DA 50 on both the ones we have here. One has an inverted pitts muffler and is a really nice installation. The flame bird has a canister setup which requires a bit more modification to the fuselage. Not hard and plenty of room for sure but you simply have to build a cavity to shield from the internal fuselage area. The canister/header combo DA offers really allows peak performance from this engine. The Pitts muffler seems to be more restrictive although I think it could be improved be trimming some of the exhaust stacks a little.