Fuel Quality Testing

[No Limits]

I have built a few recent street engines for various configurations and almost all of them are running just pump 93 octane. I have had some tuning issues with these engines and I cannot seem to find the cure. Not knowing where all these customers get their fuel from and what brand it is and if they use the same gas station every time. I been researching a little about a fuel octane tester. I understand that gas stations are inspected and what not but is the fuel really what is advertised? Because of my tuning issues recently and some of these engines being expensive and high horsepower how do I know that the fuel they use isn’t the problem? Has anyone tested fuel octane with a tester of some kind? Or some other means of testing fuel? If so what is best? Thanks

[Kevin Johnson]

Maybe a better question for the audience here is what carefully formulated aftermarket fuels do they suggest to tune with?

The fuel supply that customers use can vary by tanker load (weekly?). You need to shift the onus to the user to ensure their gas supplies meet the quality of what you tuned them with.

Provide a list of certified fuel testing labs. Run a test on each batch of barrels of fuel you bring in and save those results.

[rebelrouser]

Lots more to fuel than just octane. I use specific gravity, and this test kit. Pump gas goes bad quick, and reed vapor pressure is just as important as octane, when tuning a pump gas engine. Liquid fuel does not burn, it has to vaporize. They change the reed Vapor pressure a couple times a year at the pump. Also a test kit to see what the alcohol content is. Alcohol is mixed by the jobber not the refinery, at least that is what I was told, so the content varies a lot. Most manufactures are requiring these types of fuel tests on drivability issues when cars are under warranty.


https://www.otctools.com/products/gasol ... esting-kit

[RCJ]

If the specific gravity of fuel A is .711,fuel B .728. Fuel b should require larger jet?

[David Redszus]

I been researching a little about a fuel octane tester.

Don't waste your time and money.
The only legitimate octane testing is performed using a Waukesha Octane Test engine, which is found at every refinery but seldom elsewhere. Most octane numbers are estimated from the composition of the fuel.

I understand that gas stations are inspected and what not but is the fuel really what is advertised?

No they are not. The signage at the pump is totally meaningless and should be ignored.
Pump gas should never be used in an expensive performance engine. Pump gasolines are totally inconsistent and subject to constant change. The EPA requires changes in certain specifications on a monthly, state by state basis. But that is measured at the refinery, not at the pump.

how do I know that the fuel they use isn’t the problem? Has anyone tested fuel octane with a tester of some kind?

Recently I tested fuels for the Formula SAE program at Michigan and Nebraska. I tested three fuels from Sunoco: 260GT, E-85, and 93 octane pump gas. Comparing several years of data for the "same" fuels, I can assure everyone, they are never the same.

The largest variances were found with 93 octane pump gas. Both the SpG, stoich and alcohol content varied considerably, as did the di-electric values. Previous lab analysis has confirmed the extreme variances of the component composition as well.

E-85 could actually be anywhere from E-70 to E-87. And the alcohol is prone to water absorption.

The most consistent of the fuels tested was 260GT race fuel. It had a lower alcohol content with much more consistency regarding other variables.

[Mike Laws]

I have built a few recent street engines for various configurations and almost all of them are running just pump 93 octane. I have had some tuning issues with these engines and I cannot seem to find the cure. Not knowing where all these customers get their fuel from and what brand it is and if they use the same gas station every time. I been researching a little about a fuel octane tester. I understand that gas stations are inspected and what not but is the fuel really what is advertised? Because of my tuning issues recently and some of these engines being expensive and high horsepower how do I know that the fuel they use isn’t the problem? Has anyone tested fuel octane with a tester of some kind? Or some other means of testing fuel? If so what is best? Thanks

All good information provided here. The consistency of pump gas is horrible which makes it tough on performance engine builders and their customers. I dyno tested a high end 632 a few years back that was purpose built for pump gas. The engine builder brought 15 gallons of 93 from a local station and tuned the engine to that fuel. The next day, he brought 5 gallons of 93 from another station and the engine was down nearly 100hp and sounded terrible. He started removing the valve covers to look for issues and I asked if he had any fuel leftover from the day before. He did. He put the valve covers back on, replaced the fuel with yesterday's 'batch' and the 100hp came right back. He immediately took the engine off the dyno saying that he was going to "knock at least a point of compression out of it and call my cam guy".

If you're locked in to using pump gas, I suggest modifying your combination to run with the worst 93 you can locate. You'll give up a little power, but the end justifies the means.

[GARY C]

I been researching a little about a fuel octane tester.

