My 92 z28 305 TPI seems like its running weak... the engine sounds and seems to run very strong but I am almost certain that the catalytic converter is clogged... How much would a clogged converter reduce performance? Also, would an exhaust shop remove the cat. and just put a pipe in place? My car is mostly in GA and over there they have no emissions regulations or anything... so would they not do it for me in NY?

Also, I am pretty sure that I have a 3" exhaust system all the way from the headers straight to the back if its not 3.5" Do you think this is way too big for a '92 305 TPI? The car definetly seems to be kinda slow from a dead stop and I am thinking it is a combination of the large piping and clogged converter.

 

Could be the cat, but try getting yourself some bigger tires as well. Like 235 60 15 and you'll notice the difference. If you make any decent power that bigger tires are a must. However, it wouldnt hurt to get the converter in.

 

Is your exhaust stock, and do you have dual cats? If it is stock, you probably have 2.5 inch pipe from exhaust manifolds to cats. If you have the performance enhancement package you would then have a 3 inch intermediate pipe. The reason I know these things is that I have a 1992 Formula, 305 TPI, 5 speed, dual converter exhaust with the performance enhancement package. I think that mine has a pretty good amoiunt of power down low, but runs out of breath around 4500 rpm. (Course it is all stock except for a flowmaster series 80 muffler and a K&N airfilter) Hopefully I can do some things to get a bit more power, maybe next year after the paint job.
As far as tires, are they 245/50/VR16 and do you have 4 wheel disc brakes? If so, forget aboout going to a set of 235/60/15 tires. The rims for the 15 inch tires won't fit over the disc brake housing. Tried it on my car when it was going into storage, and I ended up taking them right back off.