As I recall ignition timing as high

as 27 + degrees BTDC has/is used for naturally aspirated rotarys.........Lynn has stated

many times that 20+ degrees BTDC is actually plenty for most use and not much more

than that probably should be used for our turbo engines............Again Lynn jump in here

and give us the straight info..............  

I just checked my Racing Beat manual again, as the memory is fading a bit. They use 10 degrees on the dyno and race on 12 degrees for turbo and supercharged engines. Keep in mind that they are pouring fuel through this engine to make max power, and are fuel cooling it to the extent possible.

 

Turbo and supercharging gives away the Ace in the hole owned by the rotary. And that is the big (much area) cold combustion chamber, that allows the use of very low octane fuel without detonation.

 

So now we add the turbo, and the turbo adds 100 degrees to the intake air and we take one giant step closer to the detonation penalty box. Detonation is charge temperature dependant, and now the plan is to run at least 100 degrees above ambient all of the time?  It is just a degree of difficulty problem. Turbo engines are run lean of peak EGT every day.

 

Where the NA engine is loosing compression ratio as the RPM goes up, the turbo engine is gaining compression ratio as the boost goes up. The when boost is at its limit, cylinder filling and compression ratio starts down again. Probably above where the engine will be used.

 

The transition from rich of peak climb to lean of peak cruise is critical. I would let the speed build up so the switch to lean of peak can be with the engine unloaded a bit. The loss of fuel will slow the plane and a few seconds of lighter load will help the tuning time. Both situations could have been loaded into the controller and once at speed the switch to "B" would be all that is required.

 

Switch to "B", lean to stumble, back rich to just smooth.

 

Less fuel, less power, slower plane. BUT...........Lower cost for fuel. Less wear. Lower temps. Less worry.

 

Read everything about piston airplane turbo engines.

 

The Allisons in the P-38s were turbocharged and they did just fine.

 

Once lean of peak at cruise, lower chamber temps from lower fuel burn lowers charge temps.

 

Lynn E. Hanover