got in a discussion with a friend and he asked a mechanic. I say that flowmasters actually hurt performance and he said he asked a mechanic and the mechanic said they help. I've read about them being restrictive but how much does this affect an output. I was considering flowmasters, but I'm think more along the lines of straight pipes with huge resonators on the ends

 

you need at least 2 cfm per hp you have, so if you have 300HP you need a muffler that will flow 600 cfm, then it wont be restrictive. Mufflers have different designs, so some work better than others on certian setups, anything will be better than stock and wont get you pulled over for noise vs running straight pipes (which I also wanted to do )

Mufflers help the scavaging effect which helps performance, best thing to do is ask, "What muffler would work best with my setup".

At worst, if you get an absolute crap muffler, you might lose 10hp (more or less) on top end.

 

I looked at a 85 z-28 with duals it had straight pipes running right down by the drive shafts then when it got over the axle it had like 4 inch resonators on it. no mufflers or cats whatsoever. It was actually kinda quiet, just had a rumble to it. I imagine it would be pretty loud if you got on it. but I'd like to do something like that with mine

 

get duals, leave out the cats and get a nice muffler, that is what Im going to do when I can afford to and my car actually drives...prob next month.

 

The Flowmaster Delta Flows actually suck or scavenge the exhaust out. So they would be better than a straight pipe. The best is to have a venturi near the end of the collector. They are so effective that they will actually suck out the incoming air/fuel mixture during overlap.