In a message dated 3/5/2011 1:17:37 P.M. Eastern Standard Time,=20 keltro@att.net writes:

As I recall ignition timing as high

as 27 + degrees BTDC has/is used for naturally aspirated=20 rotarys.........Lynn has stated

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

than that probably should be used for our turbo engines............= Again=20 Lynn jump in here

and give us the straight=20 info..............

I just checked my Racing Beat manual again, as the memory is fading= a bit.=20 They use 10 degrees on the dyno and race on 12 degrees for turbo and=20 supercharged engines. Keep in mind that they are pouring fuel through this= =20 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.=20 And that is the big (much area) cold combustion chamber, that allows the= use of=20 very low octane fuel without detonation.

So now we add the turbo, and the turbo adds 100 degrees to the intake= air=20 and we take one giant step closer to the detonation penalty box. Detonatio= n is=20 charge temperature dependant, and now the plan is to run at least 100 degr= ees=20 above ambient all of the time? It is just a degree of difficulty pro= blem.=20 Turbo engines are run lean of peak EGT every day.

Where the NA engine is loosing compression ratio as the RPM goes up,= the=20 turbo engine is gaining compression ratio as the boost goes up. The when= boost=20 is at its limit, cylinder filling and compression ratio starts down again.= =20 Probably above where the engine will be used.

The transition from rich of peak climb to lean of peak cruise is crit= ical.=20 I would let the speed build up so the switch to lean of peak can be with= the=20 engine unloaded a bit. The loss of fuel will slow the plane and a few seco= nds of=20 lighter load will help the tuning time. Both situations could have been lo= aded=20 into the controller and once at speed the switch to "B" would be all that= is=20 required.

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

Less fuel, less power, slower plane. BUT...........Lower cost for fue= l.=20 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= =20 lowers charge temps.

Lynn E. Hanover

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