Stoich AFR, adding flex fuel

[JoshBoody]

Built LS3 has already been tuned on 93oct, which I will be adding a flex fuel sensor. I only want to change the flex tables without re-tuning VE and MAF.

Since it was tuned on 93oct (E10), the ECU targets 14.7, but in reality its closer to 14.1. If I want to keep the same airflow should I set the Stoich AFR at 14.1 for E0 scaling from here? Otherwise ECU will add slightly more fuel than needed scaling from 14.7.

[2xLS1]

Is the 93 E10 or 100% gas?

[JoshBoody]

Is the 93 E10 or 100% gas?

Pretty sure the 93oct gas is E10... car is in TX and I will transferring it to AZ, thus the need for flex since we only have 91oct.

[2xLS1]

Just use the stoich table from a FF truck. 14.1 is about the stoich for E10. And as the elevation goes up the less octane is required NA. Probably why only 91 is available in AZ.

[JoshBoody]

I know the stoich for each E% and E38 ECM will have this populated already. My question pertains to scaling the table with 14.1 as E0, since it was tuned on E10 (most gasoline) without flex enabled... meaning ECM is calculating fuel based on 14.7 instead of 14.1. If I go from no flex to flex the ECM will now target 14.1 skewing the whole range by about 4%.

Is my thinking accurate?

[5FDP]

The nice thing about HP Tuners is that you can try something and change it if it doesn't work.

Start with a regular flex fuel table and see what yours trims do, then change it if needed.

[GHuggins]

I know the stoich for each E% and E38 ECM will have this populated already. My question pertains to scaling the table with 14.1 as E0, since it was tuned on E10 (most gasoline) without flex enabled... meaning ECM is calculating fuel based on 14.7 instead of 14.1. If I go from no flex to flex the ECM will now target 14.1 skewing the whole range by about 4%.

Is my thinking accurate?

Stoic will change and it'll run different, BUT you might be surprised that trims don't change that much. It should idle a little smoother and burn a little better, but you probably won't see that much of a change in anything other than commanded. You'll need to watch out on your PE target. Might want to rework the math on that one, but other than that....

And to clarify on the above there is no need to put anything other than regular correct values into the stoic table to keep fueling right due to that, but it would actually be the other way around in relation to what you're asking. You tuned - more than likely 8ish% ethanol fuel - to 14.678, so if you wanted to make the 14.3ish the same you would instead add to the stoic table. Personally I would leave it set right and if you needed to touch up the MAF any at all, it's easy enough to do so.

[JoshBoody]

Oh yeah, you are right. Tuning at 14.7 for E10, once ECM reads E10 it will target 14.1 and have to remove fuel with -trims to get to stoich. So you'd have to scale >14.7 at E0 for the same fuel volume as the baseline tune.

[GHuggins]

Unless you just run or only have cheaper stations around there, it's more than likely going to be 7 to 9 % ethanol as E10. That's what I see with all of the ethanol tunes I do. It's just stations trying to be cheaper that are running up to 12%. I've even had a couple of customers getting straight 0 % at regular pumps which I found really interesting. Those were mainly guys further south in the US. Just depends on what your "E10" winds up being. I would just set stoic to a regular transitioning stoic scale and not worry about trying to skew it. Just my .02 worth...

[JoshBoody]

I gotcha, thanks for the input.

Reason for asking is because this car is loud and I'm in an area where it will be tough to tune, so I wanted to get it as close as possible first. IDC is at 85% already, so don't want it too rich during PE... will target about E25, figure that will get me to 93+ oct.
I take it another method could be estimating MAF, subtracting about 3%. I think VE doesn't matter when in PE IIRC.

[2xLS1]

Unless you just run or only have cheaper stations around there, it's more than likely going to be 7 to 9 % ethanol as E10. That's what I see with all of the ethanol tunes I do. It's just stations trying to be cheaper that are running up to 12%. I've even had a couple of customers getting straight 0 % at regular pumps which I found really interesting. Those were mainly guys further south in the US. Just depends on what your "E10" winds up being. I would just set stoic to a regular transitioning stoic scale and not worry about trying to skew it. Just my .02 worth...

We have E0 at just about every gas station in Okla. Many have E0 in 87,89,and 91. They will also have E10 usually only in 87. The Caseys stations have E15 they call Super 88.

[GHuggins]

We have E0 at just about every gas station in Okla. Many have E0 in 87,89,and 91. They will also have E10 usually only in 87. The Caseys stations have E15 they call Super 88.

