Preferred Pump Gas (Not E85)

[BBO Omega]

Here in Virginia Beach we have the availability of 93oct E10 fuel from most every vendor. I typically default to Sunoco as I use the Sunoco 110 to mix (Sunoco states this is fine). That said, do you guys have an opinion on the best Pump Gas?

[F-BIRD'88]

Here it is PetroCan ULTRA 94 unleaded.
Formerly Sunoco... It has some ethanol in it.
Up to 10%.. May or may not now, soon be increasing that limit to 15%... Regulation standard changes, the fuel may not nessessarily change.

For when blending race gas we use PRO Racing Fuels Mark II 110 octane unleaded. (No ethanol in it) Here, it is highly illegal to run any amount of leaded gasoline in any street operated vehicle.
Track only, but most do not use a leaded gas for racing either.

[Roundybout]

I usually stick with the Shells, Sunoco and other top tier brands. I try to use a station with a lot of business and seem to be run well and clean. The only time I've ever had any problems with a tank of bad gas was the no-name stations and that's only been twice in my experience. We do have a few stations that offer ethanol free fuel in 93 octane. I use that in all my small engine stuff, dirt bikes ect. Ironic it's only the no-name places that offer the ethanol free stuff though.

[427dart]

Central Va. here and set mine engine up to run on various brands of 93 octane with the 427 Windsor comp. at 10.3

[dfarr67]

My experience with a DD truck- EFI tuned for high test, got into some remote area (poor fuel quality) when towing--> learned my lesson about tuning for the bleeding edge.

[David Redszus]

Last week I tested 11 drums of Sunoco 93 octane pump gas at MIS for a FSAE event.
It did not match refinery specs nor did it match last years fuel; same blend, same brand, same source.

For serious competition, NEVER run pump gas, regardless of brand. They are ALL very inconsistent.

Although race gas may well also be somewhat inconsistent, there is no comparison with regard to consistency.

[novadude]

David... that's interesting. What specific specs were "off" on the Sunoco 93 Pump Gas you inspected?

[BBO Omega]

As I don’t really drive my car a lot, I mostly mix in some 93oct Pump gas for the detergent. I learned is that the 110oct leaded gas can leave some extreme deposits in your Intake and Combustion Chambers. When I race, I always use straight Sunoco 110. Engine has 11.59cr (210psi Cranking Compression).

[David Redszus]

David... that's interesting. What specific specs were "off" on the Sunoco 93 Pump Gas you inspected?

Sunoco 93 pump gas showed inconsistencies in:
Specific Gravity
Stoich ratio
Alcohol content
Distillation curve
Heat of combustion
and high benzene levels.

Octane levels were not tested.

[MadBill]

Could the other variations (except for the benzene) all be explained by discrepant alcohol content, or must there have been several blending errors?

[David Redszus]

Could the other variations (except for the benzene) all be explained by discrepant alcohol content, or must there have been several blending errors?

Based on your prompt, i reviewed the differences in test results for Sunoco 93. While the variances from drum to drum were quite small, the difference between this years fuel supply and last years was substantial.

The current Sunoco 93 showed a reduced alcohol content (11% to 3%), yet the specific gravity increased substantially (.680 to .710). Since ethanol has a specific gravity of .794, you would expect the current fuel to show a reduced SpG as well.
In addition, the di-electric constant moved in the wrong direction based on reduced oxygenate.

Since pump gasolines typically consist of over 400 components, it would seem we are seeing a very much different fuel than last years blend. But these are not blending errors. The results are well within EPA and refinery specifications. Its just the nature of the beast.

[Truckedup]

The dyno shop I use tests only bikes and snowmobiles.. The shop owner commonly tests the RVP of customer supplied race fuel in cans opened the day of the dyno testing.. He claims many cans are "stale" and the RVP is not as advertised...

[novadude]

How much variance in the distillation curve is typical for pump gas? I would imagine this property can have significant effects on timing requirements, performance, and economy.

[David Redszus]

How much variance in the distillation curve is typical for pump gas? I would imagine this property can have significant effects on timing requirements, performance, and economy.

A difference in distillation curve indicates that the composition of the fuel has changed. A change in fuel composition will affect every fuel property.

Since most racers and tuners (and fuel merchants as well) do not have the means to test fuel, the best indicator regarding blend selection is distillation curve; followed by RVP, and then octane. But that is a starting point only; now we need to see what the engine likes (or not). The question of fuel consistency remains problematic.