I'm into 1/5 scale rc besides saws. There are a few good manufacturers that make expansion chambers and tuned pipes. Yes they are worlds better then a muffler mod. Saws dont typically have the room for them. With the right pipe you can gain significant filling of the cylinder via exhaust pulses. I think alx and rc maxx go up to 80 or 90cc engines, we just wish our saws had the power our rc engines do. Any way, bartolone, olimat, victory rc, alx, DC maxx, come to mind straight off. You can also look to the goped world and small 2 stroke dirtbikes and such for tuned exhaust as well.
This is a vrc tuned pipe on a 34cc ported and stroked zenoah (husqvarna) engine. Makes around 7hp.