What about 996 or 997 water cooled motors?
They are inexpensive, make very good power, and are about the same size and weight.
A few issues:
- They ae water cooled. That means they need a lot of plumbing.
- They cannot be used with any pre-1999 transmission – the bellhousing is completely different.
- 996/996 transmissions will not fit in the standarf pre-1990 chassis because they are too long
- Fitting 996/997 transmission one requires removing the torsion tube, which means figuring out what to attach the rear suspension to.
- Bellhousing adapters are difficult to impossible to use, because the 996/997 engine and transmission relies on a starter mounted to the top of the engine. This is not possible with the 915 or G50
- Electronics are complicated. Afermarket woudl be needed.
- 996/997 engines are generally unreliable due to intermediate shaft bearing issues.
Bottom line: Don’t bother.
If you really want a water cooled engine go for a GT3 or 996tt. These Metzger engines are compatible with 915/G50 transmissions. There is still the issue of plumbing the coolant, but these engines are powerful, reliable, and…well…expensive.