Originally Posted by RCZ

An underdriven pulley isn't the same as a lightened pulley. UD Pulleys are different sizes than the stock ones and as used to reduce hp-stealing parasitic resistance from the system. The problem with that is that there are some associated issues with under driving accessories like the AC and the alternator and may cause them to not perform the way they are supposed to. Most of the pulley derived power gains aren't from underdriving though...they are from weight savings. Underdriven pulleys seem to perform better than lightened ones because they too tend to be a lot lighter than stock so they have both added benefits.

Originally Posted by RCZ

Its all good ssqpolo - The reason that it may become a problem is because of the clutch engagement. The mass of the stock flywheel allows you to engage the clutch at low RPM's and without much jerkiness. The inertia of the spinning mass (flywheel) counteracts the clutch as it tries to clamp down, therefore allowing for smoother, gradual engagement. If you get rid of that mass, then the flywheel will slow down to match shaft speed much faster (jerkier) and you may sometimes stall if you aren't being careful or giving it enough revs. This is a common issue with the Carrera GT, the drivetrain / flywheel is so light that engaging first gear can be a tricky endeavor. Often people don't give it enough revs...or too many.

By lightening the flywheel AND the pulley, you are making it even worst. Some people would advice that you do one or the other. Usually it is better to go with the flywheel because there's more performance to be gained there...However, on some cars, it is OK to do both...Hence my question