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93 octane with 10 percent ethanol

Does this affect Stoich and Lambda values relating to AFR?

Old 10-22-2013, 04:16 PM
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Found this.

This can be calculated:

sAFR = (%ofAdditive * sAFRadditive + (90-%ofAdditive) * sAFRgas) /100

where:
sAFR is resulting stoich AFR
%ofAdditive is amount in % of mass of additive (ethanol) mixed in
sAFRadditive is stoich AFR of additive (9 for ethanol)
sAFRgas is stoich AFR of base gasoline (14.7)

For a 10% mixture of ethanol to gasoline by mass the resulting stoich AFR is 14.13

So, for an engine that's tuned to certain AFR at a certain load and RPM on straight gas, the resulting (gasoline equivalent) AFR when running the mixture can be calculated as:

new AFR = tuned gas AFR * (gasoline stoich ratio) / blend stoich ratio

An engine tuned to 12.5 gas AFR will run at the equivalent of 13 gas AFR with a 10% ethanol blend.

Of course, when running in closed loop, the engine will run at 14.13 AFR instead of 14.7. O2 sensors (incl. widebands) donít measure AFR, but Lambda. Lambda is defined as actual AFR/stoich AFR. It's a ratio. In closed loop part throttle the engine is just running at Lambda 1.0, regardless of fuel. The same would be true for other Lambda values when running closed loop at WOT using a wideband. The engine would run at the tuned Lambda and everything would be fine. Open loop systems would need to be retuned for alcohol blends though.
Old 10-22-2013, 05:19 PM
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So .90 Lambda on a closed loop is 12.8 AFR with 10 percent ethanol on 93 octane? I found that the stoich value on 10 percent ethanol is 14.13 to 1, so 12.8/14.13 is .905 lambda, 13.2 being the AFR.
http://ls1tuningguide.com/files/freefiles/stoich%20conversion.pdf

Last edited by 9Thirty; 10-24-2013 at 10:09 AM..
Old 10-22-2013, 05:54 PM
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I can't believe that I only got one response on this topic. I did a little research on fuel Stoich values. Based on this, Stoich for pure 93 octane gasoline is 14.7, So on 93 octane with 10 percent Ethanol, my AFR is 12.8 at 6500 rpm and has a lambda value of .90/12.8 AFR because it has 10 percent ethanol (14.13 Stoich). .90 x 14.13 = 12.8 AFR on E10. .90 x 14.7 = 13.2 AFR on 93 octane.

If I run 100 octane, Stoich is 13.9 and I have a 12.8 AFR at 6500 rpm, it should compute like this. 12.8/14.7 x 13.9 = 12.1 AFR. 12.1/13.9 = .87 lambda. It helps a lot. I go from a 12.8 AFR on E10 and a .90 lambda to a 12.1 AFR and an .87 lambda. At 5500 rpm on 100 octane, I'm at 11.7 AFR, with a .84 lambda. I have Sunoco 260Gt 100 octane available right up the street (it 'aint cheap). This definitely affects your safety margin.

I pulled this fuel information off of a tuner site.

"Ever wonder if your airfuel will change with race gas? The answer is; Yes. Real gasoline has various different Stoich points due to the blend, how much ethanol is in it, etc. It is somewhere between 14.1 and 14.7. Finding the information on race gas isn't easy. It is not posted anywhere on the internet that I have found. VP does not publish it, nor does Sunoco (TurboBlue)."

"Several weeks ago I got in touch with the chemist at VP and got all the Stoich points of their fuels. Last week I got in touch with a Sunoco chemist and got the data from him as well. When I asked the guy from Sunoco why they don't publish the information on the TurboBlue website he said, "Eric, you're right, Stoichiometry is important. Fact is many people have no idea what it is; kudos to you for knowing."

"Unfortunately, many folks we talk to think the Stoichiometric air/fuel ratio is where they should set their fuel system at wide open throttle. So we are torn about posting or not posting Stoichiometry data because of that potential problem. Shocking right? Especially when you see how different the fuels are; Here is a list of the ones I have gathered."

