Padelis,
Check this web sites. I suggest that you get a pipe design around the engine. I don't think the 4 cycle or 60-90 pipes are good choices. If I were you, I will go Aeroslave or ES pipes with proper volume for the engine.
http://www.aeroslave.com/
http://www.rcpattern.com/2cycle.htm#1
Good luck,
Vicente "Vince" Bortone