Thread: 06 gxp custom cai

I get it. Now... should I run 4 inch to the maf and 3 in into the tb. My maf is only 3 inches

If I were doing a FWI like yourse, I would use:

Throttlebody > 3" to 4" adapter > 4" bend> 4" to 3" adapter > MAF > 3" to 4" adapter > 4" straight pipe > 4" adapter > 4" bend > 4"-opening filter

Optimally all bends should be 4". A 4" 90* bend has roughly the same properties as 3" straight pipe. Obviously, the ~22.5* bend off the throttlebody and the 45* (is that 45*?) bend at the filter only equal 67.5* total bend, but there's no reason to do anything but 4".

As for the 4" pipe, its all about volume. The larger intake pipe essentially acts as like a surge tank. With 3" its just keeping up, with 4" there is excess air there to keep the flow at max.