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:

  1. They ae water cooled.  That means they need a lot of plumbing.
  2. They cannot be used with any pre-1999 transmission – the bellhousing is completely different.
    1. 996/996 transmissions will not fit in the standarf pre-1990 chassis because they are too long
    2. Fitting 996/997 transmission one requires removing the torsion tube, which means figuring out what to attach the rear suspension to.
    3. 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
  3. Electronics are complicated.  Afermarket woudl be needed.
  4. 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.