Sunoco MO2X UL: 14.5
Sunoco 260 GTX: 14.4
Sunoco 260 GT: 13.9
Sunoco 260 GT Plus: 13.7
Sunoco Standard: 14.8
Sunoco Supreme: 14.9
Sunoco MO2X: 14.5
Sunoco HCR Plus: 14.8
Sunoco Maximal: 15.0
Sunoco MaxNOS: 14.9
Turbo Blue Unleaded (100 octane): 13.9:1
Turbo Blue Unleaded Plus (104 octane): 13.7:1
Turbo Blue 110: 14.7:1
Turbo Blue Advantage: 14.9:1
Turbo Blue Extreme: 15.0:1
VP Street Blaze 100: 14.16
VP C10: 14.53
VP 110: 15.09
VP C16: 14.77
VP MS109: 13.41

"Back to pump gas.... While I had the Sunoco guy's ear, I tried to get an answer about the Stoich of their fuel and to find out how much actual Ethanol is in it, when the label says up to 10%... Here are his comments..."

"I know plenty about pump gas, enough to say that there is no useful Stoichiometry data on pump gas. Composition varies WAY too much, regardless of brand/refinery/etc... especially on the lower octane grades. But I can tell you that Sunoco 94, which is very hard to find these days, will contain some ethanol."

"Per the first sentence, it will depend on the blend though. I would go out on a limb and say it is nearly 10% most of the time (keep in mind 10% is the max allowed by law). Street gas blends change all the time thanks to environmental requirements (fed/state/local), seasonal adjustments, and price pressures."

Last edited by 9Thirty; 10-24-2013 at 06:44 PM..
Old 10-24-2013, 07:18 AM
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As someone who is yet to understand some of those words, explain like im 5 what effect will filling up with non ethanol 93 gas have as opposed to the usuall 10% thats at every other station?

I found one station in charlotte and filled up my X5 and it made me happy, i think i got some power but more notably the consumption went down quite a bit.
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Old 10-24-2013, 07:32 AM
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That's one of the reasons I am installing an ethanol content sensor.

My plan is to tune on regular pump 93 then tune on a high quality -e85 such as vp-c85 or a similar high quality e-85.

I still have a lot of research to do on this subject but I really appreciate you doing some of that already!
Old 10-24-2013, 07:36 AM
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Meh, run a safe tune for pump gas and forget about it.

I run 1.4 bar on a 7.5:1 CR 3.4 with 93 octane of the better quality brands like Chevron, Texaco, Exxon, etc.

I run 21 degrees of timing without issue so far (no pinging - car is fairly quiet under boost and windows up)...... **cringing if timing is too high - Chris Carroll??.....**
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Old 10-24-2013, 08:08 AM
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Quote:
Originally Posted by Pezho405 View Post
As someone who is yet to understand some of those words, explain like im 5 what effect will filling up with non ethanol 93 gas have as opposed to the usuall 10% thats at every other station?

I found one station in charlotte and filled up my X5 and it made me happy, i think i got some power but more notably the consumption went down quite a bit.
It does not affect power, especially a unmodified non-performance car or SUV (X5). It only effects the safety margin concerning modified performance cars, forced induction especially (bigger turbo, intercooler, exhaust, PSI (Bar). If you tuned your car for the higher octane and advance the timing, you would develop more horsepower.

But I think that the real issue here is that most modified performance vehicles are tuned with a 14.7 Stoich value, when the reality is that most gasoline has a 10 percent ethanol content which will affect your AFR/Lambda calculation, because the fuel value is 14.13 versus 14.7 which is pure 93 octane. If you take a 12.8 AFR at 6500 rpm and compute the Lambda value 12.8/14.7, you end of with a .87 lambda. But in realty, the calculation should be; (12.8/14.13 = 93 octane with 10 percent ethanol) which is .90 lambda, 13.2 AFR.

Last edited by 9Thirty; 10-25-2013 at 07:24 AM..
Old 10-24-2013, 08:10 AM
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I doubt any tuners tune to stoch for WOT. If they do, they are in the wrong business!

Am I missing the point of this thread?
Old 10-24-2013, 09:01 AM
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Quote:
Originally Posted by Tippy View Post
I doubt any tuners tune to stoch for WOT. If they do, they are in the wrong business!

Am I missing the point of this thread?
The tuner should know your actual AFRs based on the fuel in your tank (91, 93, 100 octane).
Old 10-24-2013, 09:16 AM
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does this affect our tunes at any place other than idle? For example, when people say we should aim for 13.2/13.5 AFR for max torque with no boost and 12.2 under boost, should we adjust this richer to compensate for 10% ethanol?
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Old 10-24-2013, 05:06 PM
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Quote:
Originally Posted by s5uewf View Post
does this affect our tunes at any place other than idle? For example, when people say we should aim for 13.2/13.5 AFR for max torque with no boost and 12.2 under boost, should we adjust this richer to compensate for 10% ethanol?
The simple answer is, "Yes." Ethanol has an effect on octane rating thereby affecting your Lambda/AFR at every rpm. Especially since some of these pump fuels have even a greater ethanol contact than reported. Most gas stations report, "This fuel has no less than........ethanol." It could be 5, 10, 15 percent. Some tuners will not take this variable into consideration when setting your advance, boost, etc. etc.
Old 10-25-2013, 07:32 AM
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They don't take that into consideration because it doesn't matter. The fluctuation in AFR's during normal operation make it a moot point.

