Alternative fuel enrichment

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David Redszus
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Alternative fuel enrichment

Post by David Redszus »

As is often the case, an engine built for certain fuel blend must be run on some
other blend, either due to dyno issues, track regulations, or availability.

Now the problem becomes to determine which alternative fuel will perform similar
to our original fuel and is a change in enrichment necessary?

Which fuel will run richer, which will run leaner? And by how much?

Following is a list of some Sunoco and VP fuel blends and their properties.

Can we try to rank them in order from lean to rich mixture?
Assume the same jetting or mapping.

Blend......SpG.......Stoich......O2 %
Supreme...0.715.....15.0........0.0
HCR+.......0.739.....14.8........0.0
260GTX....0.763.....14.6........3.7
260GTX....0.764.....14.1........3.3
SV-05.......0.745.....13.9........4.7
Q-16........0.716.....13.4........9.4
C-16........0.735.....14.7........0.0
CHP+.......0.742......11.7......18.3
C-85........0.794.......9.2......32.0
MS109reg..0.720......13.4.......9.3
swampbuggy
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Re: Alternative fuel enrichment

Post by swampbuggy »

Hello David, is this a test / quiz for us readers to attempt ? Mark H. :?
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Re: Alternative fuel enrichment

Post by JCR »

swampbuggy wrote: Sat Jan 28, 2023 10:28 pm Hello David, is this a test / quiz for us readers to attempt ? Mark H. :?
Yes, it is. Get cracking... :)
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Re: Alternative fuel enrichment

Post by HQM383 »

David Redszus wrote: Sat Jan 28, 2023 6:43 pm As is often the case, an engine built for certain fuel blend must be run on some
other blend, either due to dyno issues, track regulations, or availability.

Now the problem becomes to determine which alternative fuel will perform similar
to our original fuel and is a change in enrichment necessary?

Which fuel will run richer, which will run leaner? And by how much?

Following is a list of some Sunoco and VP fuel blends and their properties.

Can we try to rank them in order from lean to rich mixture?
Assume the same jetting or mapping.

Blend......SpG.......Stoich......O2 %
Supreme...0.715.....15.0........0.0
HCR+.......0.739.....14.8........0.0
260GTX....0.763.....14.6........3.7
260GTX....0.764.....14.1........3.3
SV-05.......0.745.....13.9........4.7
Q-16........0.716.....13.4........9.4
C-16........0.735.....14.7........0.0
CHP+.......0.742......11.7......18.3
C-85........0.794.......9.2......32.0
MS109reg..0.720......13.4.......9.3
Which one is the original fuel?
Is the original tune 10% rich of stoich?
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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Re: Alternative fuel enrichment

Post by rgalajda »

14.7:1 AFR means the mixture is 14.7 parts air to one part fuel.

Pure gasoline has a stoichiometric ratio of 14.7

E85 stoichiometric ratio is 9.8

Methanol stoichiometric ratio is 6.4

So it’s obvious if you switch to E85 fuel ,the delivery would have to be enhanced. For a carburetor this means much larger fuel jetting.

You can rate these blends by stoich, 15 being the richest .

The percentage of oxygenated should be already figured into the stoichiometric ratio.

Some of these fuels listed that are highly oxygenated will have an estimated stoichiometric ratio.
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Re: Alternative fuel enrichment

Post by juuhanaa »

I dont have the answer, but i would like to ask a question. What would be the value when calculating the differences in fuel volume flows and adjusting the enrichment based on that? And how to address the added oxygen in the calculus? All i know is that my car has run rich mixture prior changing from ELF to pump gasoline, and guys say the fuel at the pump is not of uniform quality, and therefore not suitable for aviation. :lol:

When i see excel, which could probably do the calculation for us, i think that the differences in different fuels and their affects to mixture motion, charge cooling, intake dynamics and combustion still need to be evaluated separately. I have my conserns when dealing things like separately and volumes, but thats partly because i also have problems in comprehense these things... Im not a fan of trial and error, error, error and error. :D Regards,



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Re: Alternative fuel enrichment

Post by Truckedup »

This is subject is interesting despite my limited knowledge....I always used VP C12 in my vintage land speed bike...it did the job and set several speed records....a local dyno guy involved in bikes and 1000 hp sleds complains that race gas is often not up to specs on RVP ,he has testing equipment...So there may be differences even when using the same type..
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire
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Re: Alternative fuel enrichment

Post by RDY4WAR »

Same jetting or mapping, as read by the O2 sensor in the exhaust, using Supreme as the reference sample...

