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Running mixed diameter intercooler piping?

I'll explain all this in I.D.

I have 2" pipe coming off the turbo into a 2.5" increasing coupler. I have 2.25 and 2.5" pipe. The 2.25 clears my driver headlight better than the 2.5". The inter cooler is 2.5" inlet and outlet. I can clear 2.5" around the passenger headlight just fine. My BOV is welded to a piece of 2.25" pipe that I would like to use. The GM Maf is a 3" with 2.5" reducing couplers on each end. And then runs into the 2.25" intake manifold elbow.

I imagine smaller to larger is okay. Running the 2" from the turbo to the 2.25 into the 2.5" inter cooler outlet. Correct me if I am wrong.

2.5" from the outlet of the inter cooler into the 2.25" piece that the bov is welded to I'm unsure. Will this be a big deal? Of course I'm on a budget and don't want to spend anymore money, IE: have a bov bung installed into a 2.5" piece.

The large change is from 2.5" into the 3" GM maf and then back to the 2.5" pipe (via reducer couplers). Could this also be an issue? Should I look for a 2.5" maf? It ends up in a 2.25" intake manifold elbow anyways???

What do you think?


Well-known member
Apr 25, 2010
Orlando, FL
All those reducers and different sized pipe shouldn't be a problem. More than likely you're not pushing so many CFM's that pressure drop will become an issue.


Well-known member
Nov 18, 2011
Lake Stevens, WA
guys have been running the GM MAF's for ever with reducers. i have never heard of an issue, even with cars making nice power.


Well-known member
May 4, 2003
Clarksville TN
I had a 3 inch out of the intercooler to a reducer to 2.5 which the BOV was welded to and on to the throttle body. Looked like sh*t and drove me nuts because I knew it was wrong. To many fluid classes in school. One Sunday afternoon I took off the coupler and the pipe to the throttle body. I took the pipe and on the inside cut a slit and made a cone out of it by welding in a piece. Was probably 10 inches or so. Car lost 2.5 to 3psi of boost. This was the only change made. Boost is a measure of back pressure so you make your assumptions.

You can buy cone shaped pieces of pipe in all flavors. stainless/aluminum and mild steel or you can make your own. Start with the largest size mark a straight line , then take a straight edge and mark a angle on both sides of the straight line and cut out the wedge. Then take a hand full of worm clamps or better t bolt clamps and make it touch. Stitch weld , cut to the small size and your done. From the centerline over isn't much figure like a 1/4 inch but all depends on the pipe lenght.
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