I`ve posted this a few times before.
I used 3 1/2' x 12" long (ROUNDY ROUND) bullet mufflers, and welded 3 1/2" spiral cores in them about 1/2 way in. Full 3 1/2 " (collectors are 3 1/2'') exhaust turned straight down in front of the rear end. No drone , no popping , not extremely loud, and none to little back pressure. All this was bought for under $50 at the time, minus the 3 1/2" exhaust pipe. U will not need 3 1/2" w/ smaller engines tho .
If u shop around, these can still be had pretty cheap.---jfyi
