Blending in E85 with 91 octane

[Paul_G]

We can only get 91 octane around here. I have my old cars tuned to run on it. But, can blending in a little E85 in the fuel tank help increase the octane, and with a little more timing increase the power?

So I started thinking, I know the carb, or even the aftermarket EFI in my 73 can not run straight E85. Too corrosive. But they are running on E10. So what if I blended in 3 gallons of E85 with 15 gallons of 91? For an 18 gallon tank that would only be about 15% E85.

My simple calculations, 3 gals of E85 with 15 gals of E10 would make the 18 gallon tank E23.

Would that be enough of an octane boost to be worth while?

 

[Photon440]

It would run leaner, if nothing else. You need more fuel with more alcohol.

 

[Kern Dog]

True. The E85 needs approximately 40% more fuel flow to produce the same energy. Blending is a step backward.

 

[Paul_G]

I am going to try this in the 73 with EFI. Yes, the engine will consume more fuel. My question is if the EFI/injectors will add the additional fuel automatically to maintain the AFR setting, or will I have to change the AFR richer to get the fuel?

 

[451Mopar]

The EFI should be able to compensate if the pump and injectors can deliver the additional fuel flow.
On the '69 Coronet with FAST 2.0 EFI, I have a flex fuel sensor in the fuel line to determine the alcohol content of the fuel.

 

[PRHeads]

With more alcohol the mixture should be made richer.
If the EFI is targeting, let’s say 13.5:1, and the correct mixture for the new higher alcohol blend is 1 point richer...... if you don’t reprogram for that, how does the EFI know it’s supposed to be richer?

The cars that have Flex Fuel capability have a means of determining the alcohol content in the fuel, and the timing and fuel maps are adjusted accordingly.

How does that happen with a typical Sniper type system?

 

[Paul_G]

With more alcohol the mixture should be made richer.
If the EFI is targeting, let’s say 13.5:1, and the correct mixture for the new higher alcohol blend is 1 point richer...... if you don’t reprogram for that, how does the EFI know it’s supposed to be richer?

The cars that have Flex Fuel capability have a means of determining the alcohol content in the fuel, and the timing and fuel maps are adjusted accordingly.

How does that happen with a typical Sniper type system?

That has been proven this morning. I put in the 3 gals of E85 and topped off the tank with 91. I dont yet have a way of knowing how much ethanol is actually in either blend, or what it actually is in my tank. The allowed Ethanol tolerance in the fuel is very wide, so I have read.

So, after a few minutes of driving the engine started to run a little rough, felt like a lean surge coming on. Richened up the idle, cruise, WOT, 0.5 point each. Engine smoothed back out. So far I would say my experiment with E85 is working. Calculated out it should be E23, but without a meter in the fuel line reading the alcohol content I can only assume what it is.

This is what's great about EFI. I would not even try this with a carb. It took literally seconds at a stop light to change the AFR's.

My reason for doing this, I can not tell if there is spark knock at full throttle, or just the noisy valve train talking to me. It is a full roller motor.

 

[Slap Stick]

Problem with high ethanol content is as stated it is corrosive. Plus the rubber bits in the fuel system don't like it. You need higher compression to take advantage of the ethanol. Spark plugs are harder to read and in cooler weather engines get harder to start. And with the richer mixture you run the possibility of washing the cylinders with the stuff, contaminating the oil.
When I was helping my late friend with his dirt cars we ran E100. Had to run almost 3x the fuel as race gas to make the same power. Ran cool, though. Even on hot TX nights we sometimes had to block off part of the radiator.
Compression was 14:1.
And the oil tank filled with ethanol from blowby.

 

[451Mopar]

I think with the simpler EFI systems without flex-fuel sensor, just need to save off different tunes. That's one nice thing with EFI, just load a new tune for different fuel.

 

[Paul_G]

I think with the simpler EFI systems without flex-fuel sensor, just need to save off different tunes. That's one nice thing with EFI, just load a new tune for different fuel.

Exactly. I already saved the tune before the E85 was added to the fuel. I can adjust the tune now to dial in the flex fuel settings. When this tank of fuel is gone, easy peasy to go back the 91 octane tune. It would be even better if the ECM was controlling timing. My system is not doing that... yet.

 

[dvw]

We run the E85. No big deal. At the eed of the year it gets gas run thru it. Beginning of the year we go thru the carb and clean it for another season. Aluminum fuel cell no issues. Use PTFE hose. Set it and forget it.
Doug

 

[RJRENTON]

We can only get 91 octane around here. I have my old cars tuned to run on it. But, can blending in a little E85 in the fuel tank help increase the octane, and with a little more timing increase the power?

So I started thinking, I know the carb, or even the aftermarket EFI in my 73 can not run straight E85. Too corrosive. But they are running on E10. So what if I blended in 3 gallons of E85 with 15 gallons of 91? For an 18 gallon tank that would only be about 15% E85.

My simple calculations, 3 gals of E85 with 15 gals of E10 would make the 18 gallon tank E23.

Would that be enough of an octane boost to be worth while?

