Re: plug reading when running alcohol

Alex Degnes /
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I'm starting to get really excited about this fuel, promising results so far.

Some propaganda for the non-believers:

About turboed cars, but much of the same aplies to a piped two stroke.

"Since i have not seen any real concrete info on E85 Air/Fuel ratios on this forum, i figured i would throw up what i know so that some of you can make more educated decisions on what AFR you should tune for on E85. I will only discuss E85 AFRs in this thread and will start a thread regarding ignition timing in the near future, as i don't have the time to do it currently.

I have been tuning many years and have a lot of experience tuning all of the exotic race fuels, along with pump gas. This was actually my first attempt at tuning E85(due to just getting it in my area), but before i attempted to tune the "Corn Juice" i did a TON of research on this amazing alternative fuel. Some things about E85 i already knew, but i found there was a lot i didn't. I want to share what i have learned while tuning my own car on E85.

Despite E85 having been around for a several years now, there is still a vacuum of info on the fuel and some of the info i found was completely incorrect. Most of your pro tuners out there know that E85 is probably one of the best fuels on the market at any price, but they aren't so quick to give up what they know on the subject.

First we're gonna start off with Air/Fuel Ratios and what they mean with reference to E85.

E85 has a stoichiometric fuel mixture of roughly 9.78-9.8:1 in E85's purest form (Class 1 85% Ethanol summer blend). As the fuel's Ethanol content goes up the stoich range goes down. For instance, 100% Ethanol's stoich is about 9.0:1.

E85 will maintain max brake torque much richer than stoich than gasoline will. But, because of it's excellent detonation threshold(due to lower combustion temps, lower peak cylinder pressures..etc), it can be run much closer to stoich than gasoline safer. E85 reaches max thermal efficiency at about 13% richer than stoich, whereas gasoline is about 16% richer than stoich(with pump gas being even richer). But again, E85 can maintain Max Brake Torque well into the 30% richer than stoich range, unlike gasoline which is limited to about 18% rich of stoich. DISCLAIMER: Just because E85 itself will still make power at super rich AFRs, doesn't mean it's a good idea or even recommened. A whole host of issues come with running super rich AFRs, that you need to be aware of, but i will cover later.

Therefore Max Rich Torque of E85 is 7.1:1- 8.5:1

With that being said, here is what i would consider a very safe and conservative fuel tune on E85. *AFR's listed in bold are for widebands o2s that are calibrated for gasoline, AFR's in ( ) are actual E85 AFR:

Part Throttle lean (max eco) AFR of 16.5:1(11.0:1) 12.4% leaner than STOICH

Part Throttle rich AFR of 14.7:1(9.8:1)

Spool up... AFR of 13.5:1(9.00:1)

WOT... AFR of 12.1:1(8.06:1) 17.7% richer than STOICH

*If you're using a wideband that is calibrated for gasoline(14.7:1) and cannot change the calibration of the wideband, take your gasoline AFR and divide it by 1.5 to get actual e85 AFR or use the wideband in lambda mode. 1 lambda is 9.8:1

Here are some common AFR conversions(Gas AFR on left, e85 on right):
















Of course, all engines are different and there is still a lot of trial and error when tuning any setup. Having the ability to measure torque output is a must for tuning both fuel and ignition timing with E85. We are only talking about E85's fuel properties in this thread and not taking into consideration ignition timing, boost pressures, different E85 fuel mixtures..etc. Care must be taken when combining all the aspects of the tune and setup, to assure proper limits and safety.

Now that we have that out of the way, let's compare E85 with pump 93 octane.

As you can see, the lean side of max rich torque for E85 is 8.5:1, which is 13% rich of stoich. We know gasoline's max rich torque is about 12.5-13.0:1, but because of pump gas' low detonation threshold, we must run AFR's much richer with forced induction. Therefore, AFR's of 22+% rich of stoich must be used to combat detonation, while running E85 13-15% rich of stoich results in no detonation. Why is this, you ask?

Here are the reasons why:

1. Lower EGT's. E85 will typically see EGT's 200c below pump gas at the same relative AFR (for instance 12.5:1 pump, 8.33:1 E85)

2. Octane rating of 105 with class 1 e85(raises detonation threshold)

3. Very high vaporization cooling, much more than gasoline, which lowers mixture temps, thus increasing detonation threshold, along with increasing VE

4. Peak cylinder pressure are lower while maintaining a higher and longer overall cylinder pressure, thus raising detonation threshold and making more power due to increase in crank angle

5. E85 burns much more efficiently than gasoline, 27% more efficient

6. despite lower EGT's, E85 creates more exhaust gas volume, which helps with spool without added EGTs

So, we know that E85 has a very high detonation resistance, one thing E85 does not have much tolerance for, is pre-ignition. This is where E85 starts to wander from exotic race fuels. E85 cannot withstand pre-ignition as well as it can detonation. I believe this is due to the fact that it actually burns much faster than gasoline(pump or race fuels), among other things. While it's very tolerant to lean mixtures(detonation), over-advanced ignition timing takes a toll quickly on E85. While E85 will take more ignition timing than pump gas overall, it will not allow a lot of ignition advance at peak VE, but will want more and more advance as RPMs rise, this ending up with much higher peak timing numbers. We'll get into that in the timing thread i will start."

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