I just got my friends flowmaster off his LS1, it has everything you would get in a LS1 kit (http://www.ls1f-body.racenet.net/exhaust.php scroll down a little bit) The only thing im worried about is the pipe that goes over the axle may be different than the one connected to the flowmaster, looks slightly different.

Im going to take it tomorrow to see how much it would be for install but im not sure if it will fit. I was thinking of maybe just cutting off the inlet pipe on the muffler and cutting off the stock muffler from the inlet pipe aswell, so i dont have to mess with the i-pipe, ya know? If i did that i could just do it myself.

which should i do

 

i have a flowmaster kit from an ls1 on my 96, but it didn't come with the i pipe. I just had the i pipe that was on there welded to the flowmaster....i think my car might have had a cat back on it though, so the i pipe might have been bigger than stock? from muffler back though it will fit...sounds pretty good too.

 

Well my LS1 flowmaster has the catback but no i-pipe. I just measured the inside of the cat back and it is 2.75 which is the same as my i-pipe, so im not sure how the muffler shop would weld that on.

Also, is the cat-back important to hp gain? compared to stock?

 

up to the front page, hope to get another reply

 

you said that the two pipes are the same size right. if they are then the muffler shop will just expand the i pipe to fit over the muffler. simple as that. oh yes it's important, yuor engine needs to breath freely and a catback will help the next mod i would add headers, big gains. good luck