James,
I've been doing some experimenting with different props on my Excelleron and found
the 3 and 4 blades are much quieter than the 2 blades. It might take some trial and
error to find the right size for your plane and keep acceptable performance but the
noise difference is very apparent. It surprising how much engine noise comes from the
prop.
Don Szczur , who won our national championship in FAI a couple of years ago , used an
ES Composites carbon fiber pipe on a YS 140DZ that was made for a 140 2-stroke. He
said the performance was as good as the 4-stroke pipe but it was the quietest pipe he
had ever used . The only issue might be fitting it on the airplane as it is somewhat
longer than the 4-stroke pipe.

Good luck,
tommy s