Is there a formula to figure out what size mufflers to use. I have two small glass packs on my 337 flathead. I think the exhaust might be a bit restricted. I would also like to quiet it down a bit. I am using the stock iron exhaust manifolds. The current exhaust has just one 90 degree bend and then about 8 feet of strait pipe. The glass packs are in the middle of the 8 foot run. I would like to replace the the strait pipe and glass pack with stainless.

John
NNY

 

"Regular" 239 flatheads seem to sound and run best for the street with 1-3/4" dual exhausts. Are your glasspaks straight-thru, short ones? I doubt they are a problem.

 

Agree, the only glass packs I've ever seen were straight thru. Don't see how you could have any exhaust restriction with those...