I've been tweaking on my e85 tune to get the AFR flat and find the "right" ignition timing. However, I think I'm having an issue with fuel compensations. Does e85 require larger IAT compensations? The temp dropped about 20 degrees F over the past 2 days, and my AFR at WOT went more lean even though I was adding fuel to make it richer. I can't think of any other reason why the mixture would go lean despite me adding more fuel.

BTW, does anyone know what the estimated increase in ignition timing would be between E10 and E85?

 

Its possible you don't have enough fuel pressure or fuel pump to keep up with the demand. I highly recommend a Walbro if you're going to play with e85

 

I may run into a fuel pressure issue with the stock pump, but I believe that would show up in my graphs. If the pump wasn't able to keep up at high RPMs, I would expect to see it go unexpectedly lean up top only, but this is happening pretty evenly across the whole RPM range. My overall torque curve still follows the injector pulse width curve pretty well. I suspect once I get the fuel curve very flat again, it will probably match my torque curve just as well as it did on E10.

BTW, I found some other car threads about E85 and fuel compensations. It seems that it is common for E85 tunes to run lean when it's cold and rich when it's hot. I'm going to increase the slope of my IAT fuel compensation curve to see if that helps.

 

[QUOTE=gernby,Sep 25 2010, 08:03 AM] I haven't tried e85 yet, since I just installed the new injectors last Sunday.

 

you are not going to find the right ignition timing on the street. you can get close though. it's not going to be a dramatic difference from where ever it was on pump gas. if you were not able to reach mbt on pump gas because it would knock before you were able to reach mbt then you would be able to run more ignition timing with e85 and actually hit mbt.

again, do this on a dyno.

as far as iat compensations, it's a case by case basis. if you're up north the e85 will vary with regards to the ethanol content. it varies in the winter and it will throw off your tune.

how have your cold starts been? lol

 

With the new injectors what is your duty cycle gas and e85?

 

It you keep going richer you get to a point where the engine stops burning all the oxygen and the AF meter starts to read lean even though the mixture is actually way rich. This especially happens if the mixture are rich enough to so the spark starts to go out.


I tuned my 13.8 compression race motor on E85 and found the richer I went the better the power. I was getting into the mid 11:0 AF ratios. (calibrated for gas).

I'm told the way to tune E85 is to use exhaust temp thermocouples in the headers. The exhaust temp starts dropping when you have started making it too rich. All the extra fuel is doing is cooling the charge even after its burnt.

 

I was going up to 90% with 93 octane gas with my stock injectors and an AF of 11.9 and AF Corr of 13.3. The bigger injectors brought the duty cycle down to 46% with an AF of 12.4 and AF Corr of 13.6. My current E85 tune gives a 63% duty at an AF of 11.75 and AF Corr of 13.2.

 

I think I'm getting very close to optimal timing using my soft dyno. Once I had my fuel curve flat, I just kept raising the whole ignition map 2 degrees at a time until torque quit going up. When I overlay a graph of torque / fuel, I can see which timing gives the most power for the same amount of fuel. I didn't get ANY knock counts, and power was very smooth.

I believe that if I create another timing map using the values from the circled sections below, I'll have a pretty optimal curve, right? I figure I'll just take the average value where the curves are all equal.

 

Maybe I'll try leaning it out a bit, just to make sure I'm not running way too rich. Thanks for the info.