I have a number of Ryobi, Poulan, ect engines converted to RC airplane use. I have made some straight pipe exhaust systems that have added 500+ RPMs over the stock mufflers. I would like to add a tuned straight pipe to maximize the high end (my current pipes are just cut to a conveninet length). Does anyone have experience with this? I don't know how long the initial pipe should be before starting the cutting to length trials. I would like to eventually make a pipe that can be reduced in length by simply sliding one snug fitting pipe over another. My calculations indicate that at 6000 RPMs a quarter wavelength pipe would be over 30 inches long...A bit long to handle conveniently. Anyone who has done this can maybe set me straight and tell me, hopefully, that I am wrong and a much shorter pipe will work. The adjustment range would be good to know as well since I plan to make the adjustable systems once I have the parameters figured out.

Thanks

An open pipe should be short like about 4 - 6" !
Too long, and the engine will loose all torque at higher rpm. Longer pipes need to be plugged at the end and have a small exit hole added.