I have a 91' GTA LB9 700R4. My exhaust is stock (without the cat) to the 02sensor. The it goes to the next size (2 3/4) i guess. It then runs into a Flowmaster 80 series muffler and comes out in duels with about 3 1/2 tips. This is how i got the car. It sounds great but i just got done reading an articale on backpressure and how it isnt good. It was a little to indepth for me to really understand. I just need the basics. If i leave it in first and go up to about 4000rpm and let off it has ALOT!! of poping and crackeling. As im deaclerating it sounds like firecrackers. Im fixing to get a set of headers and when i do should I go ahead and change the pipes all the way back to. The big pipes look tacky in my opinion. I got a set of tips from my friend off thir TTA. Its the chrome duel tips like on the 4th gen Formula. Plus when im going down the highway at about 60mph (2.73 rear) im at about 1700rpm, when i let off i can still hear it popping, Not much but noticeable. All replys will be helpfull. Thanks

p.s The articale mentioned something about it hurts low end torque. Well mine sucks till about 2500rpm.

 

Back pressure is bad, on the other hand too large of an exhaust is bad too. You need to keep the velocity of the exiting gases up to provide a good scavenge of the combustion chambers on the exhaust stroke, if you make the exhaust pipe too large it looses velocity and can't scanvenge properly, the same goes for too small of an exhaust.

 

So what sizes header you suggest? 1 5/8 w/ 2 1/2 exhaust all the way back? Or another combo?

 

1 5/8" headers with a 3" cat back and high flow cat should work nicely, or a 2 1/2"-2 3/4" catback if you have no intention of moving to a 350 during the life of the exhaust system.