C-85...........-31.9% leaner
CHP+..........-19.1% leaner
Q-16...........-10.5% leaner
MS109reg.....-10.1% leaner
SV-05..........-3.5% leaner
Supreme.......reference
260GTX(2)....+0.004% richer
C-16...........+0.01% richer
HCR+..........+0.02% richer
260GTX.......+0.04% richer
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Re: Alternative fuel enrichment

Post by panic »

Stoichiometric means chemically correct. All energy present is liberated.
Running WOT @ 14.7:1 (by weight, since gasoline weighs approximately 640 times as much as air, the proportion by volume if fully vaporized is about 9,400:1) leaves much power on the table.
Light tip-in at cruising speed @ 14.7 will give lazy response compared to 14.0:1
Running 14.7:1 @ high vacuum low load cruising wastes gas.
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Re: Alternative fuel enrichment

Post by rebelrouser »

juuhanaa wrote: Sun Jan 29, 2023 6:29 am I dont have the answer, but i would like to ask a question. What would be the value when calculating the differences in fuel volume flows and adjusting the enrichment based on that? And how to address the added oxygen in the calculus? All i know is that my car has run rich mixture prior changing from ELF to pump gasoline, and guys say the fuel at the pump is not of uniform quality, and therefore not suitable for aviation. :lol:

When i see excel, which could probably do the calculation for us, i think that the differences in different fuels and their affects to mixture motion, charge cooling, intake dynamics and combustion still need to be evaluated separately. I have my conserns when dealing things like separately and volumes, but thats partly because i also have problems in comprehense these things... Im not a fan of trial and error, error, error and error. :D Regards,



-juhana
Been drag racing since 1974. Over the years I have seen guys try several types of fuel and get varying results. The reason is the original post, different fuels have different burn rates and other prosperities. To really find out if a specific fuel will help or hurt your combination you have to take into account those differences and make adjustments. As an example, I helped a buddy build a 540 BBC and his goal was 900HP we pulled it on 110 gasoline and got 895HP tried spacers etc. and that was it. So he had the idea to try some 114 gas, it made 10hp less. We should have adjusted jets and timing, but our dyno time was up for the day.
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Re: Alternative fuel enrichment

Post by rgalajda »

You can't safely run 14.7:1 AFR at WOT

You can run up to 16:1 at cruising speed without a lazy response on some engines. Vacuum advance employed. Ignition timing of 40+ degrees at cruising speed is important. Just witness the AFR of some of the factory carbs . Quadrajet and Holley

Higher octane rating gasoline then the motor needs usually results in a slight drop of horsepower.
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Re: Alternative fuel enrichment

Post by RDY4WAR »

rgalajda wrote: Sun Jan 29, 2023 1:27 pm
Higher octane rating gasoline then the motor needs usually results in a slight drop of horsepower.
False. The octane has no impact on power aside from allowing more power if the engine was octane limited previously.

Take a 10.5:1 compression 383ci SBC making 450-500 hp NA on premium pump gas. Swap the pump gas for VP C25 (>117 AKI), and it'll gain response and power. Swap in Sunoco Supreme (112 AKI) and it'll likely lose response and power. All the octane references is the auto-ignition point of the end gases. Once the mixture is lit, the octane is mostly irrelevant. The distillation, RVP, and oxygen % are far greater factors than octane when it comes to response and power.

The myth that too high of octane kills power likely came from people putting in a fuel that has a high distillation curve and low RVP, like Sunoco Supreme or VP C16, that doesn't vaporize as readily, leave more liquid fuel droplets in the chamber that hurts combustion efficiency. Then mistakenly think the octane is hurting the power when the real issue is a mismatch of fuel to application.
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Re: Alternative fuel enrichment

Post by HQM383 »

RDY4WAR wrote: Sun Jan 29, 2023 2:42 pm
rgalajda wrote: Sun Jan 29, 2023 1:27 pm
Higher octane rating gasoline then the motor needs usually results in a slight drop of horsepower.
The distillation, RVP, and oxygen % are far greater factors than octane when it comes to response and power.
Is the H:C ratio a factor too?
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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Re: Alternative fuel enrichment

Post by Tom68 »

RDY4WAR
The myth predates race fuels

People erroneously believed all higher octane fuels burned slower. The irony is that a lot of them used that error to conclude that adding Diesel to gasoline would increase octane. Of course it lowers it, hell Diesel doesn't even need a spark to ignite.
Ignorance leads to confidence more often than knowledge does.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
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Re: Alternative fuel enrichment

Post by HQM383 »

David,
This is a good thread that will likely fizzle out when the quiz answer is correct, which maybe already be due to RDY4WAR reply.

maybe this thread could be expanded upon to extend people’s knowledge of fuels fit for purpose beyond octane rating.

We could;

1, Build a few virtual engines and select the best fuel for engine purpose. Maybe x1 n/a, one boosted and one nitrous.

2, start with a homologated class fuel and build an engine around that for best power for purpose.

The sbc is the most common engine out there for us hot rodders, builders, racers and hobby guys so all engines based on say the venerable 383ci sbc.
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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