Now, tuning for E85 or your favorite flavor of race gas, the tuner has to account for due to different stoch values.

Unless I'm still not grasping why this is important?
Old 10-25-2013, 09:29 AM
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Quote:
Originally Posted by Tippy View Post
They don't take that into consideration because it doesn't matter. The fluctuation in AFR's during normal operation make it a moot point.

Now, tuning for E85 or your favorite flavor of race gas, the tuner has to account for due to different stoch values.

Unless I'm still not grasping why this is important?
You're not. Tune your car on the edge on 93 and put 91 octane in it with 10 or 15 percent ethanol on a cold day and drive it hard for about a half hour .........It will matter then. The fluctuation in your AFR can be as much a 1 to 2 points. Essentially going from a 12.5 at WOT to a 14 or worse.

Last edited by 9Thirty; 10-25-2013 at 02:34 PM..
Old 10-25-2013, 02:30 PM
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Yes, yes, yes, you tune to 91, 93, E85, 100LL, VP, Howell (not sure if still around ), or whatever.

My point is, you posted a bunch of "blends" of Sunoco that have varying stoch values.

As you pointed out and I did originally that there is a large fluctuation in AFR's making this a moot point. Point is, tuners don't tune to a "blends" of gas, rather octane points period.

I run 93 with 10% ethanol at 1.4 bar with AFR's in the high 11's without issue.

AFAIK.....
Old 10-25-2013, 05:40 PM
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Quote:
Originally Posted by Tippy View Post
Yes, yes, yes, you tune to 91, 93, E85, 100LL, VP, Howell (not sure if still around ), or whatever.

My point is, you posted a bunch of "blends" of Sunoco that have varying stoch values.

As you pointed out and I did originally that there is a large fluctuation in AFR's making this a moot point. Point is, tuners don't tune to a "blends" of gas, rather octane points period.

I run 93 with 10% ethanol at 1.4 bar with AFR's in the high 11's without issue.

AFAIK.....
They should tune to Stoich values. This thread wasn't about you and your particular car, it was hopefully a topic and a guide some members might find useful. I'm glad you're happy with your tune and your car.
Old 10-25-2013, 09:07 PM
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Ok, I'm not trying to argue with you, just pointing out why I don't feel it's a huge deal with say 10% ethanol:

1. If say 100 octane runs 13.9 stoch, and your calculated AFR results is say 12.5 at full boost (which you deem too lean for pure gas), it's not a big deal since the higher octane is keeping detonation at bay

2. Due to fluctuations of AFR's during normal operation, it's hard to maintain the "exact" AFR you believe the engine should be operating in. There will be milliseconds of too lean or rich as the engine passes through the RPM range.

3. Stoch is purely for emissions. Most engines run better from idle through WOT richer than stoch - rotaries run really rich vs their reciprocating engine counterparts.

Would love for Chris Carroll to chime in on this. It would be great if he weighed in on if we are really up against an issue or not. He tunes cars on 91 octane up to 1.5 bar IIRC.

Last edited by Tippy; 10-25-2013 at 10:44 PM..
Old 10-25-2013, 10:05 PM
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Quote:
Would love for Chris Carroll to chime in on this. It would be great if he weighed in on if we are really up against an issue or not. He tunes cars on 91 octane up to 1.5 bar IIRC.
I would love it if anyone chimed in, that's why I started the thread. I think in your case EFi, you're much less prone to a lean issue, but us CIS guys are infamous for lean conditions, then throw in crappy gas........Not saying detonation, but engine damage over a period of time depending on how much it is driven and how spriited the driving.

Last edited by 9Thirty; 10-26-2013 at 01:08 PM..
Old 10-26-2013, 05:31 AM
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Yeah me too, because I never thought about this and wonder if you're on to something - hence me spurring ideas for discussion.
Old 10-26-2013, 06:09 AM
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Alcohol drag cars? Ethanol is alcohol. If you fatten your car to run on the ethanol mixture you buy you will be fine and make good power safely.
The oxygenators they add to gas is crap and makes the gas go 'Bad' quickly even in sealed containers.

Old 10-26-2013, 04:43 PM
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