What are you guys using for stoich for e85?
I have seen numbers from 9.76-9.85
What are you guys using for stoich for e85?
I have seen numbers from 9.76-9.85
9.765
My local station is fanTAStic. It's 85% already/still and all the other ones I've tested are 70 ish.
9.85
What is the reasoning behind this? Can you elaborate on why people are using different stoich points.Originally Posted by wbt
To compensate for fluctuations in ethanol content I think and keep the short trims down.
That'd be my reason
But if say my local station has never been under 85% ethanol and sometimes slightly higher, by using 9.85 I would then be targeting a leaner than stoich mixture?
Less fuel used per air mass; sure. But this is how I process it:
If you're maf table is perfect (let's say trims are always 0%)
You're tuned at that 0% on a fuel that's stoich of 9.765.
You put in fuel that's say 10.0 (it's e70 or whatever).
Trims are going to be negative if you do not tell the vehicle the stoich is changed.
The pcm only cares about lambda and not actual afr. It's always looking for stoich of 1.0 no matter what fuel is in it. It's going to take your perfectly 0% maf table and start pulling negative trims to get back to 1.0
Strictly made up numbers:
Let's say it takes 1ms of pulsewidth to hit 1.0 on 9.765 stoich fuel
It'll take less (maybe .9ms) of pulsewidth to hit the same 1.0 on a 10.0 stoich fuel.
Th mixture isn't leaner when you use the lambda scale; which is what the pcm looks at. The amount of fuel to get that stoich 1.0 was less though.
If you're tuning a customer it's better to give a little wiggle too since you don't want trims to be out to lunch. If you're at 0% on say 10.0 fuel the pcm has to trim less out if you get higher or lower content ethanol.
That all said; dial the maf on a fuel you know the stoich for, then enable ffv and it'll do it on its own, it'll figure out the calculated stoich and thus ethanol content. That's what I have mine doing. It's only ever filled with e85 but I still have ffv on.
Depending on where you get e85 locally you may get e70 or e90. Most of the ethanol stuff I work with has easy access to lower ethanol content fuel.
For race fuels like MS109 or C85 I use the manufactures provided stoich values. C85 = 9.66.
Last edited by wbt; 03-11-2017 at 12:36 AM.
Different areas have different blends for sure. We use a 10.0 stoich here. Luckily octane rating is fairly steady at anything E60ish and above. God bless flex fuel logic.
Here's what I do:
Use ethanol tester to determine exact ratio of ethanol to gas.
If I have exact e85, I calculate:
.85 x 9(stoich of 100% ethanol)= 7.65
.15 x 14.7(stoich of 100% gas)= 2.21
7.65 + 2.21 = 9.86
My last batch tested at 87% ethanol, so my stoich is 9.74.
Must be nice. Locally I'm testing around 65ish% ethanol in the cold on my daily. I'm being told its common to see 80 to 90% in the midwest around the time for hot rod drag week.
Well, there's good and bad. The good is being in TX we don't really have much of a winter blend, but the bad is it's not widely available and I have to drive 3 hours to fill my 2 drums.
Valero has a lower % blend in cooler months in Austin. Best I have seen is 85% with them in warmer months.Well, there's good and bad. The good is being in TX we don't really have much of a winter blend, but the bad is it's not widely available and I have to drive 3 hours to fill my 2 drums.
HEB tests 90% year round.
Yep, HEB of Parmer and the one Near Cabelas are always e87ish...Valero seems to be e70 almost year round...
I'm in the Tyler/Longview area now and the closest stations are Dallas/Shreveport, but I filled my drums in Houston because I know the Stripes/Sunoco stations have a rep for good e85. Plus, my daughter lives in the area so it wasn't a trip just to get fuel. If anyone has any info on how e85 tests in Dallas/Shreveport, please share.
What WOT Lambda are you using for max power with E85?
I also noticed that Ford uses a Stoich of 10.26 for their Flex Fuel Vehicles.
Ive seen ranges from 820 to 855.
The testing we did showed more power with a richer mixture.
I usually have WOT Lambda set to .83 and Flex Fuel WOT lambda set to .85
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