Well that's good to know. I know a couple of guys I was doing E tuning on started with around 7 to 9 % then all of a sudden went to 0. Had me wondering if the sensor went out, but found it reading correctly.

Everywhere around me has around 10 to 12 % and then the "0%" is actually 6% unless you drive an hour to a bigger city.

[Alvin]

Built LS3 has already been tuned on 93oct, which I will be adding a flex fuel sensor. I only want to change the flex tables without re-tuning VE and MAF.

Since it was tuned on 93oct (E10), the ECU targets 14.7, but in reality its closer to 14.1. If I want to keep the same airflow should I set the Stoich AFR at 14.1 for E0 scaling from here? Otherwise ECU will add slightly more fuel than needed scaling from 14.7.

There is only a 4% difference between the two. You could just blanket scale the VVE/MAF by 4% to make up for it when the flex sensors actually sees pump gas at E10.

But really 4% is inside a window of how rich/lean it will be from day to day. I wouldn't worry about it to much.

Hell they can get away with putting 10% E in normal every day non flex cars cause it makes such a small difference in fueling. 14.7-14.1 sounds like a lot.. but 4%

[JayRolla]

I gotcha, thanks for the input.

Reason for asking is because this car is loud and I'm in an area where it will be tough to tune, so I wanted to get it as close as possible first. IDC is at 85% already, so don't want it too rich during PE... will target about E25, figure that will get me to 93+ oct.
I take it another method could be estimating MAF, subtracting about 3%. I think VE doesn't matter when in PE IIRC.

I think your overthinking the octane a bit. At high altitude that 91 will be fine. I am guessing you will be in a high-altitude part of AZ if you only will have 91. I've been tuning on 91 all my life. I wouldn't spend the money on a flex fuel kit just to run e25, plus the hassle of mixing. Get injectors and do it right. I run e70-e85 at high altitude on stock fuel pumps. On 91 I hit 19* timing at 10-12psi with zero knock. My pulley setup should be good for 15psi. You're going to lose 3psi of boost moving up in altitude. Worse case you might have to pull 1-2* but I bet you won't even have to change anything at high altitude with 91 octane.

[JoshBoody]

Thanks guys!

We are only at 1,000 to 1,500ft and all AZ has 91oct. This will be a track car seeing higher ECT and constant WOT, so the more conservative I can be the better. In my experience, 350whp LS1 and turbo BMW, AZ 91oct is pretty crappy... I saw pretty significant improvements on E30. This new car is a very strong, 500+ whp stock bottom end LS3, so I'd like to be very careful.

If I purchase larger injectors with flow data, is is possible to just enter this data into the tune without adjusting VE/MAF? I've never tuned new injectors before. Haven't received the car yet, but supposedly the tuning is pretty spot on and with a 235-ish cam I don't want to touch airflow or idle.

This is a 2011 Vette, can the fuel pump support 520-ish whp on E70?
I would go a little leaner on ethanol, but I do not see a composition multiple table for blending gas to alcohol AFR, so I'd be a little uncomfortable doing this.

[JayRolla]

Thanks guys!

We are only at 1,000 to 1,500ft and all AZ has 91oct. This will be a track car seeing higher ECT and constant WOT, so the more conservative I can be the better. In my experience, 350whp LS1 and turbo BMW, AZ 91oct is pretty crappy... I saw pretty significant improvements on E30. This new car is a very strong, 500+ whp stock bottom end LS3, so I'd like to be very careful.

If I purchase larger injectors with flow data, is is possible to just enter this data into the tune without adjusting VE/MAF? I've never tuned new injectors before. Haven't received the car yet, but supposedly the tuning is pretty spot on and with a 235-ish cam I don't want to touch airflow or idle.

This is a 2011 Vette, can the fuel pump support 520-ish whp on E70?
I would go a little leaner on ethanol, but I do not see a composition multiple table for blending gas to alcohol AFR, so I'd be a little uncomfortable doing this.

That sucks they have such low octane at 1k feet. Kind of surprising actually.

If you get good injectors like ID's the data is pretty spot on. You might need to slighly adjust VVE and MAF for fuel trims but thats super easy. With you being at 85% IDC already I would not add e to the equation. I know you can push them further N/A than boosted. Plus if you are already commanding .85 at WOT, even on E I wouldn't go much leaner.

You might need to verify but I think the stock fuel pump in that is a 255lph. Should support 550ish on e85 N/A so you would be pushing it. Could always add a boost a pump if fuel pressure drops too much. We have K&G's/Maverick here in CO and they always e70 so I stick to them since Im on stock pumps (CTS-V has dual pumps stock).