cmunson

I have a 67 GTO that has a 73 455 (Firebird engine I think) engine bored 30 over. I bought it this way and was thinking of changing the exhaust. The car has hooker headers and what looks like 3 inch pipes going back to the 'x' where it gets skinnied down to 2 inch. The car does not sound like has a big block in it and I think I am being robbed a bit in HP due to restriction.

I was thinking of a 3 inch SS Magnaflow setup and wondering if anyone had done so with a 455? I was talking to one person and they said that you needed some back pressure to keep the engine running right and did not recommend a 3 inch setup. Another friend of mine suggested flowmaster 40's

My goal would be making the engine breath on the output side as much as possible for performance. I want it to sound cool and throaty and demonstrate the big block that it has but not over the top.

I am not a mechanic or expert like many I see posting on this forum and certainly a newbie here. I am guy who loves cars and knows enough about them to talk but not enough to take on stuff like this myself (but starting to learn!). I searched the forum first and did not seem to find what I was looking for. Anyone have any feedback?

 

Rukee

What modifications have been done to the motor beside just a 30 over?? Do you know the compression ratio?

cmunson

Not sure. The guy I got the car from was not the one who restored it. I know it has newer Edelbrock intake and carb, a MSD box and a new cam when the engine was rebuilt but I have no data otehr than this. Does the compression ratio make a difference when choosing an exhaust?

Rukee

I think it should if your pushing like 12:1 or higher you would want a larger exhaust.