What is the big different the too? Such as engine, looks, reliability, and problem that would occur?

 

There really isn't much difference: for the basic 911 Carrera the latter had 3.6 vs 3.4 liters, 320 vs 300 HP and a correspondingly small increase in torque, and weighed about 30 lbs more (no idea why). There was a very slight difference in the front headlight details, and the factory wheels were a different style. I believe the interiors might have been a bit different but not too much. S and 4S models, etc., had correspondingly small details, too, in some cases, nothing big.