What you should know about octane and your A/F
04-07-2009, 06:54 PM
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What you should know about octane and your A/F
This was on the other forum but I found Eric Brook's post very interesting. Makes you wonder if a lot of tuners are running lean on the race gas tunes. It certainly makes me re-think what is the 'right' a/f range to shoot for with a specific set-up. I'm beginning to wonder if the fact Greg has been been tuning my car to 10.x for awhile now is the reason it's still in such good shape...:idea:
The entire thread is a good read.
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 though.
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 -
Quote:
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...
Quote:
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.
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 though.
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 -
Quote:
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...
Quote:
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.
04-07-2009, 07:51 PM
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Join Date: Nov 2007
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Posts: 1,699
Sometimes it is better to think in terms of Lambda instead. If your wideband reads 11.5 on your 93 octane street tune and on your Race tune with GT260 Plus reads 11.5, those are NOT the same air fuel ratios. All widebands actually read in terms of lambda and then apply the Stoich for regular gasoline and then display that on your wideband. That 11.5 on your street tune is 11.5/14.64=0.785 Lambda. Now that same 11.5 reading on the gauge when running GT260 Plus is actually 10.75 since Stoich for this fuel is 13.7 (13.7*.0785).
I guess what I am trying to get at is that as long as your tuner is properly adjusting your tune for the different Stoich points for your particular race fuel of choice then you should be ok. What can be dangerous is just running race fuel and not being mindful of the changes in air fuel that will happen without adjusting the tune.
I guess what I am trying to get at is that as long as your tuner is properly adjusting your tune for the different Stoich points for your particular race fuel of choice then you should be ok. What can be dangerous is just running race fuel and not being mindful of the changes in air fuel that will happen without adjusting the tune.
Last edited by modaddict; 04-07-2009 at 08:06 PM.
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