I but a new 3in catback on ebay and the piping that bolts to the cat is 2.25 and goes up to about 2.75-3.0 in at the end by the muffler. Is this how must so called 3in catbacks are or is all the piping suppost to be 3in? If im running 15psi with this exhaust and stock downpipe and cat how much horspower will I be missing out on?


heres the url from the auction
http://cm.ebay.com/cm/ck/1065-29392-2357-0?uid=201194103&site=0&ver=EOIBSA080805&lk=URL&Item=8007450758

my thermal research came originally with a 2.5 inch attachment point to a 2.5 inch cat and i had to have the point modified for my 3" cat

may not be the "normal" but its another example of it happening

That's a bullshit cat-back right there. If it's 3 inches then it should be 3 inches all the way through. Don't go cheap especially when you got a turbo if you want 100% effectivity.

My downpipe started at 2.5" at the turbo, but expanded to 3" all the way through the cat and to the muffler. You got jipped.

thermal research is one of the best cat backs out there


i would wager that a lot of cat backs designed for the nt eclipse have a 2 1/2 inch flange for the cat.

i know that apexi does because i just looked it up at road race engineerings website

so i am sure that many other brand names ones do to

umm...I think they're talking about ordering GS-T 3" catbacks ;)

Originally posted by taloniized
That's a bullshit cat-back right there. If it's 3 inches then it should be 3 inches all the way through. Don't go cheap especially when you got a turbo if you want 100% effectivity.

uh I have a $700 Tanabe catback exhaust and its 3" downpipe and has a 2.5" flange.

The reason manufacturer's put 2.5" flanges on the pipe is so it can be used with the stock cats as well.

Originally posted by eclipseman1999
the piping that bolts to the cat is...

Dunno where you live, but if no emmission testing... why not just elimate cat all together and go 3" all the way? Or get a testpipe & replace whenever going in for testing.

Much simpler if able,
- J

Originally posted by J

Originally posted by eclipseman1999 the piping that bolts to the cat is...

Dunno where you live, but if no emmission testing... why not just elimate cat all together and go 3" all the way? Or get a testpipe & replace whenever going in for testing. Much simpler if able, - J

Thats what I did, just went with a 3" test pipe. My downpipe is 2.5, but will soon be 3" as well. Then I will have a 3" turbo back system.

But yah, don't go cheap on the exhaust system like talonized mentioned above. I recommend the Apex'i N1 3" catback for the GS-T's. That is what I use and I love it. Also has a nice deep tone to it.

I've got a 2.5" downpipe (Thanks Matt!), a 2.5" high-flow cat, and a 3" ERT catback (prototype unit). Everything pretty much bolted up without any problems! And having a 2.25" flange is NOT high quality.