On several planes I had problems with the pass-through screw the muffler on a Evolution 46 NT. I found the screws were stretching, primarily when the engine was run hard or high rpms such as on a quickie 500. Two bullet proof solutions are the Macs black muffler for lighter than stock with stock like performance or a Jett tuned muffler for a power boost. It looks like Evolution has contracted with Jett to supply (blue) tuned mufflers to their product line as well. http://evolutionengines.com/Products...x?ProdID=EVOM1