I wrote this on another forum, and thought I'd post it up here for feedback, since we all know h-t has the most educated people in the world.. Anyway, I'm just trying to figure out some theory behind running leaner than stoich for fuel economy. Here goes..

My whole thesis on this is basically extrapolated from clues certain tuners on h-t have been dropping for a while. When a tuner says that you can get better mpg from running leaner than stoich with more timing, that got me thinking. I didn't see how taking out fuel past 14.7 for a given map point would give you more power. As far as I know, it doesn't. So then I thought, wait a minute, maybe I'm not seeing the big picture. The point of tuning for part throttle is to get the most energy out of every pulsewidth, not out of a certain amount of air. So if it's more efficient, why not put that pulsewidth on a higher manifold press part of the map? If you have a vac/boost guage in your car, you know that at a certain cruise speed, your guage will have a certain reading. But what I am saying is totally counterintuitive because with what I'm describing, the guage will actually read a slightly higher manifold press, for the same cruise speed, yet the motor is actually using less fuel, since at that higher map press, the pulsewidth is able to generate more power, so you end up with a slightly shorter pulsewidth to achieve the same cruise speed (power). Most people would see the higher manifold press and assume that the motor is under a higher load/must be putting out more power, but it isn't. It's just running leaner with a very slightly shorter pulsewidth.
Thing is, how do you tune this. With tuning part throttle for a given manifold press, you just add/subtract fuel and timing until you're at the most power. Oem maps just put the fuel at 14.7 and put the timing either where it's safe or at mbt, if that's safe with the available fuel. But when tuning leaner than 14.7, you essentially have 3 variables at once coming into play, so it's not so simple. I was trying to eliminate one of the variables by describing the scenario of moving the certain pulsewidth up and down on the map scale.

Here's some real "food for thought". What is the advantage of drive by wire? (computer controlled throttle)....

If any of this is incorrect, if you do actually get more power for a certain map press by running leaner than stoich, I don't understand how that would be, if you know, please explain. I believe that you would get a lower bsfc (mpg) by running with more air because it increases the motor's dynamic compression. That is why diesels are more efficient than gasoline motors, they have a much higher mechanical compression ratio and don't have a throttle, so their dynamic compression is much higher. The btu content difference in fuels is minor in comparison.

Anyone want to share their knowledge or experience with tuning part throttle for mpg?