Any reason we can't blend in some e85 for knock resistance?

[KrisR]

I was thinking about this the other day. I have a 93 octane tune that I haven't used yet because I have not been impressed with the BP 93 gas that is sold in my area. I got quite a bit of KR even on my 91 tune using this fuel. I was thinking about adding some 100 unleaded for track days / weekend playing but then I thought about splashing in a few gallons of e85.

Our cars are always in closed loop, fuel trims are always maintaining commanded air/fuel ratio. As long as we keep fuel trims in a reasonable range, why couldn't I run some e85 in the tank to raise octane?

I figure even running 1/4 tank of it (4 gallons of E85, 12 gallons of 92 pump gas) should still keep fuel trims under 10%, which should be no problem. I have run E85 in my previous two F/I Mustangs so I know the upsides and downsides.

4 gallons of E85 and 12 gallons of 92 should produce around 95 octane and a cooler burn, and should change fuel trims around 8% by my calcs.

Not like we need to worry about running out of fuel system in our cars with a couple bolt-ons.

 

[86GT351]

I was thinking about this the other day. I have a 93 octane tune that I haven't used yet because I have not been impressed with the BP 93 gas that is sold in my area. I got quite a bit of KR even on my 91 tune using this fuel. I was thinking about adding some 100 unleaded for track days / weekend playing but then I thought about splashing in a few gallons of e85.

Our cars are always in closed loop, fuel trims are always maintaining commanded air/fuel ratio. As long as we keep fuel trims in a reasonable range, why couldn't I run some e85 in the tank to raise octane?

I figure even running 1/4 tank of it (4 gallons of E85, 12 gallons of 92 pump gas) should still keep fuel trims under 10%, which should be no problem. I have run E85 in my previous two F/I Mustangs so I know the upsides and downsides.

4 gallons of E85 and 12 gallons of 92 should produce around 95 octane and a cooler burn, and should change fuel trims around 8% by my calcs.

Not like we need to worry about running out of fuel system in our cars with a couple bolt-ons.

That is a great question. Maybe you can ask Ken at LUnd that question as he tunes alot of E85 ars here in South Florida!

 

[cbrtrx]

I have already tried this. Keep the blend around 80 percent gas to 20 percent ethanol and the trims will be very close, the car will tolorate about 2* of timing with that ratio.

 

[PNR Welding]

Your gonna change the stoich in the tune for it to be right.
Plus most gas is 10% ethanol.

 

[KrisR]

Your gonna change the stoich in the tune for it to be right.

If I want to zero out the fuel trims, yes. If I can deal with a few percent in the LT/STFT, I don't think so.

Plus most gas is 10% ethanol.

Yes it is. That means even less fuel trim change.

 

[beefcake]

well, stoich of e85 is way different than fuel, you will run leaner if you don't change the stoich in the tune

 

[stkjock]

I would thi k to get the most out of the fuel mix, you would want it tuned properly, my $.02

 

[KrisR]

well, stoich of e85 is way different than fuel, you will run leaner if you don't change the stoich in the tune

Don't the factory 02s just work off lambda? Don't you tune for the same lambda (e.g. 0.84 at WOT) on E85? Won't it try to maintain the same lambda no matter what fuel is in it?

So what you are suggesting is that if I (for example) just replaced my tank of gasoline with e85 and didn't change the tune, there would be no codes thrown due to running lean, the fuel trims wouldn't change, but the car would be running ~30% leaner? I disagree, I think that the fuel trims would come in to play and the computer will begin adding long term fueling if I don't go crazy with the amount of E85. Obviously I would not just run a full tank of corn because I'm sure that 30% is way too much for the fuel trims to account for.

I would thi k to get the most out of the fuel mix, you would want it tuned properly, my $.02

Yes, of course an E85 tune would be the best/only solution if I was running 100% E85.

 

[05yellowgt]

12 gallons of e10 and 4 gallons of e85 would give you a stoich going from 14.076 down to 13.01, or over a full point. I would NOT run that big of a change of fuel without adjusting the tune to compensate. I would at least change the stoich setting in the tune so it can intelligently do its thing without base parameters being off.

