The fourstrokes that I mentioned usually come with a muffler. If it is not included then I would buy the stock muffler for them because it is small and quiet. I would try to raise the fuel tank 1/2" or so because it usually is to low for a uprighted fourstrokes in most planes. It might works just great without the modification but incase there is a leaning situation " usually at the lower rmp range" then you you what to look for.