Most flowmaster mufflers are actually good however the cat back kit they sell for our cars is garbage. Somebody did a comparison a while back, i think on ls1tech, and the flowmaster only flowed a little more than stock. It would be wise to go with something else.

 

WOW a whole two or three horsepower gain...whoopdy friggen do, not like you will feel it! $250 comared to i dunno $450+ for other cat backs...that 200 extra bucks will be going towards my headers where the HP will actualy be felt! and I have $$ left to spare! If you like the flowmaster sound...keep it! use the extra $$ for something that will actually effect SOTP performance!

 

Alot of people think Flowmasters on our cars suck because they are comparing the 80 series with the competition. The 80 series is the quietest muffler available for the 4th gens, and is barely louder than stock at idle and only a little louder throughout the rpm range. The 40 series, the 2 chamber kind, are quite a bit louder and flow better. I believe it was Car Craft or GM High Tech got a 13rwhp gain on a Flowmaster American Thunder catbak on a stock LS1 car.

Jason

 

ummm...yea you have that backwards..the 80 crosflow muffler (muffler used in american thunder catback) is quite a bit louder then the single in/out 40 series catback (called G-force or something)