AFR for max power

[edfiero1]

I seem to remember reading that Stoich for E10 Fuel is something like 14.3 rather than 14.7.

Does blend of fuel have any implication for what AFR to target in PE mode for max power? For example, is the typical target still 12.8 if running E10, which most gas is now days or E85 for that matter?

[Fast355]

I seem to remember reading that Stoich for E10 Fuel is something like 14.3 rather than 14.7.

Does blend of fuel have any implication for what AFR to target in PE mode for max power? For example, is the typical target still 12.8 if running E10, which most gas is now days or E85 for that matter?

12.2 is where I shoot for

[RobertISaar]

different engines are going to like different AFRs for max power.... chamber design/mixing is going to play a significant role in what AFR an engine likes best.

[Xnke]

In most engines, maximum power comes around 13.8:1 with non-alcohol gasoline. The higher the chamber pressure, the richer the mix can be before you start loosing power.

I tune my engines for 13.8:1 AFR N/A, and push that down to 12.5:1 under moderate boost, say 8-12lbs. The richest point on the VE map is going to be the torque peak, and once you've revved over peak torque, you can add back timing and pull back fuel and KEEP making power. For most 2-valve engines, this is what has worked for me. 4-valve engines, not so much-they have wanted to see 12.8:1 to make max power, the few that I have done.

For example, I see peak torque in my L28 at 5300RPM, at that point I'm pushing 12lbs of boost and the engine revs to 7200 before the shift. In order to keep the torque curve fairly flat, the AFRs go from 13.8:1 through most of the N/A areas up to 13.2 when I get into boost, 13's up to about 3lbs of boost, 12.8 up to about 6lbs, then 12.5 through the torque peak. Over the torque peak, I start pulling fuel back, till at 7200RPM I'm still at 12lbs of boost and the mixture tapers back to 13.2 and some timing comes back in, from 5300RPM to 7200 RPM under boost it picks up 2.5 degrees of timing.

This is the kind of tuning you MUST do on a load-holding dynometer, if you try to work out the details like this when you can't hold it at a steady load you're really just throwing darts at water balloons filled with nitroglycerine.

[edfiero1]

different engines are going to like different AFRs for max power.... chamber design/mixing is going to play a significant role in what AFR an engine likes best.

Yup, understood. But my original question remains... for a given engine how much does the fuel play into, IF AT ALL to what AFR ratio makes max power (excluding any knock consideration)?? If a given engine made max power at 13.0 on pure gas, would running E15 or E85 change the target AFR? (I know VE tables need to change, but my question is regarding the target AFR.)

[RobertISaar]

yes, fuel composition will change the AFR that peak output is achieved at. it would be easier to think of it in terms of lambda, as that should hold fairly constant for gasoline-based fuels. once you get into other fuels that have vastly different burn rates or energy content, then conventional gasoline-based rules don't necessarily apply. but comparing E0 with E10 or E15, you'll find that the ratio that stoich drops by will be about what you'll want to drop the AFR when in power enrichment as well.