Hey Bounty, the larger muffler is much more effective on the newer OHV engines, i have tried using the auto mufflers on the older flat head Briggs & Stratton engines and it does does take some of the bass note out of the engine noise but it is still loud a 100 feet away. I currently have one of the flat head engines on the spare generator that i loaned to my neighbor during all three of the hurricanes that blew through the neighborhood last year, they had it on the other side of thier house and we are on acre lots. They get up around 6 am because at 6:05 the gen set started up and i could hear it quite well. I have since reinstalled the factory muffler (much smaller package without the big can) and i can't tell any difference in the sound when it is over there. And i am not complaining about the noise, but if i lived in a neighborhood where the houses are close together it might be a different story. And having a spare gen set has it's benefits, while i re-wired his well pump to run on the generator he went out gas shopping. I definitely had the better end of the deal.