Quote:
Originally Posted by 1slow370
Actually it's not how it works, lean fuel mixtures do not make the engine run hotter because there is less fuel vaporizing and sucking heat out of the motor, it is because a lean mixture burns more rapidly which means peak cylinder pressure is reached earlier in the stroke forcing the engine to fight itself while retaining a hotter mixture of gas in the engine for a longer time, in a rich burn situtaion the fuel will still be burning exiting the engine which tends to increase egt's but is not as hard on the engines cooling system. the latent heat of vaporization is less important until you start getting into alcohols and nitro mixes that really can cool the entire top end of the engine just by evaporating.
As for the closed and open loop stuff, what you are suggesting is already in place in the ecu, from the factory the car tapers from the low load sites which are 14.7ish and as load and rpm increase the afr tables drop in the ecu. If tuned properly your tuner should only be adjusting the mid and high range/load sites to keep it rich enough to prevent detonation, the low end only basically needs to be tweaked to fine tuned for changes in maf size. As seb had said in his earlier post if you were running 10.5-1 at idle that wouldn't be a good thing because it shouldn't be doing that. The only other time the low load sites should go richer would be if there is a tip in lean issues that can't be tuned out some other way.
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I think we are talking past each other, and not being very accurate. I have only been talking about closed loop mode (i.e. targeting a stoich mixture of 14.7:1).
First, the relationship of flame speed versus AFR is a curve that peaks below 14.7:1 then drops on both ends. So, while moving to a leaner ratio from a very rich ratio will speed up flame speed, that only holds true to a point around 12:5:1. After that, leaner = slower. I was talking about ratios above 14.7:1, where additional air will slow the flame speed down, and not speed it up as you suggest. See, for example, discussion here:
Spark Timing Myths Debunked - Spark Timing Myths Explained:: Application Notes ("At about 12.5 to 13 air-fuel-ratio the mixture burns fastest. A leaner mixture than that burns slower.")
Also see the same concept in graph form:
Or here:
As for the lean burn on cruise, the car is targeting 14.7:1 in closed loop, cruise mode from the factory. People have experimented with "lean tuning" i.e. targeting higher than 14.7:1 in closed loop, cruise mode in order to increase fuel efficiency.
For anything under load, I am not about to try to go a bit leaner than what my turner suggests to save some fuel. That extra fuel helps with cooling, which helps with knock prevention. I would rather save my engine.