jrwood

Quick question: I have read that the C7 ECM can detect ethanol in the gas and increase torque management. (pull power) I have a feeling this is true as I have done a few different trials and seen different results.

2014 C7 non-Z51 Auto
Houston, TX area

Three Mixes
Standard pump gas: 93 pump gas (10% ethanol blend)

Standard pump gas: 93 pump gas (10% ethanol blend) + Boostane/Torco Additive = Octane 104

Sunoco GT Plus 104 (no ethanol)

I have found the car made more power and decreased quarter mile times with the Sunoco GT Plus 104.

I thought the 93 pump gas with additive would equal the Sunoco fuel but I think that the ECM is detecting the ethanol from the 93 pump and pulling power out some.

I had the 93 + additive tested in Houston and it did have an octane rating of 104 but I think the ethanol is not allowing the car to make as much power as the Sunoco 104.

Wanted your thoughts on this as I know I'm splitting hairs on a stock tune but before I go any further wanted to make sure I understand fully what each fuel I have access to is doing in the car.

I assume once I have the car tuned on one of these fuels the tuner can override the torque management.

Thanks!
John

MitchAlsup

The problem with Ethanol is that it contains less energy per unit weight--that is, while Ethanol has high Octane and can increase the octane of the fuel it becomes part of, it reduces the power because power is a function of the energy density of the fuel.

The ECU does not pull timing, the power is simply not in the fuel--and nothing the ECU does can alter this fact.

OH, and BTW, If the 104 Octane makes more power, it DECreases 1/4 mile times.......

RoadRebel

C7s do not have an ethanol sensor.

The Sunoco GT260 fuel you used is an oxygenated race fuel that contains 4.8% oxygen and is where the added power came from.

RussM05

Ummmm. Not true.

The front O2 sensors detect rich or lean AFR and adds or subtracts fuel to achieve targeted air/fuel ratio which is necessary to make the most power. E10 is about 14.1 stoichiometric and that is actually what the C7 are programmed to use. If there is more or less the ECU will add/subtract fuel according via the long term fuel trims (LTFT).

Actually, total energy or power is limited by the amount of oxygen in the air not the fuel. You can add more fuel, but if there isn't the oxygen there to mix with, it won't make more power.

Top Fuel cars use nitromethane as their fuel that has oxygen in it, so the more fuel you can inject (within limits), the more power the engine will make. They use 15 gallons in a quarter mile.

Kingtal0n

So wait, you are saying,

The C7 engines use a wideband sensor for closed loop operation wide open throttle?

And also,

If I install an aftermarket wideband such as AEM, I will see 14.1:1 air fuel ratios during normal cruise situations as a target?

Be sure to clarify any misleading information

Higgs Boson

C7 use narrowbands that switch at stoich. Stoich depends on what fuel is in the tank. Stoich for E10, which is most likely in your tank, is 14.1.

GM realizes this so they put 14.1 in the stoich table, which the fuel trims (not to be mistaken for O2 sensors) try to achieve. So if your O2 sensors are switching at stoich and your stoich table is programmed to something other than stoich for whats in the tank, you are going to have unnecessary fuel trims.

Widebands are only different in that they can report a specific air fuel ratio (lambda actually) between a "wide"er range of voltages, which means they are capable of measuring your exhaust mixture at full throttle as well as part throttle (narrowbands only work right at part throttle). Mustangs stay in closed loop during WOT and use widebands, Chevys do not.

Kingtal0n

Okay so to clarify,
This,

Is incorrect. Since "chevys do not use closed loop during WOT".

And this,

Is right? So my AEM aftermarket wideband will show 14.1:1 while cruising if installed? On a factory vette engine running factory electronics? I find that hard to believe but,, if you say so... The reason I don't believe it is because that would mean chevy would need to re-design the narrowband Oxygen sensor. Since they only work at 14.7:1. Unless you are saying that chevy has a wideband, and it is programmed to see stoich at 14.1:1, that I can see happening.

Higgs Boson

you have to realize that oxygen sensors measure LAMBDA, AFR is a conversion from lambda.

lambda 1.0 is stoich. narrowbands switch around stoich. an aftermarket wideband switches around stoich and each different one will display (convert to) AFR differently.

One will show stoich at 14.57, one at 14.68, one at 14.7, etc. This is where people get confused. All of them are lambda 1.0, which for E10 is 14.1.

So when the display box that comes with your wideband says 14.6, it is wrong. 14.6 = 14.1, if you are running E10 of course.

Kingtal0n

Oh my. So a vette engine DOES come with narrowband sensors.... and DOES switch from .002~volts to 1.002~volts around 14.1:1 when using E10. Very nice! Thats exactly what I needed to know.
Thanks for clearing it up! I was worried for a minute they had OEM widebands... shudders*

Higgs Boson

i WISH they had widebands.

Shaka

No tuner that I know of has a fuel tester (chromatograph $8000 to $14000) incudes octane measurement. Everytime you put in gas, the fuel properties will be different even from the same pump the next time you fill. Octane will vary 4 points, more or less. You can get 20hp more or less from one day to the next just because of the fuel.
All the materials that go into the blends can cause the specific gravity to vary and that can affect how the fuel behaves in the injectors and the combustion chamber. This is not your 60s muscle car.
The use of ethanol as an octane booster is not a good idea. Octane has many structural isomers that differ by the amount and location of branching in the carbon chain which determine the octane rating. Vaporization destroys most of them which lowers octane rating. Only use top brand name gasolene. SUNOCO is the best.

