Brain dump from an experiment I performed in 2008-ish:
I spent some time on the dyno today, I did not do any power tuning, I was doinjg an experiment to find the best AFR for economy with timing optimized for that AFR. (ALL AFR's noted here will be on the gasoline scale even though i was using E85, which at this time of the year here is supposedly E70).
I logged my rpm and load at about cruising speed on the highway at 3000 rpm fith gear , so that i could go to the dyno and then get an idea of my HP required at cruising speed.
I went to the dyno and loaded the car to my cruise conditions, and noted the tractive effort (say 30 lbs).
I then loaded the car at this point at different AFR's and then exoperimented with the timing with fixed AFR until i found the timing that used the lowest msec of fuel while still making 30 lbs.
I repeated this for different AFRs.
The results: (only listing the least efficient tested to and the most efficient)
3000 rpm, 30 lbs tractive
manifold kpa=about 55 for all
AFR 15,best advance=28,msec required=2.27
AFR 16.8,best advance=40 ,msec=2.07
i experimented past 17:1 and between 15 to 16.8, but 16.8 was the best
timing seemed very critical 1 degree either way lost 3 lbs or so tractive force.
i did not do any power runs , but generally it supposed to be less timing needed for e85 because it burns faster than gas,however because of the octane rating less retard is needed under boost,and it seems you can run alot leaner...? so in a nutshell the theory is you can run less timing until you were knock limited in your gas tune, but then you may be allowed more timing than in the gas-knock limited areas under boost. That is to say mean best timing is less with e85, but less retard is needed to prevent knock...this is the theory anyway it will be maybe 6 months until i do a similiar test for power tuning.
Right now i am mapping my engine as TPS/LOAD this way I can target economy or Power AFR dependent on TPS postion (driver intention) rather than just load. For instance on highway cruise and a moderate hill you may near 100% load and would rather target leaner, beacase you are just trying to maintain cruise, not accelerate, When at other times you are at the same load site but want max acceleration. by putting "wrong" values in the fuel table at less than 100% TPS you can have econmy AFR's, yet when you go to 100% TPS it can target best torque AFR's. On the Sm2 one has to compromise on the ignition advance because that is only load/rpm based. The SM4 would be nicer for this...
if you study the ethanol line between about .85 -1 FAR you can see that it is linear. This makes me think that that the difference in BSFC for any FAR/AFR in this range will be nearly the same.. Because less fuel is used when leaner,but more timing advance will be needed therefore more negative work. However because you will also have to open the throttle further to ingSeest the same BTU's worth of fuel, pumping losses will less on the leftmost end of that linear range.