RE: Yet another DDUST take II
i still think an 8x8 is too much prop for a 34 sized engine. My 36 currently has a 9x6 on it, and for a speed plane, thats a good deal of prop. I think 8x7.75 is a typical 40 size pylon prop - and, while the engine is fairly stout, its not going to keep up with a 40 size pylon engine. Therefore, i'd think that the 8x8 is just a bit much for max power. The other consideration versus a boat engine and an airplane engine is the difference in the rpms- the lower the rpm, the longer the total pipe length will be.
Cutting the pipe for max rpms is a good idea, doing so while overpropped will probably result in a header thats just too short.
You can always try it with the factory mufferl and see what your turning, and decide from there if the pipe is close to being tuned properly.
I'd think you'd pick up at least 1000 rpm with the pipe over the stock exhaust.