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My research indicates that an air/fuel ratio (for gasoline) of approx 12.65 is referred to as "Best Power". A lesser A/F ratio (13, 14.7, 17, etc) will fail (theoretically) to burn all the oxygen available in the mixture therefore leaving power on the table (had you put in sufficient fuel to burn). However, I have also read that too much fuel (A/F < 12.65) is counterproductive as you then tend to use BTUs to vaporize fuel that can not burn due to lack of sufficient oxygen. Some mixtures have more fuel than the theoretical optimum as the fuel is used to "cool" and prevent detonation.

FWIW

Ed Anderson

----- Original Message -----

From: Russell Duffy

To: Rotary motors in aircraft

Sent: Thursday, January 13, 2005 3:20 PM

Subject: [FlyRotary] Re: I got the power !

If I recall correctly, the
air/fuel mixture number was somewhere around 13... Make any sense?

Yep, sure does. The theoretical ideal air fuel ratio (AFR) is 14.7, but that doesn't mean much to us.   Any number lower than that is richer, and of course higher numbers are leaner.   Max power mixture is richer than 14.7, and I'd suspect it might be close to your 13, but I'd also bet that it depends on lots of other things as well.   During lean cruise, you will likely see numbers way up in the teens.

My old FD had a Power FC computer, and a wideband O2 sensor. I had it tuned to around 11 AFR for full throttle, full boost, around 14-15 for normal cruise, and I could even see the max of 20 on very light throttle cruise.   11 AFR is pretty rich, and is needed to avoid detonation with the turbos, but it shouldn't be needed for a NA engine. Bottom line is that you'll have to do some testing to finish setting it up.

Rusty