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 Post subject: Stoich for gasoline
PostPosted: Tue Mar 09, 2021 9:02 am 
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I've see a lot of debate on that point, here's one post I found helpful so I'm posting to save it:
Quote:
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."


One point to add to it is ethanol is expensive so I would guess they add as little as they can and meet EPA rules and 10% is the max they are allowed, not the actual % and probably not the norm so stoich is not lower than 14.1 and with pump gas not higher than 14.7 but I have no idea where in that range it falls....and the error will wash into the VE table during tuning. I try to stick to 1 brand fuel because I tend not to use closed loop.


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