exhaust MM question

[mjjstang]

Alrigh I was on Phase2 lookin at a rsr exmag system, and they say that 75mm is 3 inch, Well I see other places saying that 80mm is 3 inch, It seems most all things like down pipes testpipes and the like are mostly 3 inches, now why would they make 80mm exhausts that are over 3 inches, so im pretty much thinking that 80mm=3 inch, can someone confirm this for me. thanks.

[sykikchimp]

onlineconversion.com

[AAA240SX]

75mm. is 2.95 some odd inches. Standard size for stock turbos or superchargers.
80mm. is 3.15 inches. Slightly oversized diameter gives better exhaust flow for
overboosted turbos.

[mjjstang]

but all 3 inch downpipes and cats will bolt up to 80mm right, I know this is stupid but i just want to make sure. thanks.

[AAA240SX]

What brands are the downpipe and cats ur using? Most 3in. pipings use the same bolt pattern to be interchangable (EX: Blitz uses 3-Bolt, Stock uses 3-Bolt).

Yet, some brands may be different. Give me the brands of the products you are using and I'll check them out for you. I have a ton of prods. here in my shop. Let me know...

[mjjstang]

well I am lookin at a n1 catback, (yes I know I have no originality, but I dont want something loud) and dont know the pipe yet, but I do have a Q about the cat/testpipes, some I see have the three bolt and then others have the two like on the factory setup. well ill probably buy the catback, then a downpipe and then go from there to make sure I got everything right, Also a side question, Ive seen on ebay that they sell the cats, but they are very sneaky about it, some say cat but it looks like a test pipe. dont all true cats, even high flow cats, have the same shape, like all OEM cats, Some have the bulge but it is still round unlike the ovaly true cats.
Basically I want a cat that will make it legal, but the best flowing one.