Okay so I just purchased my 85 firebird with a 305 HO a few days ago, and am planning on getting the exhaust done right away. I am either going to

a) Take the catalytic converter off and go straight pipe

b) Take the catalytic converter off and go with a Flow Pro muffler.

Could anyone give me the estimations on the gains I would get horsepower wise?

 

not that much. and its illegal either way buddy. i guess if i had a choice id put the fake converter there so at least visually you'll look okay..now unless they check the #'s on it...

 

Well actually, I am from Canada, and it isn't illegal here, the worst I can get is a $90 noise ticket. Also I am mostly curious about which one will give me the biggest increase. I know it wont be much but I would still like to know.

 

straight pipe will give the most "increase", but its still negligible at best. Unless the cat is clogged. Perhaps pickup a aftermarket hi flow cat? it will keep the car from smelling bad, and wont cost much if any power. you most likely wont feel any difference in performance between a straight pipe there, and a high flow car.

the most increase you will notice from the exhaust would be to swap out the stock exhaust manifolds and y-pipe to aftermarket headers and y-pipe. You will most likely feel this change.

 

I am talking about taking BOTH the cats off and the muffler.

 

my friends z28 was like that it was pretty loud and popped like crazy you need to have some back pressure or you could accualy lose power.

 

I was thinking that but wasn't sure, so basically the Flow Pro would be the better option then.

 

I would defiently have some sort of muffler.

 

straight shot classic cherry bomb put where the cat goes, then straight pipe out the back, no axle loop.