<< Lynn,  how did you tune your p ported
 > race car.  Did you try different runner lengths?  What advice can you
 > offer?    Thanks  Jerry
  >>

The factory Pport has about an 8" runner length. Good from 7,500 to 10,000
RPM.
Nothing useful for airplanes. A good length for street performance ends up on
top of the engine. So the over the top tubes end up close to a good result.
Better more attention to the bell shapes at the end of the runners than getting
the exact length.
You will be flying a dyno around anyway, so tuning will be easier than on a
street car. Max available power goes away rapidly with altitude. So WOT at
cruise will be 70% to 75% power with less stress on everything.

Airplane engines are rated in California HP. Rotary engines are rated in Ohio
HP. So a 145 HP rotary can outrun a 160 HP Continental piston engine. A
Cessna 150 has how much HP? about 150? Wrong................it has 79 HP.

You cannot turn the engine to its HP rating RPM with a prop on it.

The exhaust tuning has a more profound effect on power that does intake
tuning. This is on the old style engine the new one is claimed to have no overlap
and this may not be the case. The older engines have a bit of the effect stock,
even though mechanically they show none, the exhaust dilution is there even
at speed. And if ported at all will collect more overlap and become more
sensitive to the exhaust system tuning. Two primary runners of exactly equal length
and a smooth collector. After that it is just as low a back pressure as you
can stand, gets the Max power. The builders do chase that last few horses with
spacer changes in the inlet tract, but with a poor exhaust system it matters
not at all. So the exhaust will be more restrictive than ideal. Ideal will be in
the 108Db range and that is just too loud. The Mistral lashup shows what seem
to be too long a runner but it seems to work just fine. A good place to start.

Just some ideas.

Lynn E. Hanover

 
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