Quote:
Originally Posted by Eazy-V
Also, I know that air can only move as fast as the narrowest part of the exhaust, so is it safe to say that the 3” portions I have make no difference since my catback is 2.76”?
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That is a common misconception. Exhaust gasses will actually flow faster through a narrower pipe, and have a lower local pressure at the same time. The problem is that smaller diameter pipes have greater losses to friction because of a higher surface area to cross-sectional area ratio.
Another thing to think about is the transition between the 3" and 2.7" sections. If this is abrupt, that's where most of your losses would come from. You are essentially stopping a portion of your exhaust flow, making it turn 90 degrees, pushing it into the rest of your flow, and turning it 90 degrees again before continuing.
So does 3" vs 2.7" make a difference, yes. More so in FI cases because more air means higher rate of loss for a given length. However, most folks in the real world don't see much of a difference from a catback on NA at least. Haven't looked much at FI exhaust comparison myself.