Turbo-Back exhaust

[Gabriel Shim]

I ordered a 2.5' downpipe but was informed that I maybe receiving a 3' downpipe. My situation is that I had my O2 housing ported to 2.5" and I have already arranged with the muffler shop for a 2.5" from the downpipe to the muffler.

My question is, will having the 3" downpipe and having the rest at 2.5" HURT the st up, or should I return the 3" and remain with an entire 2.5" exhaust system?

I have to get back with an answer as soon as possible, so any input is greatly appreciated.

Thanx

[Marty van den Bosch]

3" would benefit, not hurt. The benefit will not be overly great since the rest is 2.5, but it will be better not worse at any rate.

The issue will be in mating the 3" to the cat, but it can be done by the muffler shop.

[Kimyee Lai]

You really don't want big diameter changes like that.  It disrupts the flow of the exhaust gases.  Now, in your case though, chances are somewhere down the road you'll probably be upgrading your catback to 3" anyway, so I say keep the 3" downpipe.

[Gabriel Shim]

I'm worried about boost creep.  How much of a boost creep would I experience in a 3" downpipe to a 2.5" cat-back set-up?