Piet....if you want to try and coax low speed power from your engine
you will have to use a long headpipe. Lenthening the headpipe is for
low prm use.....longer is for low speeds.....set-up a "torque pipe".

You said the engines battles to "get onto the pipe". A pipe set for low
RPM will not give the type of RPM boost that is associated with an
engine "coming on the pipe"....at which time the engine will jump into
a higher RPM range, and much more power will be produced. This jump
can be 2,000 RPM, or as much as 4,000 RPM.

I Have an OS .61 engine set for low RPM with a long head pipe, the blue
plane....at 11,400 RPM. I have another engine, an OS .90 that will be set
for higher RPM....at around 14,500 to 15,000 and greater speed than stock.
I will probably have to cut off the headpipe to get the system where I want it,
but the engine on the white plane will "come on the pipe" when I tune it to do
so. When it "comes on the pipe", it will jump from a normal RPM of 12,500
to 14,500 or so.

I will be using probably a 12-7 prop on the .90 engine. The .61 engine uses a
bigger prop....a 12-8.

FBD.