AFR and E85

[bgibbsunc]

wow its funny I was just asking myself this question today and decided to search it and what do you know. lol So let me get this straight If I have a aem failsafe gauge and have it on AFR. On E85 how rich/low should it be going at wot.

[jamesm]

Originally Posted by bgibbsunc

wow its funny I was just asking myself this question today and decided to search it and what do you know. lol So let me get this straight If I have a aem failsafe gauge and have it on AFR. On E85 how rich/low should it be going at wot.

if you're n/a then probably no richer than 12.5:1, fi maybe 11.8-12:1. e85 works well over a much wider range of afr's than gasoline, so depending on who you ask you'll get a different answer. there are a wide range of opinions on the topic, but the generally accepted idea is that it's safe to run at least one full afr point leaner than you would on pump gas.

[reeves]

Originally Posted by Element Tuning

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

Just curious if any tuner has been able to maximize fuel economy on Ecutek by running slightly lean during very light crusing... assuming that is indeed safe to do with E85?

[cdrazic93]

Originally Posted by reeves

Just curious if any tuner has been able to maximize fuel economy on Ecutek by running slightly lean during very light crusing... assuming that is indeed safe to do with E85?

The nature of E85 is scientifically proven to be fuel inefficient. Running slightly lean on a pump gas setup to optimize fuel efficency, won't work on E85. More or less .1 change in milage...so from 14 to 14.1 mpg lol. The duty cycle required on the injectors is almost 2 times larger (last time I checked) than the duty cycle on a pump gas tune injectors IIRC, thus the need for a larger set of injectors if using a flex fuel kit or an E85 tune.

As a rule of thumb I always learned that turbo cars run more rich than NA cars. Turbo AFR's usually fall between 11-12 under WOT, and like others said, no less than 12.5 for NA cars. Besides that's a seriously rich AFR, and you're MPG will suffer from that. A better AFR for NA is probably 13-14.

[RickyB]

Originally Posted by cdrazic93

The nature of E85 is scientifically proven to be fuel inefficient. Running slightly lean on a pump gas setup to optimize fuel efficency, won't work on E85. More or less .1 change in milage...so from 14 to 14.1 mpg lol. The duty cycle required on the injectors is almost 2 times larger (last time I checked) than the duty cycle on a pump gas tune injectors IIRC, thus the need for a larger set of injectors if using a flex fuel kit or an E85 tune.

Gasoline stoich AFR is 14.68, E85 stoich AFR is 9.87, so if you hold everything else constant, you will need 1.48 times more E85 mass to run the same distance. Gasoline density is 0.7197 g/cc and E85 density is 0.7890 g/cc, so you only need 0.91 times the same volume of E85 to have the equivalent mass of gasoline. That means you need 1.36 gallons of E85 to go the same distance as a gallon of gasoline.

However, since E85 is much higher octane, you can run a more aggressive cam profile to produce a higher dynamic compression ratio while cruising and boosting without encountering knock. This increases engine efficiency, so now you can go the same distance with 15-20% less E85. The newest generation of flex fuel cars is starting to take advantage of this to bring E85 mileage closer to that of gasoline. The current version of the Hydra firmware under development will also let you adjust cam profiles based on ethanol mixture to take advantage of this.

Originally Posted by cdrazic93

As a rule of thumb I always learned that turbo cars run more rich than NA cars. Turbo AFR's usually fall between 11-12 under WOT, and like others said, no less than 12.5 for NA cars. Besides that's a seriously rich AFR, and you're MPG will suffer from that. A better AFR for NA is probably 13-14.

This is true under boost, but not while idling or cruising, so while this will certainly affect how long you can go at the race track, it has little bearing on daily driving. Manufacturers are now using smaller turbocharged engines to get higher fuel efficiency than larger NA engines would give.

[cdrazic93]

Originally Posted by RickyB

This increases engine efficiency, so now you can go the same distance with 15-20% less E85. The newest generation of flex fuel cars is starting to take advantage of this to bring E85 mileage closer to that of gasoline.

Wasn't about to look up those numba's as I have enough chem homework to deal with as is. Btw, you didn't keep your significant figures lol jk

Yes, the milage is getting better, but there's still room for improvement, so for now unfortunately it's not quite up to par with gas MPG. But then again, that's not why I would be using E85 either....




that 15-20% less use of E85 due to the more aggressive cam tuning renders the E85 to be roughly what 1.2-1.25 gallons of E85 to 1 gallon of gas for the same distance?

[s2d4]

HINT:
Tuning for more power is completely different to tuning for MPG.

[cdrazic93]

Originally Posted by s2d4

HINT:
Tuning for more power is completely different to tuning for MPG.

That's what I was trying to get at, but evidently failed at explaining. E85 is for making power not worrying about MPG's. Gas is for daily driving.

[reeves]

Originally Posted by cdrazic93

E85 is for making power not worrying about MPG's. Gas is for daily driving.

It's not anything to worry about.. but if I can have my E85 cake and eat it too, why not?

[steve99]

Originally Posted by mad_sb

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.

This may be considered "dodgy" but couldn't you deliberatly offset the O2 scaling to "trick" the ECU into thinking it was running 14.7 when in fact was running leaner.

As long as it was a constant offset you could adjust the OL fuel table to compensate.

The OFT E85 tunes do a similar trick with injector scaling .

[Element Tuning]

I did experiment once to fully maximizing my Hydra EMS on my Legacy GT while using E85. The goal was the same power, so I ran the same boost level but maxized fueling, ignition timing, and variable can timing. I was able to get in the 10-15% range of gas fuel economy which was important as it made E85 about the same cost as fuel in terms of mileage.

Now E85 has a huge working range and I was able to run 17:1 in some areas and under full load I could run 13.5 AFR vs never leaner than 14.7 and 10.8 under load (stock TMIC).

Now using the Hydra EMS on my FRS I'm seeing different fuel volume requirements because of the direct injection and how it increases the power potential of E85 even more than on a port injection only engine. Now I can run similar AFR ranges but I'm having to increase fueling I'm the +47% range at maximum power over pump fuel. Also I'm finding the FA20 motor does not want to run as rich on E85 to make maximum power like I see with our EJ race engines. On those engines we'll rich misfire before we peak out on power.

Thanks,
Phil Grabow