Originally Posted by Russ13
Does installing an aftermarket exhaust on a 4.0 really improve MPG and HP???
I'm sure that it will do better than the stock exhaust that's for sure. Most of the aftermarket exhaust use piping a 1/2 inch to an inch bigger than stock, that will allow more emissions to exit the vehicle quicker, then allowing more power to you, so I would say more HP and less MPG if you have a heavy foot, and more MPG if you take it nice and easy.