RE: Pipe length between engine and muffer
Better -simply because it is not sensitive to length.
For learning the "3D" stuff -you need smooth throttle response.
easier to do with non-tuned stuff.
Also - keep prop loads down- that is - let the engine rev-
largest prop-- a 26x10 Mejzlic- also try26x8-keep static rpm up in the 6000 range.
It takes practice to get comfy with a model hanging on the prop all day (zzzzzzzzz)
and the engine is loaded far heavier than when actually flying thru maneuvers at speed.
The heavier the model -- the smaller the prop .
Somewehre between 24x10 and 26x10 , you will fing a combo you like for 3D
On my IMAC plane - I can run the 27x10 stuff - no problems as the engine is unloaded most of the time.