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Old 02-29-2012, 10:43 PM   #74 (permalink)
Olympiadis
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Quote:
Originally Posted by E4ODnut View Post
Having said that, and emissions concerns aside, I see no reason why conventional gasoline engines can't get improved BSFC at lower engine loads by leaning the mix, adjusting spark timing to suit this leaner mix, and opening the throttle somewhat to maintain the required power. The larger throttle opening will reduce pumping losses or what ever you want to call it, as well as improve the thermal loss. The exact cause of the improvement doesn't really matter, what matters is that the end result should be better low load BSFC.
Correct. Being a tuner, I have done this many times over the years.
You must use a wideband O2 as a reference. The narrow band O2 is unsuitable for anything but very near 14.6:1.
The key to any tune is the degree of control the tuner has over the ECM, - calibration and algorithm.
I have yet to use a M.S. system, but I would guess that you start out with a good advantage in the control department.
If you are able to re-define the load-cell matrix for fuel trims, then you can increase the tuning resolution in your sweet-spot area of your main fueling table. This will help greatly with running lean but quickly adding fuel to cover additions to load while driving normally.
You will find that when cruising near the lean-limit, that even a small amount of added load can cause surging and/or spark-knock (not the same as detonation).
Most cruising occurs in a fairly narrow band in your fueling table. If you can increase the resolution of the table here (increase the number of cells), then it will make your tuning work easier.

Many of the wideband O2 sensors, like ones from Innovate, can simulate a narrow-band output signal in a fashion that is skewed to the tuners desire. This allows your ECM to perform the adaptive fueling algorithm without major issues.
Since I don't work with M.S. I am unaware what the system can handle in that area.

Those tuners who insist on adding the maximum amount of spark advance while running lean both make their job of tuning for smooth operation harder, and end up negating much of the fuel mileage gained from running at the leaner AFR.

If you watch your wideband closely and have the ability to change spark advance values in real-time, then you will see that advancing the spark has the effect of leaning the AFR as read on your gauge. Most people assume a leaner burn in the chamber when in reality the fuel delivery has not changed.
The idea is to work towards the lowest injector pulse-width that you can get away with while maintaining a given speed.
Don't go into it trying to work towards the most spark advance or the leanest reading as seen on your wideband gauge.
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