I'm redoing my entire exhaust. I have already purchased a set of hooker long tubes and a dynomax I pipe. My plans are to have two electric cutouts right after the headers, and a full system into wye pipe then back to a muffler in the stock location. This car is mainly my daily driver with some track use. Because of this, I want it quiet during normal operation. Dynomax has a stock replacement style muffler to imitate the sound of the OEM muffler. The problem is, the inlet is 2.5". The system will be 2.5" off each header (to keep some ground clearance) into the cut outs. It will remain 2.5" diameter until it combines into a 3" wye pipe. It will be 3" back until the muffler.

My main question is, will the muffler be enough of a restriction to make an impact in daily driving or gas mileage? Currently the engine is a mostly stock 350, but plans include new heads, intake and camshaft putting it into the 400hp range at the crank. How will daily use and gas mileage be affected at that rating?

 

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