engagement shock reducer is adjustable from zero to maximum shock reduction affect. A numbered dial is on the device, which enables precise adjustment. It is locked in place with a set screw.