[stigler4profit]

If you size an exhaust correctly, meaning not too big.. you can potentially gain MPG. Because the engine, being a pump, will not have to pump as hard to expel gases as it would with a smaller diameter pipe. I personally saw gains of 1-2mpg with going from factory 2" to a 2.5" dumped exhaust with a turbo (free-er flowing) muffler than with the factory exhaust on my (now gone) Explorer Sport. In addition I ran straight exhaust on my Mustang GT, and saw 1-2mpg better by doing so.. without going larger in diameter. On my wifes little MX-3 it gets the same mileage with the 2.5" catback into a quiet universal muffler as it did with the factory sized pipe installed, yet it does accelerate much better.