 

[stkjock]

Yes, of course an E85 tune would be the best/only solution if I was running 100% E85.

I said mixture, as in as you propose mixing it, not a pure E85 tune.

 

[KrisR]

12 gallons of e10 and 4 gallons of e85 would give you a stoich going from 14.076 down to 13.01, or over a full point. I would NOT run that big of a change of fuel without adjusting the tune to compensate. I would at least change the stoich setting in the tune so it can intelligently do its thing without base parameters being off.

Yep, an 8% change, like I said. Well within the parameters of the fuel trims on these smart Coyote processors, no? Are they only good for very very very small adjustments or what? I've seen way more that on a couple old tunes in previous cars (for small amounts of time).

 

[BruceH]

Lambda is lambda no matter what the fuel. Most people run the same lambda for their e85 and gasoline tunes.

You should try it and see what happens. I know that the srt4 and Subaru people add e85 to their tanks for just this reason. If you have a blender pump available just pump in e30 and go.

The big question is what is the allowed error in fuel trims before a code it thrown? If you had the software you could just change where the error comes on (I have mine at 1.4 to .6 just in case I get stuck somewhere with limited fuel options) and it should be good.

Someone has to try it, might as well be you op, lol. Send a pm to Seer about how much trim is allowed. He has the tuning software and will be able to look at the stock parameters.

 

[CPRsm]

Lambda is lambda no matter what the fuel. Most people run the same lambda for their e85 and gasoline tunes.

It's not that easy in the tune. The pulse width is going to change because of the stoich target and if you don't calulate for it other calculations down the line will be wrong, like load and timing tables because the estimated lb/min was off. I wouldn't let it just correct personally. Corrections are reactionary like knock sensors. Wibebands are showing how much it's off and the correction. But until the ltft are learned it won't be right. Then you throw gas in and it's wrong all over again lol.

 

[KrisR]

Thank you for the input so far, all. If it won't work, fine. I know how bad detonation is for any hyper-piston engine and I thought this would be the perfect car to try it on (it self-adjusts! LOL).

 

[05yellowgt]

Get your tuner to make a tune with the stoich adjusted try it out and datalog to see where you are. What you want to do willwork, just ago about it in a smart and proper way.

Sent from my Transformer Prime TF201 using Tapatalk HD

 

[KrisR]

Get your tuner to make a tune with the stoich adjusted try it out and datalog to see where you are. What you want to do willwork, just ago about it in a smart and proper way.

Sent from my Transformer Prime TF201 using Tapatalk HD

Well if I had a tuner I would just have him write me an e85 tune and run it 100% but that's not the point. Nevermind.

If I have to I might spring for an AED or Lund E85 tune. Currently have Bama tunes and they don't offer anything corn related.

 

[BruceH]

Your stoich would change from 14.1 to 13.5 going from e10 to e20. A difference of about 4.4%. That's well within the parameters of what the stft and ltft can correct for.

I don't really see the harm but it's not my car and not my risk. Plenty of people run e10 with a gasoline tune. Gas is 14.64 and e10 is 14.1, a difference of about 3.9%.

I would view running e20 on an e10 tune no different than running e10 on a gasoline tune but that's me.

 

[cbrtrx]

▲▲▲ Correct like I said I've done it already, with an E20 blend trims changed less then 4 percent which is well within aceptable ranges to make no tune adjustment fuel wise. Anything more then E20 blend then I would change stoich.

 

[KrisR]

▲▲▲ Correct like I said I've done it already, with an E20 blend trims changed less then 4 percent which is well within aceptable ranges to make no tune adjustment fuel wise. Anything more then E20 blend then I would change stoich.

What benefits did you see with this? Did you see less KR like I would think you would, did the car feel better, etc?

 

[wiplash]

Kris, I'll do this after I get some data logging in on the Bama 93 race tune and Casey's tune for comparison. We both know the Bama tune is more aggressive on the timing so that should tell the tale.

I did this for years on my TBSS with success.