Quote:
Originally Posted by PeteKz
Chris, you are correct about AFRs and how they vary, depending on fuel mix.
For 10% ethanol contamination, stoichiometric is about 14.13. That's why I prefer to display lambda. However, AFR in the 11 and lower ranges that the dyno print out showed is way too rich, even for preventing detonation.
Per Bosch, best economy lambda is 1.05, and best power is 0.90. Going rich to 0.85 provides additional cooling and prevention of detonation. More than that wastes fuel and loses power. For 10% ethanol/gasoline, lambda 0.85 is about AFR 12.0.
One other fine point for everyone to keep in mind: The "AFR" usually is not measured directly. Instead, an O2 sensor is used to measure lambda, and then a multiplier is applied to compute AFR. Thus, if you are running a 10% ethanol contaminated fuel, and the lambda is 1.0, the AFR meter/printout displays 14.7, even though it's really 14.1.
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Yes, basically a quote from my reference in post #17,
"Automotive Handbook - Second Addition", Bosch, 1986, pg 439, ISBN 0-89883-518-C
A key point of this thread should be that once the AFRs are near optimum, more significant torque improvements typically result from tweaking ignition maps, not withstanding detonation.
This doesn't imply, though, that ignition tweaking may not be detrimental. Without knock control, a high load, high temp, and/or low octane fuel are problematic with an excessive timing advance.
The issue of detonation is not easily simulated/determined based on "dyno results".