Quote:
Originally Posted by Enki
I don't fear lean mixtures; every one of the tunes I ran on my car utilized it; there's just diminishing returns past a point where you wind up giving more throttle to maintain the same speed and as a result the fuel consumption doesn't drop any more. I found this to be 15.5 AFR on my car, while others run their cars as lean as 17:1; somehow, I still have the best miles per tank on a mix of ethanol vs anyone on pump gas and leaner mixtures.
The only thing I'm "afraid" of is people bolting a turbo on to their car expecting one result and ending up buying a new engine because their understanding of how it should be done is incomplete.
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The thermodynamic conditions are such that you produce the exothermic oxidation of nitrogen. This is why you get elevated temperatures in this AFR range. At about 18:1 AFR and beyond, you see a significant drop in NOx production and a resultant drop in combustion flame front temperature. Hot NOx is highly corrosive and erodes valves and rings quite rapidly.
Throttling losses are your enemy. Driving with the throttle as wide open as possible is the goal of lean burn. If you can get past about 70-80% throttle opening you will have some power underfoot to vary your cruise somewhat and retain most of the benefits of minimal pumping losses. A turbo only helps by providing additional turbulence and heat. Yes, you will reach a plateau based on your current variables, and that is when you need to start changing those variables. If your engine management doesn't allow you to advance your ignition enough, you will have to increase your intake temperature and use lower grade fuel. Yes, lower octane fuels that have a tendency toward pre-ignition are preferable for very lean burn situations. Studies are even using diesel as an admixture.