I have to disagree with most of what is being said on this thread. I raced glow powered boats for years, all with tuned pipes. Tuned pipes are tuned for what you want. In general the longer the pipe length, the more torque you will get. The shorter the pipe, the more top RPM you will get. If you get too short you lose your torque and the engine won't be able to get going. This is not even considering the design of the pipe. Some pipes such as an Irwin, give tremendous low end power. A Mac pipe is more for top end. A pipe is not useless for 3D. They will all help in the transition and allow you to turn a bigger prop. Just don't get it too short or you will have the engine jumping on and off the pipe, which is no good except for top end. A tuned pipe is always working. When I talk about length, I'm talking about from the glow plug to the high point of the pipe, not the length of the pipe itself. I hope that makes sense. I have used pipes on 46 powered profile planes and they do help all through the throttle range. This has been on stock motors.