i am going to get a comptech header for my 98 ls and dont know wether to go with a 2.5 or 3 inch. It will be attached to a high flow cat and that will be attached to a 2.25 rsr exhaust. Im thinking that going from a 3 inch header to a 2.25 exhaust might be too much of a difference in the cat and will create too much a bottle neck effect. Im not to sure which would be better. Most people say the bigger the better but if my exhaust is only 2.25 it might be too restrictive for a 3 inch header please write back.

 

RSR is relatively free flowing in comparison to the oem exhaust.

Wouldn't make a huge difference either way, but you have to ask yourself, are you ever going to increase the diameter of the catback? Ever going to supercharge it? You have to look at the future roadmap.

-Junior-

 

you dont need a 3inch collector, Bigger is not better. Big is good when you have enough power to used it. But big and no power will result in losing power... If you want 2.5 inch, you should get a cat back system that is also 2.5 inch. No point of getting a 2.5 inch header and then step down to 2.25 cat back.