Originally Posted by
kevinsburns
Tuned pipes don't turn on and stay on, they have low and max rpm ranges.
The short pipe is for low end power. A short pipe is short so the sound wave has a shorter distance to travel back to the engine so a short pipe will come on at lower RPM and turn off sooner too, top end suffers because the short distance and higher RPM the pipe becomes ineffective and out of time/tune.
A longer pipe the sound wave takes longer to get back to the engine thus the pipe comes on at higher RPM and stays on longer, low end suffers because the longer length is out of time/tune for the lower RPM.
Short is low end power good for short race courses
Long is top end power good for long race courses where you wouldn't want the pipe to pipe out too soon.
Back in the day we had pipe sliders that adjusted the length in sync with the throttle. Off throttle the pipe would be at the shortest length for low end power, and as the engine was throttled up the pipe would lengthen for top end.
Pretty much like the ceeva pipe someone else mentioned except the sliding pipe the whole pipe slid using a ceramic slider
Sealed, also a myth. The raw glasses that the sound wave forces back into the engine just before TDC hangs out at the exhaust port and never really enters the pipe, only the hot oil goes into the pipe so the sound wave doesn't care if it's sealed or not 100% the sound wave will force the glasses back in.
People do play around with the stinger to fine tune a pipe too. A pipe that's slightly larger someone will ventury down the stinger to help keep pipe pressure up to scavenge the hot oil from the engine.
You have it backwards. Short pipes are for high rpm and long pipes are for low rpm. The higher the rpm the faster the pressure wave travels. If load is too high (rpm too low) for the pipe length, it won’t get on the pipe. If the load is too light (rpm too fast) for the pipe length, it’ll get on the pipe early and fall off early. When tuning a pipe, usually one will start out long and work shorter in small increments until no gain is had. This is your ideal setting for the given load. Anytime the load is changed (prop size up or down), the pipe length must be changed. A lighter load will require a shorter system. A higher load a longer system. (Sometimes adding one or two sections previously removed can be reinstalled in the coupler to add the necessary length.
A friend of mine is a tuned pipe guru. I usually ask him his advice on a starting point for pipe length, but I know there are basic rules of thumb that will get you started. What those are escapes me at the moment.