Early and Late 964's

[Dbelleperc]

What is the difference between the 89.5-91 964's and the 92-94 964's except the areo mirriors. And is there any performance difference.

[eion]

There's no real performance difference at all. Other than the Aero mirrors, there were a few very minor changes from year to year:
- throttle valve assembly modified in 1990
- pistons modified in 1990 (groove between top and second ring down was added)
- cylinder and cylinder head gasket modified in 1991 (to prevent the infamous leaking problem)
- cylinder base O-ring changed from silicon (black) to Viton (green) in 1991
- driven gear on intermediate shaft changed from steel to cast iron in 1991
- aluminum intake manifold changed to fiberglass and plastic in 1991
- idle-speed stabilizer modified in 1991
- factory fill changed from mineral to synthetic oil in 1992
- Freudenberg dual-mass flywheel replaced in 1992 by a LUK unit
- distributor vent kit added in the factory from 1993 (but all 964s should have had this retrofitted)

Having said there are no significant performance differences between the years, there are performance differences among the 964s. From 'worst' to 'best':
- Carrera 4
- Carrera 2
(a contentious one, I know, but all the stuff I can find says that a C2 has better performance - it's much lighter, after all. Obviously it's a different matter in the rain or snow - and hey, I'm biased )
- RS America
(not really a proper RS IMO, just a touch lighter than a normal C2 - also around $10k cheaper originally)
- Euro RS
(definitely a proper RS)
- Cup
(really rather special)
- 3.3 Turbo
(the 964 Turbo from 1991 to 1993)
- 3.6 Turbo
(the 1994 Turbo, a very special beast indeed)

Hope this helps!

edit: extra detail added

[Dbelleperc]

Thanks a lot Eion for the info.