I have a 95z with the basic bolt on's. I have a hooker cat back exhuast and with the stock manifolds it sounded real nice. I just put on a set of mac headers and y-pipe. I also took the air pump off but I don't think that has anything to do with it. The power is there but the exhuast is really quiet now compared to what is was before. Its not a big deal but I was just woundering if anybody knows why.

Thanks
Nick

 

My car did the same after I installed some hooker headers. I think its due to the better header design. With the stock manifold on the car there is a build up of pressure and noise when on the throttle.

With manifold my car sounded like it had a turbo. Which was sorta neat since i've got a supercharger.

 

happened to mine as well, the evening out of the exhaust pulses is making the car a bit quieter...but the first time you romp on it you should like it as it sounds much more refined. Even my stock exhaust sounds bad *** at WOT with headers (although its still too quiet)