I drove my 944S about 7k without knowing the balance shaft belt was toast - I thought the motor itself was just rough and that the timing was incorrect.
Once revved, the motor was ok (like on the highway). I'm telling you though, the car will vibrate itself apart in terms of motor mounts, cat converter and muffler (which were quick to become toast). Also, all of the heat shielding started to rattle. It will be much worse than a 924 because the pistons are much bigger. The inherent unbalance in a 4 cylinder only gets worse as you increase the displacement. This is not true with a motor such as the boxer six in the 911. My advice if you are going to drive the car daily is not even to consider leaving the balance shafts out. Trust me on this one!
Erick
------------------
Erick
86 951
http://www.pelicanparts.com/cgi-bin/pmpre/pm.cgi?action=display&login=aka_951