OEM ECUs are designed for crap fuel. Be very careful when you mess with them. You are often running on fuel of a much lower octane rating than you think. If you tune for race fuel, you dare not use pump fuel.

Maybe you have wondered sometimes why the engine is running hotter than normal. Well, it may not be your cooling system or the engine itself, it may be that you’re running a different fuel blend with a lower effective octane and didn’t know it. So you were getting by fine before but now because of the differences in the pump gas you’re using, this tank isn’t working so well.

Even racing fuel has ethanol. If you plan on running your car hard, better invest in some decent fuel. No pump gas will do especially in high humidity regions. Just letting your 10% ethanol gas stand will alter it's octane rating which can do harm to your engine.
Always gas up before rain storms and definately not during. When your intake is hot, vaporization occurs which further reduces octane rating. It stays cooler on track days.
Always purchase high quality fuel, test for water and alcohol before purchase, follow necessary precautions, and refill tank often.
Reputable gas stations will give you a read out of their tanks water content.
Replacing fuel in your tank every 1-2 weeks will usually maintain the octane rating by limiting the occurence of water absorption into the gas tank.

RussM05

Good explanation.

I suggest to members of the forum that are interested in learning more about this subject buy Greg Banish books on Tuning. There are a couple of other books from other authors, but I think Greg's books are very good reading on this subject. However, to my knowledge there are no books out specifically on the E92 ECU and per Greg's posting on the HP Tuner's forum, its much more complex.

Greg also posts frequently on the HP Tuner's forum and so does Higgs Boson.

The new ECUs are extremely sophisticated. To keep it simple, they monitor almost every variable to calculate the air mass in the cylinder then its a fairly simple calculation to determine the amount of fuel to inject to achieve the targeted stoichiometric. In closed loop, the O2 sensor reads the exhaust to see if it was rich or lean, stores that info as fuel trims which are referenced in the future. When I scanned my 2014 LT1, the fuel trims were all very low...most cells were 1-2% in non-WOT areas.

On my 2005, the last fuel trim before it goes from closed to open loop is used which can create problems at WOT. Not sure how the new E92 handles fuel trims in open loop WOT conditions since targeted A/F ratio is out of range on the narrow band.

tblu92

Yes the C7 is programmed to run at a 14.10 AFR in closed loop--You are correct in assuming that the C7 02's are different than the DI Silverado 02's that are still programmed at 14.68 in closed loop-My guess the C7 's are more sensitive and made to adjust to the 14.1

Higgs Boson

still don't get it, do you?

how is the C7 "more sensitive?"

no car is programmed to run at a certain afr. they are programmed to run at stoich for whatever is in the tank (at part throttle).

are you under the impression that truck calibrators are also corvette calibrators? you can have quite different settings come on the same car with different operating systems much less two totally different models produced in different places and created by different groups of people.

who cares if the stoich tables are different, it means nothing. closed loop fuel trims will trim it to whatever stoich is for the fuel in the tank, and it isn't going to be exactly 14.1 or 14.68 no matter what car you are driving. if you fill a truck up and a vette up at the same pump they are going to run at the same stoich value just with different fuel trim values.

Shaka

http://jalopnik.com/carmakers-want-t...eca-1699132210

EcoBrick Bob

Because Ethanol has less BTU's it takes more fuel to get the same amount of power. However, Ethanol has a much higher octane rating. Thus if you would run pure ethanol, you would need considerably more fuel. I have been told that to get the most out of a boosted engine running ethanol, you may need 50% more fuel delivery to the cylinders. Because your engine can be advanced higher and handle increased boost due to the octane rating, you develop considerably more HP when tuned for ethanol. There are some other constraints besides fuel delivery volume. You have to consider how strong your engine is, like pistons, rods, crank and valve train items, as a starter.

Ask a knowledgeable tuner as to what that is, and what he can do within the engine limitations, mods included.

In stock configuration, there is a limit as to how far the ECM will adjust for high octane racing fuel, without tuning. You might see a 10-15 hp variance between 87 and the best gas you can buy. A tuned engine that is otherwise stock would add maybe another 40 hp at most, but probably less.

tblu92

STOCK tune file for closed loop AFR on a non E85 Silverado and an E85 equipt model----Difference being the non eq uit one does not have a flex fuel sensor so even if the pump gas has 10% ethanol in it -- The ECM does not make adjustments for it
A C7 however does as it's closed loop fuel shows 14.10 throughout the entire AFR table--even with 0% ethanol

SILVERADO FUEL TABLE
LABELS Stoichiometric AFR (Air/Fuel Ratio)
Ethanol % {link: GM.E85PCT} Value
0.0 14.678224
6.2 14.322267
12.5 13.965822
18.7 13.609376
25.0 13.252443
31.2 12.896486
37.5 12.540529
43.7 12.183595
50.0 11.827638
56.2 11.471193
62.5 11.114259
68.7 10.757814
75.0 10.401857
81.2 10.045899
87.5 9.688966
93.7 9.332520
100.0 8.976563

C7 STOCK fuel table
LABELS Stoichiometric AFR (Air/Fuel Ratio)
Ethanol % {link: GM.E85PCT} Value
0.0 14.108400
6.2 14.108400
12.5 14.108400
18.7 14.108400
25.0 14.108400
31.2 14.108400
37.5 14.108400
43.7 14.108400
50.0 14.108400
56.2 14.108400
62.5 14.108400
68.7 14.108400
75.0 14.108400
81.2 14.108400
87.5 14.108400
93.7 14.108400
100.0 14.108400

Self explanatory showing the difference in AFR's of a trck DI engine VS the C7 DI engine---