It been a while since I have converted a 4 bolt, but I dont remember it being that different in what has to be trimmed off. I definately prefer the bolt on muffler. The muffler that is on my conversion is off the blower. Very small and compact. Weighs 3.5 oz as compared to nearly 6 oz for the trimmer. It is also catalyzed. At a 40:1 ratio I have never seen any smoke. I opend it up with 2) 3/8 holes and it seems to breathe fairly well. Plus I am doing my part to be green . Notice the deflector is facing into the "centrifugal oil slinger" (prop). Hoping it flys/runs well like this as it makes it quieter, if not I will just let it side dump. Noise is increasingly becoming an issue at our club.