just wondering if anyones noticed a significant hp gain in there stock 305 tpi with just adding headers and a cat back system? I have a full stainless SLP tol cat back and coated air tube headers.

 

Headers and 3in exhaust will wake up any engine in a 3rd gen because the stock exhaust is strangling the engine. I had an Lg4 once I put headers on it and it went from barely spinning tires on a launch to lighting them up. Headers cut a half second in the 1/4 on a 350 build I had in an 87 GTA.

 

My headers haven't woken up my old 305 but, they wake up my neighbors!!

 

 

I'm with the above post- I installed hooker shorties and 3in all the way back, removed the cat and noticed a much better preforming engine. I installed a cutout in place of the cat and other than for the sound, I'd skip that if I did it again...you notice a good drop in torque with it open. But it screams when its open.

 

My stock 305 ran 15.0 in the quarter mile, after 1 5/8 shortie headers and full borla cat back it ran 14.40. Def felt the difference.

 

Headers will help a little. Usually about 7-10 hp only but they will make it sound much throatier.

 

Not sure where you came up with the 7-10 HP number. Its more like 15-20 HP with decent headers on a decent exhaust system. I have seen even mild 305s and 350s pickup over 40 ft/lbs of torque in parts of the torque curve as well.