mixing e85 (109 octane) with e15 (91 octane)

[shr133]

Originally Posted by pcguru2000

Being so close to e85 stations, I was thinking about doing an experiment to save a tiny bit of money and at the same time get a little more power.

I don't have a flex fuel kit but in other forums, someone said that the ecu could slowly adjust to e85 without any issues. This car is also a daily driver and I would't have an issue with the ethanol separating because it's sitting there an extended time.

I saw this chart which someone created with different mixes of e85.

I'm putting 5 gallons of e85 and 5 gallons of e15 91 octane. According to the chart, that would be 100 octane. Since the ecu can slowly learn to take a full tank of e85, wouldn't learn a little faster (since it's not so extreme) to only have a 50% tank of e85 mixed with regular 91 gas? Even if the e85 gas I put in is only e50. Wouldn't that be easier for the ecu to adjust than going from e85 to e15?

After running my flex fuel kit this year you could get away with a gallon or 2 of E85 per tank but the tune would be off so don't know if you see any gains unless it's really hot out. but for 5 gallons you would need a tune or flex fuel kit. And after the first tank you would loose track of your ratio. Plus the gas doesn't mix perfect I've seen my mix change from E25 to E40 on the same tank so it takes some driving to mix everything together.

Bottom line for E85 to help it needs to be tuned and the easiest way is with a flex fuel kit..

[shr133]

But if money is a problem it's safer to go to E85 and flash in a new map after it works it's way through the system, the problem is if you ever go back the other way the extra timing can break things, so you have to be careful.

If you are building your own maps bump up knock correction to pull more timing faster ( I bump this up anyway using pump gas) and don't get crazy with the timing. When you data log make sure to back timing down so there is no knock correction + a little(.5) to be safe with 91 or 93..

So build a really good base map than go to E85...

[ItsReiko]

Originally Posted by steve99

The ECU will only cope with adding about 10-15% ethanol in petrol when your on petrol tune.


just be aware that a lot of fuels already have 10% ethanol added.



ie dont add more than about 6 litres of E85 to your full tank of petrol (straight petrol no ethanol already added) on a petrol tune,




same for an dedicated E85 tune your ok with about 10% or so variation, the E85 tunes are usually done on about E70 so your ok with 60-80% or so before fueling get too far off.


outside that you need flex kit or different maps


talking NA motors, boosted you need flex kit to run E85 unless you have a known consistent source of E85, which does seem to be case in USA

Sorry for reviving such an old post, but does that mean if my e85 station supplies consistent minimum e83-e87, then I'm actually not really optimized for the OFT v4.03 e85 tune and would benefit from mixing in like 1 gallon of 91 gasoline?

[Lantanafrs2]

Originally Posted by ItsReiko

Sorry for reviving such an old post, but does that mean if my e85 station supplies consistent minimum e83-e87, then I'm actually not really optimized for the OFT v4.03 e85 tune and would benefit from mixing in like 1 gallon of 91 gasoline?

Don't mess with it.

[Qwimby1]

FWIW, the OBDLink MX monitor can display alcohol fuel percentage. I used to use mine all the time for oil temp, but I can't get oil pressure with it so, I'm going to a dual gauge.

[steve99]

Originally Posted by ItsReiko

Sorry for reviving such an old post, but does that mean if my e85 station supplies consistent minimum e83-e87, then I'm actually not really optimized for the OFT v4.03 e85 tune and would benefit from mixing in like 1 gallon of 91 gasoline?

The oft e85 tunes are set for about 75% ethanol so they wll cope with about 60-90% ethanol range

NA car no real advantage past about E70