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In our experience, we have found that once an engine's horsepower output exceeds 130hp, the installation of the engine and gearbox requires careful consideration.
If the engine is not installed with extra mounting hardware and uprated rubber components, movement of the engine and gearbox will occur resulting in, at the least, broken stock rubber mountings, or at worst, a broken gearbox.
We have seen many instances of broken gearboxes that have been attributed to incorrect engine and gearbox mounting. When the vehicle is launched hard, the frame forks (unless supported correctly) will flex - the end result is a phenomenon commonly known as 'wheel hop', or 'axle tramp'.
When a vehicle wheel hops, the tyre momentarily looses grip on the road/track surface as the frame forks flex. As the frame forks unload, the tyre grips again causing the frame forks to flex. This repetitive flexing and unloading (with the resultant tyre intermittently gripping the road/tack) loads and unloads the gearbox many times. This movement is like putting 140hp air hammer through your transmission. This will do severe damage to the ring and pinion and other gearbox components.
Sometimes, wheel hop is barely detectable inside the car. By the time you can feel it, it is already damaging your gearbox.
As long as the engine and gearbox are correctly fitted to the car using the methods listed below, and when launching your car you obey the cardinal rule of pre-loading your gearbox on the handbrake/line lock, your gearbox can be made to live as long as possible.
We fit new genuine VW 'grey' heavy duty rubber mounts.
We supply and fit an intermediate mount which bolts to the gearbox intermediate housing and has brackets that require welding to the frame forks of the vehicle. Rubber mounts fit between the frame fork brackets and the intermediate mount.
We can also supply solid aluminium blocks to replace the rubber mounting blocks. These can be fitted permanently or swapped for the rubber items if a weekend's racing is planned.
We only use Gene Berg traction bars as they are of solid enough construction to do the job correctly.
A CSP trapeze bar can be fitted. This is especially useful on vehicles such as the Karmann Ghia. It is difficult to use a traction bar on a Ghia due to the inherant lack of strength of the rear bumper mounting area where the traction bar would mount because of the increased rear overhang of the Ghia body.
However, we have found that on a customer's Ghia fitted with a 2110cc engine mounted with grey VW rubber mounts, intermediate mount and CSP trapeze bar, slight wheel hop still occurred when an incorrect launching technique was used.
Once the engine's power output approaches the 180 to 200 horsepower mark, rubber mountings become inadequate for the task required of them if seriously hard usage is planned (e.g. drag racing). Solid mounting of the gearbox with additional bracing into the body shell is the only way to guarantee zero movement.
The downside of solid mounting is the greatly increased amount of vibration transmitted into the vehicle along as well as increased noise levels. Ancillaries mounted on the engine (e.g. carburettors) require additional securing (e.g. spring washers, thread locker and nyloc nuts) in an attempt to stop items from vibrating loose.
A rigorous maintenance routine including checking the tightness of all fastenings is required. Usually the type of vehicle that has solid mounting sees limited use, so this shouldn't be that much of a problem.
We supply a Bugpack solid mounting rear gearbox mount then make additional brace bars fabricated from CDS tube. These bolt onto the Bugpack mount and onto additional bracing fitted on the rear luggage bay area. If the vehicle has a roll cage, bars can be added to tie in the roll cage to the bracing on the luggage bay area.
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