I don't know if they have head gaskets (I've never had the head off mine) but w8ye is right about using a bigger prop.

You can use the recommended 11x10 to run them in (because you're not going to run at full throttle for extended periods) but I find a 14x6 is great for sport flying and a 13x8 is just about right for warbirds (pulling 10,400 RPMs on the ground when peaked but richened out to 9,950 for flying.

These engines also seem to like the Master Airscrew K-series props more than the lighter APCs

Although my TT91FS is slightly louder than my Saitos, it's still a very quiet motor -- to the extent that it simply doesn't sound loud enough to be scale in my P51. For that reason I've just ordered a Perry pump and will be fitting a straight pipe to the exhaust.

If yours sounds too harsh it might be running too lean and detonating -- or you might even be getting valve-bounce with that tiny prop.