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2G Built motor and flex fuel

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gst-turbo

Proven Member
677
58
Nov 7, 2012
Petaluma, California
Got my motor being built at the machine shop and have e-85 high compression piston on it 10.5. Will I be able to run flex fuel on it for daily driving? If I do daily drive it will be on a mix of e-85 and 91 and probably won’t be getting on it just a small 10 minutes drive to work. My c6 z06 corvette is always on e-85 and some time flex fuel haven’t had a problem running out of e-85 I usually have three barrels at home full. But on rare occasion I do want to drive it a few he away from home with no e-85 stations will this be possible?
 
You would need a way for the ecu to compensate for the Ethanol vs Gasoline, it would need a flex fuel sensor and the work done to the coding in order for the ecu to understand which fuel and ignition maps to reference, that also means having two tuned fuel maps and two tuned ignition maps, if you wanted to run just Ethanol all the time that would simplify things a good bit and you could run it fine on that compression ratio, you would need the right size injectors, a fuel pump that can keep up, fuel lines that can handle Ethanol, a fuel pressure regulator thats adjustable that can handle Ethanol, a fuel filter thats Ethanol compatible and then the ecu needs set up for it and you should be good to go.
 
I am very familiar how e-85 works just not on a high compression motor and not on ecmlink. On my corvette it’s heads cam intake and full bolt ons I have a flex sensor that just reads the % of the mix on hptuners and adjust depending on the mix I can run 100% gas if I want with no adjustments needed makes a little over 600hp. Well 99% of the time it’s on e-85. I have owned a dsm since I was 16 so about 9 years but never on a high compressor motor or on e-85. Dose ecmlink have the ability to adjust on the fly like hptuners dose? Or do I need to just run e-85 all the time and if I run out of e-85 it’s pretty much over? I don’t mind running e-85 all the time just sometimes I want to take a trip I do live in California were there’s bearly any e-85 station around the closed being about 1hr away but I fill up three barrels ever 4 months for the corvette not my daily just a weekend car/drag car. My 2020 bmw s1000rr is about to be on e-85 also so I will be needing a few more barrels to bring home
 
Yes, I have a GM flex fuel sensor in my car (with ecmlink) and it takes care of fuelling on the fly. You can pretty much forget about it after you set it up.

It requires speed density to free up the extra input for the ECU.

The only issue is timing. I think most people set the maxoct table to whatever they want to run on e85, and set the minoct table to the gas tune's maxoct, so if it knocks then it isn't able to pull a ton of timing like the stock map will. I left the minoct table alone on my car, so that it can pull a ton of timing if it needs to. Of course this means the timing is going to be retarded a lot if I put regular gas in the tank. My car has e85 full time so it has not been an issue.
 
Yes, I have a GM flex fuel sensor in my car (with ecmlink) and it takes care of fuelling on the fly. You can pretty much forget about it after you set it up.

It requires speed density to free up the extra input for the ECU.

The only issue is timing. I think most people set the maxoct table to whatever they want to run on e85, and set the minoct table to the gas tune's maxoct, so if it knocks then it isn't able to pull a ton of timing like the stock map will. I left the minoct table alone on my car, so that it can pull a ton of timing if it needs to. Of course this means the timing is going to be retarded a lot if I put regular gas in the tank. My car has e85 full time so it has not been an issue.

Tune it conservatively on pump first then move the two tables, afr and timing tables to minoct. Then tune e and leave both as the maxoct. Why wouldn’t it pull timing when it needs to?
 
I would stay around 9.0:1 compression since 10.5:1 is walking a tightrope on 91 octane. Get your E85 power from added boost and timing. The point of Flex Fuel is to have the car perform well on both fuels - the car won't perform well on 91 since it will be seriously boost limited. If you stick with 10.5:1, just keep in mind that the 91 octane map will largely just be used to drive around, not really to go fast.
 
Tune it conservatively on pump first then move the two tables, afr and timing tables to minoct. Then tune e and leave both as the maxoct. Why wouldn’t it pull timing when it needs to?

Maybe I misunderstand, but isn't the minoct table the farthest it can retard the timing? So say you get a bad batch of fuel or its really hot out and it wants to ping, your timing is basically locked at the minoct value because it's interpolating off your ethanol content sensor, it no longer has the ability to pull timing past that, down to the crazy low stock minoct table.

