I got new exhaust today. The Thunderbolt cat-back system. The thunderbolt is identical to a flowmaster 40, so for all pratical purposes its a 40 series. It sounds awsome. However, I was told my gas mileage would slightly increase and it seems to have dramatically decreased. Will this get better soon, or whats the deal?

Also would just dropping in a K&N air filter help with mileage?

 

exhaust should not decrease mpg. One reason that would happen is if you have been riding it fairly hard to hear that new sound, or the pipes you have run are too large (poor exhaust flow). Never heard of thunderbolt maybe that is it?