AFR and E85
 

FT86, I have a bugging question.

What is the AFR I should see in the gauge with E85 at WOT?

I have seen this question posted in many forums but instead of a direct answer, I see people dodging the question.

When we talk about 93, I think we can all agree the sweet spot is between 11 AFR (borderline before rich) to 12.5 (borderline lean).

What is that window when running E85?

@FA20Club.com @mad_sb

OK, so the difficult thing for people to wrap their head around is this: air fuel sensor measure lambda, which then gets converted to the AFR scale of your choice. The stoich point for gasoline and Ethanol are very different but because the air fuel sensor will report each fuels stoich point as lambda 1.0 which gets converted to gasoline afr in most cases your stoich point is still 14.7:1 on the gasoline scale.

So,
E85's Lean Best Power is Lambda 0.8673 or (14.7*0.8673) 12.75:1 on the gas scale
E85's Rich Best Power is Lambda 0.7143 or (14.7*.07143) 10.5:1 on the gas scale


E85 will tend to knock on the rich side more so than the lean side. I would think 11.5 would be a good place to start with boosted applications and move a little up or down depending on the tune and what the car needs to be happy.

There is no exact answer though because it will depend on ignition timing, boost level, turbo efficiency, etc etc etc. Over all I would think a little bit leaner than pump gas on a gasoline calibrated wideband.

What about E85 afrs for non boosted cars?

Ok let me get this straight. The O2 sensor reads lambda, which at 1.0, is measuring the stoich point for whatever gas you are using. It then considers 14.7 AFR as lambda 1.0 obviously again regardless of fuel.

Then using your conversion we get the max lean max rich figures converted to AFR for E85.

What are these lambda values for 93 pumpgas? THANKS for the help!!


Edit: I think I'm starting to understand this a bit more. So the REAL stoich point for E85 is not 14.7 AFR but 9.765 AFR. So if I were to want to know the real AFR for E85 when my gauge is telling me 10.5 right now, I would multiply .7143 lambda* 9.765 (real E85 stoich AFR) and that would give me 6.97 AFR. That is the REAL AFR, but since our gauges are calibrated for pumpgas, it will show .7143 lambda *14.7AFR = 10.5 AFR

Exactly right!

It's just easier to talk about gasoline AFR since everything uses that by default :) Or if you have a dedicated wideband you could just set it to lambda and not worry about afr :)

Again it depends. I would say shoot for the leaner side like 12.5. I have only tuned one car on E85 so far, and that is my own. In theory, since E85 is oxygenated, the more you put in the cylinder the more power you can make so long as your in the range of best torque so next time out I may try richer, the main thing is you have to tune for MBT on E85. You can very easily exceed MBT when NA on E85, not so sure about FI.

With E85 there really is no one right AFR to run as it works in a huge range unlike regular fuel. Add on top of that Direct Injection and it will really mess with your head. If you are reading in gas AFR 17:1-10 which is a much larger range then fuel which is about 15:1 to 10.

You will often run as rich as you can without misfiring for maximum power with boost since adding timing and boost far outweighs the gains you would get from leaning out .5 AFR.

The OEM ecu strategy relies heavily on the port injectors at high RPM so you end up with traditional AFRS while tuning 11.5-12.5 AFR but with the Hydra EMS we have more control on the ratio of direct injection to port injection and I was making the most power with AFRs reading off the chart lean. It wasn't actually lean however :lol:..I know confusing
A very rough novice guide is to just add +1 to your gas AFR so if you cruise at 14.7 on fuel you can run 15.7 on E85 and if you tuned your car to 11.0 on gas you can run 12.0 on E85.

If you're a pro forget all that and just run as lean as you can get away with under cruise and whatever makes the most power under full load :thumbsup:

Thanks,
Phil Grabow

Sadly the stock ECU will not let you target anything leaner than 14.7:1 while closed loop.... at least not without a code patch. That was one of the first things i wanted to play around with on E85. 14.7 equates to 0 on an 8bit data value.

You can be like the kool kids and switch your AEM failsafe gauge to lambda.

YAY!!!


http://victorsvillage.files.wordpres...y-for-hiro.jpg

Oh how unfortunate ;)

I'm got my Hydra EMS FRS running at 16.5:1 in light load cruise areas. It will feel a little "flat" at those AFRs so I do richen up as load increases but it really helps to close down the fuel economy gap between fuel and ethanol. I run two separate closed AFR targeting tables in my map, one for pump fuel and one for E85 so when I run pump gas I don't have to change my closed loop fuel targets. Each fuel has it's own closed loop fuel control maps.

It will run perfectly fine at 14.7 but fuel economy won't be maximized.

Totally awesome! Stepping off soap box now :)

mines at 14.7 ish when driving "like a average person" lol but wot when i have e85 im at like 11.01-11.68 :) and have a little nice flame at the end :evil:

I have no idea what mine are I did take one log though before sold my cable. yes I need another. This thread is win.

mine reads 14.3 at idle (stock ECU reads 14.7)
at WOT it reads 11.8 (stock ECU reads 12.1)