so i am getting a Greddy EVO2 cat-back exhaust and spyder 4-2-1 ceramic headers installed on my car tomorrow. I know the only way to figure out the exact horsepower is to get a dyno test done, but how else can i get an estimate on how much horsepower gain i will have?
Thanks

 

Easy: about none. Nothing you could feel at least, but enjoy the sound!

 

sorry but i want to disagree. The purpose of an after-market exhaust system is to increase power and torque. i know for a fact that most of the horsepower is generated in the headers. the bigger the air flow the more power there is...

 

And it will, but you will barely notice it. The power increase will likely be around 10hp at the wheels, you'll lose your low end torque, gain some high end, and it'll probably sound great.

I'm not saying you won't gain anything, I'm saying you won't gain much.

Search around here... there are a ton of threads discussing exhausts, headers, and backpressure and such.

 

No. ALL of the power is generated by the air flow. The only way to increase power is to increase the flow of air & exhaust. Headers (or intake) can only improve things only to the extent that some other component becomes the dominating resistance.