Correct?
 
Maybe I misunderstand, but isn't the minoct table the farthest it can retard the timing? So say you get a bad batch of fuel or its really hot out and it wants to ping, your timing is basically locked at the minoct value because it's interpolating off your ethanol content sensor, it no longer has the ability to pull timing past that, down to the crazy low stock minoct table.

Correct?

Under Aux Maps, you can set the %ethanol to run the minoct table. Once it’s at or below that %, it will run off the minoct table. If it picks up knock, it will pull timing accordingly.
 
I didn't realize it could pull timing down past the minoct table

So theoretically I can paste my old gas timing table into minoct and not worry about it being able to pull timing? What is the purpose of the minoct table then?
 
I didn't realize it could pull timing down past the minoct table

So theoretically I can paste my old gas timing table into minoct and not worry about it being able to pull timing? What is the purpose of the minoct table then?
Yes. I run 10:1 on mostly E85 but she still gets 91 sometimes and the flex fuel setup will take care of it all. If your knock sensor is set up and working then it will pull timing accordingly. Mine doesn't run like it can on 91 and is SERIOUSLY limited on timing, 4 or 5* MAX for gas. On E, it will let me run 15* easily.
 
I didn't realize it could pull timing down past the minoct table

So theoretically I can paste my old gas timing table into minoct and not worry about it being able to pull timing? What is the purpose of the minoct table then?

I don’t see why it wouldn’t. I’ve read links wiki page several time and it doesn’t mention anything about that which I think would be very important bit of info.
 
Awesome, ill have to do that. I haven't blended my fuels yet, but if I had to switch back I was going to paste my gas timing table back in maxoct and back the boost off.

I guess all I need to worry about is dialing back the boost.
 
Awesome, ill have to do that. I haven't blended my fuels yet, but if I had to switch back I was going to paste my gas timing table back in maxoct and back the boost off.

I guess all I need to worry about is dialing back the boost.

That’s the only thing I worry about too. I’m not sure if link has the function to do that when using ebc through link. Haven’t gotten that far yet LOL
 
https://www.ecmtuning.com/wiki/longtermoctane

It looks like the minoct is the lowest timing it will go.

I haven’t read this one. Thanks for sharing.

I don’t see where it states that the minoct is the lowest it will go.

This adjustment is done by monitoring knock retard (the amount of ignition delay added in by the ECU in response to knock sensor activity). More detonation means more knock retard and a lower “value” for the ECU's fuel octane rating.
 
Lower down it says it:
"LTOctane has a scale of 0 to 255. A value of 0 means use the timing value retrieved from the “bad octane” table. A value of 255 means use the timing value retrieved from the “good octane” table. Values in between result in interpolation between these two extremes. At 128, for example, the timing value used will be the mid point between the “good” and “bad” octane table values."
 
Lower down it says it:
"LTOctane has a scale of 0 to 255. A value of 0 means use the timing value retrieved from the “bad octane” table. A value of 255 means use the timing value retrieved from the “good octane” table. Values in between result in interpolation between these two extremes. At 128, for example, the timing value used will be the mid point between the “good” and “bad” octane table values."

That just says it interpolates between the two depending on what value it reads for fuel. I still think it's unclear.

What happens when you set both min and max tables the same, and then it picks up knock. It won't pull any timing? This test would clear thing up imo
 
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I've done that Tony, mine still pulled timing as normal. It was back when I was learning to tune and I had both maps identical.
 
That just says it interpolates between the two depending on what value it reads for fuel. I still think it's unclear.

What happens when you set both min and max tables the same, and then it picks up knock. It won't pull any timing? This test would clear thing up imo
I don't know for certain but this sentence (we've both quoted the whole page haha) leads me to believe the minoct is the lowest you can go even if both tables are the same:
This adjustment is done by monitoring knock retard (the amount of ignition delay added in by the ECU in response to knock sensor activity). More detonation means more knock retard and a lower “value” for the ECU's fuel octane rating."
I interpret it as thus: knock picked up by knock sensor creates knock retard which leads to a lower value of octane rating. Lower value of octane rating means more aggressive interpolation with minoct table.
 
I've done that Tony, mine still pulled timing as normal. It was back when I was learning to tune and I had both maps identical.

You were the guinea pig back then without even knowing LOL.
 
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