Well i'm kind of weary about the gain of 2mph anyways, because i had race gas in and i was increasing timing and boost after each run. It certainly didn't feel any faster. I serouslly doubt that the 5 hp that a new muffler or no muffler at will give me will result in 2 mph more in a trap. It's nice to run 12.8s on pump on a quiet car, you should try it sometime. It's intentional that i have a stock muffler.