3" exhaust reducing down to 2 1/2" after x-pipe

When the exhaust leaves the manifolds (or headers), it's super hot gases, as it travels towards the rear it cools....this is a known fact. Any gas contracts as it cools, another fact. So as the exhaust gas travels towards the rear it needs less space because the same volume of gas gets smaller. Theoretically...your pipes could get smaller towards the rear and still be able to carry the same amount of exhaust. Of course smaller pipes (towards the rear) will also increase pressure (with the same volume). So if you use larger pipes as the exhaust goes towards the back of the car it will give the gases more room and decrease the pressure which should allow more flow!!


Theoretically speaking!!
treblig