E85 Timing for Compression Ratio & AFR
 

Hello,

I want to get the most HP from my 2012 Silverado FlexFuel 5.3 Aluminu Block. It has intake, Longtubes, 3 inch piping, 410s and internals are stock.
I have been making adjustments to my tune. Right now I am at 9.6:1 Compression ratio running E85 which was tested at 50% alcohol (E50). AFR is at 11.2 at WOT. My timing at WOT starts from 20deg and goes up from there up to 31 deg at 6k RPMs. Is that good timing for running E50?

Also I did some Data logging, and before I had Spark start at knocks at 3.5deg so I retarded 4 deg and now I get no Knocks at WOT.

If you are still using AFR based on the gas scale, then 11.2 is really rich for E85 and no boost. You should be able to run 12.5 AFR easy just like regular 93 octane. I'd say you are losing power going that rich.

Or just command .85 lambda.

Wouldnt that be a little lean for E85?

The opposite because this is still a NA engine using the GAS scale for E85.

NA engines prefer 12.5 to 12.8 afr is most applications. A Boosted engine around 11.5 as a ball park.

E85 is like adding an intercooler, the fuel has a superior cooling effect over gasoline as the fuel evaporates and allows you to run even leaner than 12.5 AFR. Some can get away with 13.0 on E85 because of how good it is.

Ethanol benefits from a much wider range of torque production in terms of air to fuel ratio. With ethanol, anything between 11:1 and 12:1 on the gasoline scale will be basically indistinguishable unless you are timing limited. However, on the same scale, ethanol peak thermal efficiency is at a point richer than that of gasoline. This point will dance around as you vary spark and CR, but for your purposes, it needs to be richer than gasoline...I wouldn't target any leaner than 0.82. Running leaner might make you think you are conserving fuel, but for the same spark timing your cylinder air mass will have to increase disproportionate to the increase in lambda to maintain torque output.

So that means that I would have to lean it out to .082 Lambda and I would get good Torque and HP and still be safe? The timing seems to low to start at low 20s deg at WOT.