The 69 Mach 1 I have has a pretty revved up 408 in it making all of 550-575. Looking at my exhaust and thought it was 2 1/2 however only 2 1/4. In fact I was on my way to pick up some flowmasters but double cked size before getting. Online rule of thumb I’m seeing is 2 1/2 x 2 1/2 for 500 hp

Anybody with direct knowledge? My old z28 has 3” and with just getting the Mach 1 on the road recently with current engine it almost seems like it’s restrictive. Blew a muffler out the other night but could have just been ready to go.

tks
john

Just for comparison. The dodge hell cat when first come out had 2 3/4 exhaust pipes.
2 1/4 will work as 2 1/2 will be better'ish with a x pipe is plenty for 500hp. Keep header primary size around 1 3/4 if you do long tubes.
There are other muffler options unless you like the Flowmaster sound also.

engine masters did a test on a 500 or 600 hp engine. from open headers to full 3" with mufflers and tailpipes and it lost around 12 hp I think. then they ran full 2.5" with mufflers and tailpipes and it lost another 7 or so if I remember correctly. so since no one is running around with open headers the loss from 3" to 2.5" was only the 7 hp so unless you like the sound of the bigger pipes and have room to fit it in then there is no reason to go big for a street car as the small loss is not going to be noticed.

tk you everyone.!! Means a lot. Been out of the loop for some years now.