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From: Lehanover@aol.com
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Date: Thu, 10 Mar 2005 01:57:53 EST
Subject: Re: [FlyRotary] Re: Mixture Settings
To: flyrotary@lancaironline.net
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In a message dated 3/9/2005 7:25:12 PM Central Standard Time, 
bob@bob-white.com writes:

<< Thanks Bill,
 
 So my belief that I need to run richer for the high power settings on
 the rotary is incorrect?  I have Tracy's EC2 so will have to set the
 operating mixture.  That reminds me, I haven't bought the bung for the
 O2 sensor yet (for the EM2).
 
 Bob W.
  >>
Looking at some dyno sheets, I think the point is that best power on the 
rotary is also rich of peak EGT. The sheet does not show peak EGT because there is 
less power there and that is not the point of dynoing the engine.

 Peak can get into the 1700 + degrees area and best power is well rich of 
that. The air fuel would be into the 14s for that EGT, and on paper for a piston 
engine that may be ideal for economy, even piston engines make best power just 
rich of peak EGT but just a bit rich of. 

It is a very bad idea to run that close to peak. Most manuals specify a rate 
of flow for takeoff power. This may be as high as 23 GPM for an engine that 
can cruise at 14 GPM. Look in a handbook. That fuel flow is well rich of peak 
EGT, and is not the correct mixture for best power. Best power is leaner (closer 
to peak EGT).

The piston engine needs the richer mixture on take off to slow combustion 
speeds to avoid detonation, and add a dash of fuel cooling. This also reduces CHT 
and exhaust valve temps. 


Here are two similar bridge ported 12As at best torque. This is much higher 
RPMs than a stock 13B.

TW1 
7,600 RPM 149.2 foot pounds. 216.2 HP. EGT-1 1478. EGT-2 1502. BSFC .656. Oil 
pressure 88.6. A/F 12.9. 

TW2
7,800 RPM 154.3 foot pounds. 229.4 HP. EGT-1 1518. EGT-2 1503 BSFC .666. Oil
pressure 99.8. A/F 12.3.

The NA engine is just about immune to detonation. So the good reason for 
lower EGTs is apex seal life. So there is no reason to go through Max EGT at full 
throttle. 

You could tune based on EGT, or 02 or a bit of both. Once at cruise you could 
flip to the other controller (Tracy's) and already be lean of peak. The EGT 
would just drop a bit without going through peak.

Just some ideas.

Lynn E. Hanover