uhm... if you cut the 2.5" pipe running into the canister off and make the inlet to a 4" the inside baffles are still going to be 2.5" and if you remove those then that will not be a muffler anymore... and the race pipe would be more quiet than that.... you could always run the exhaust through two race mufflers... but unless you have alot of displacement and/or are boosted with a huge ass turbo... the 4 inch muffler is really unnecessary....