ORIGINAL: on pipe
A greater pipe length is needed, to be tuned for the lower RPM, the engine is capable of reaching on its own. -quote
...So once I get this thing peaked out at its highest RPM, the pipe needs to be lengthened some more to keep it from going
lean in the air, right?
Ross,
This would be the end result.
If an engine is leaned to peak, while it is off-the-pipe; when it gets on-the-pipe, its fuel needs skyrocket and the leaner mixture results in earlier ignition and faster burn, which results in pre-detonation, which is the essence of a lean-run...
In an R/C plane, the pipe must actually be set so the engine would be on-the-pipe, when on the ground.
The pipe must be just long enough so the engine will get on-the-pipe, on its own, as the throttle is advanced in static conditions.
The higher flight RPM will still be within the tuned RPM range of the pipe, so you will lose only a couple of hundred RPM.
In other classes, like C/L F2D, speed records are broken by engines with pipes set to go on-boost only in during high speed flight...
You can actually hear the engine run erratically rich... until it comes on-song - 35-39,000 RPM song...
Do the break-in with a 1" smaller diameter prop and you don't really need the engine to get on-the-pipe.
The smaller prop will allow it to spin at the same RPM rich.
Don't even think of adjusting the pipe length, with an engine that has not yet been broken-in.
A great break-in technique that will bring the engine to top condition, is illustrated in [link=http://www.rcuniverse.com/forum/Tapered%2DBore_Engine_Break%2Din_%2D_Upgraded/m_1850473/tm.htm]this thread[/link].