I was thinking about puttin new headers a new y-pipe and a high flow cat. How much horsepower will that add, also that should make the car much louder, right?

 

I recently put on a magnaflow highflow cat. Huge improvement as far as the sound goes to the 305. I already had a flowmaster 80 series on the car before hand which barely did anything with the stock cat, but the new highflow deff brings out the flowmaster, as far as power goes really didn't notice a change, you'd see that more with new headers which I'm still working on replacing on mine. So if you want to improve the sound I highly recommend a new cat.

 

Ive been told, yet to know for sure but ill let ya know next week if i play my cards right, that if you do new headers, cat, and a 3" exhaust, youll make an easy 20+ horse. Not bad.

 

Keep in mind that wnen you free up the exhaust, the extra 20 horses come in at high RPM, where the old system was choking up the engine, so you may not notice much of a difference from a dead start.