I believe it's not a strict volumetric calculations but a calc based on the heating value (energy) in terms of BTU/GALLON (or some other unit of measurment) of the heating values of the fuel that is being blended. As you know (or not) the BTU content of Ethanol is half that of gasoline. For example, if gasoline is 140,000 Btu/gallon, and ethanol is 70,000 Btu/gal and to achieve the same energy equilivant, nominally twice the amount of ethanol is required. The newer vehicles have the ability to analyze the incoming fuel mix (density) prior to injection, and adjust the injector's on time (pulse width modulated), to allow more of the mix, based on the energy value, to produce the same level of power.
It is likely that your supposition will result in lower heating value of fuel being combusted. But, perhaps you should try your blend as an experiment, reporting faster elapsed time or better/less MPG or more or less power produced. The EFI boys have a definitive advantage over us carburetor people in that they can adjust the fuel injector delivery curve and trim with real time down stream oxygen analysis. Just my opinion of course.
BOB RENTON

 

[Paul_G]

I believe it's not a strict volumetric calculations but a calc based on the heating value (energy) in terms of BTU/GALLON (or some other unit of measurment) of the heating values of the fuel that is being blended. As you know (or not) the BTU content of Ethanol is half that of gasoline. For example, if gasoline is 140,000 Btu/gallon, and ethanol is 70,000 Btu/gal and to achieve the same energy equilivant, nominally twice the amount of ethanol is required. The newer vehicles have the ability to analyze the incoming fuel mix (density) prior to injection, and adjust the injector's on time (pulse width modulated), to allow more of the mix, based on the energy value, to produce the same level of power.
It is likely that your supposition will result in lower heating value of fuel being combusted. But, perhaps you should try your blend as an experiment, reporting faster elapsed time or better/less MPG or more or less power produced. The EFI boys have a definitive advantage over us carburetor people in that they can adjust the fuel injector delivery curve and trim with real time down stream oxygen analysis. Just my opinion of course.
BOB RENTON

The EFI I am using, an old Edelbrock E Street system I bought used, is not E85 compatible. My experiment is to use E85 trying to increase the octane level above the 91 I can get at the pump around here. I have not found any calculators online that can estimate octane level when blending E85 with other grades of fuel. If you know of any please pass it along.

I know that the Feds are considering raising the Ethanol levels we get at the pump to 20% from the 10% they allow now. If that happens we all may be using something similar to whats in my fuel tank right now. And I can say that the high compression old school big block engine did not like it. Until I changed the AFR to a richer mix.

In my simple mind the blended fuel in my tank should be higher than pump 91. Simple math, 15 gallons of 91 octane= 1365, 3 gallons of 108=324, 1365+324= 1689, divide that by 18 and we get 93.8. So simple math says 93.8 octane.

Is a 2 to 3 point bump in octane enough to show a performance gain?

Can my fuel delivery system and the EFI injectors supply the larger required amount of the E23 blend?

 

[RJRENTON]

The EFI I am using, an old Edelbrock E Street system I bought used, is not E85 compatible. My experiment is to use E85 trying to increase the octane level above the 91 I can get at the pump around here. I have not found any calculators online that can estimate octane level when blending E85 with other grades of fuel. If you know of any please pass it along.

I know that the Feds are considering raising the Ethanol levels we get at the pump to 20% from the 10% they allow now. If that happens we all may be using something similar to whats in my fuel tank right now. And I can say that the high compression old school big block engine did not like it. Until I changed the AFR to a richer mix.

In my simple mind the blended fuel in my tank should be higher than pump 91. Simple math, 15 gallons of 91 octane= 1365, 3 gallons of 108=324, 1365+324= 1689, divide that by 18 and we get 93.8. So simple math says 93.8 octane.

Is a 2 to 3 point bump in octane enough to show a performance gain?

Can my fuel delivery system and the EFI injectors supply the larger required amount of the E23 blend?

Try this link to a canned program....it may offer some insight to your question.

http://www.csgnetwork.com/octanemixcalc.html

There are several other sources as well....
BOB RENTON

 

[451Mopar]

Link to FastMans document for flex-fuel setup for the FAST 2.0

https://702f0520-6ff9-41eb-a3d9-d9b...84956ca206b3ef48.doc?dn=EFI and Flex Fuel.doc

 

[Paul_G]

Link to FastMans document for flex-fuel setup for the FAST 2.0

https://702f0520-6ff9-41eb-a3d9-d9b60e0d6a4a.filesusr.com/ugd/82c417_e9c76b3ce390412e84956ca206b3ef48.doc?dn=EFI and Flex Fuel.doc

In the chart it states Gasoline has a 14.7:1 stoichiometric rating, which we use when tuning gasoline engines. It also states that E85 is Stoich at 10.0:1.

We do not have 100% gasoline anymore. It is all cut with ethanol. So the stoich number is going to be lower than 14.7. Something to consider.

 

[451Mopar]

You could use lambda and not the A/F Ratio. Not sure if the Sniper does that?
http://blog.innovatemotorsports.com/lambda-vs-afr-whats-the-difference/

 

[Paul_G]

Very informative read. Thank you.