Don't waste your time and money.
The only legitimate octane testing is performed using a Waukesha Octane Test engine, which is found at every refinery but seldom elsewhere. Most octane numbers are estimated from the composition of the fuel.

I understand that gas stations are inspected and what not but is the fuel really what is advertised?

No they are not. The signage at the pump is totally meaningless and should be ignored.
Pump gas should never be used in an expensive performance engine. Pump gasolines are totally inconsistent and subject to constant change. The EPA requires changes in certain specifications on a monthly, state by state basis. But that is measured at the refinery, not at the pump.

how do I know that the fuel they use isn’t the problem? Has anyone tested fuel octane with a tester of some kind?

Recently I tested fuels for the Formula SAE program at Michigan and Nebraska. I tested three fuels from Sunoco: 260GT, E-85, and 93 octane pump gas. Comparing several years of data for the "same" fuels, I can assure everyone, they are never the same.

The largest variances were found with 93 octane pump gas. Both the SpG, stoich and alcohol content varied considerably, as did the di-electric values. Previous lab analysis has confirmed the extreme variances of the component composition as well.

E-85 could actually be anywhere from E-70 to E-87. And the alcohol is prone to water absorption.

The most consistent of the fuels tested was 260GT race fuel. It had a lower alcohol content with much more consistency regarding other variables.

I know what ever they used last winter in Tx for a winter blend hurts fuel economy by 2 to 3 mpg.

[427dart]

Do additives/octane boosters like "Race Gas" brand help with the pump gas issues?

[David Redszus]

Do additives/octane boosters like "Race Gas" brand help with the pump gas issues?

Power boosting additives typically focus on octane improvement and little else. While octane can be important in certain applications, it is not the only factor to consider. In fact, in many engines, octane is only a minor factor.

The selection of the proper fuel and correct engine tuning is just as important as proper
engine design, construction and assembly. Included in the long list of fuel variables
which must be considered are:

True octane requirement
Boiling point and distillation curve
Vapor pressure
Specific gravity
Stoichiometric ratio
Deposits
Preignition control
Heat of vaporization
Heat of combustion
Specific heat
Health & Safety
Legality

When a fuel is "off spec", any of the above factors could be responsible. A simple octane booster will not restore a fuel to its original properties.

[Roundybout]

For the street, tune for 87 octane and run 93/94 then hope for the best. I know a lot do but I'd never run a performance boosted application on the street unless running E85 and even then it's a crapshoot. I'm lucky enough to have a non-ethanol 93 octane around the corner that seems to be ok. (knock on wood)

[rustbucket79]

For the street, tune for 87 octane and run 93/94 then hope for the best. I know a lot do but I'd never run a performance boosted application on the street unless running E85 and even then it's a crapshoot. I'm lucky enough to have a non-ethanol 93 octane around the corner that seems to be ok. (knock on wood)

This. Tune with lesser octane, yet demand they run 93. Have them stay with one station, and it should be a busy station so they aren't buying stale fuel.

[swampbuggy]

What was the advertised octane of the premium level gasolines back in the 1960's up to 1970. Lets take the famed Sunoco 260, remember the dial on the pump ?? Mark H.

[MadBill]

Sunoco 260 was rated as high as 102 Research Octane, but that still had some low test blended in. Some stations reworked the blend pumps to dispense pure high test, designated 280. Rumors ran as high as 106 RON for it, but I think 104 was more likely. It ran completely knock-free in my 12.8:1 '70 Z-28.

[Roundybout]

Another thing to consider is there's no separate tanks (usually) of the different octanes advertised at the station. It's a large tank of lower octane fuel and a smaller tank of higher octane. To get 89 mid grade it's blended right at the pump from the two tanks. Who knows how accurate that is between different stations. Some higher altitude regions have 85 octane as the base and it's blended up to the higher octanes at the pump. What the cheap stuff is composed of or the higher octane for that matter and how long it's been there is anyone's guess. You'll often see when a station is out of 87 they only have higher octane available and vice versa with no mid grades. AV gas at least has more stringent quality controls because it's bad to have a plane fall out of the sky due to poor quality fuel. The only thing it has going for it is the octane though and isn't formulated for passenger cars. The list of differences other than just octane can be substantial.

[GARY C]

It's interesting that like all of these fuel discussions the best fuel ends up being the one with the better octane rating for the application even though the OP was trying to find info on actual pump gas. Is it possible that the better octane rating for an application is used because it is derived from the other components that we are told to look at?