Joe_G

I just noticed a gas station at the edge of the everglades sells pure gasoline (no ethanol) but the octane is only 90.

Since gasoline has more btu's per oz than ethanol, I wonder if this pure gas would produce more power than E10 with a 93 octane rating?

It has an unleaded nozzle and is $4.10/gal, .20 more than 93 octane but a lot less than Sunoco 103 at $10/gal

Anyone know?

BAKnBLK2010

The simple answer is no. 93 octane rated fuel with or without ethanol will in fact have a greater anti knock rating than a 90 octane rated fuel with or without ethanol....

Joe_G

Yes, but a higher knock resistance doesn't matter if the engine doesn't need the higher octane. There is no need for me to put Sunoco 103 in my car for cruising around town, in fact, I suspect the slower burn rate might hurt mileage.

If the engine wouldn't knock on 90 octane I suspect fuel mileage and power output would be higher given the higher BTU content of pure gasoline.

In my case, I have 11.8/1 compression so would have to knock down timing too much at WOT to use it, but I suspect I could leave part throttle timing alone and get slightly better mileage.

I wonder if the better mileage would offset the $.20 higher per gallon price.

mikeCsix

I found an 8 - 10% difference in mileage between E-10 and pure gasoline.

I'd be a bit leery of buying gasoline for my very expensive sports car from the vendor depicted in the above ground tank. Enthol? I think he/she meant ethanol.

saplumr

What you gain with ethanol free is longer shelf life and better fuel mileage. I would asume the extra expense would cancel out any fuel savings. I can only assume the power diff between 90 octane 100% free and 93 ethanol octane will be a wash.

Joe_G

Yea it's the Seminole Truck Stop and Tiki Bar out at the edge of civilization...it's a biker bar as highway 27 is a good bike riding road, very little traffic unlike most of our roads here.

Here was my favorite scoot from today's show...must have been 300 bikes there. Talk about getting back into the saddle....

BAKnBLK2010

Adding 10% ethanol to gasoline actually increases the octane rating. The base stock for 87 octane gas with ethanol is actually 84 octane gasoline. When you add in the 10% ethanol the 84 octane base stock then becomes 87 octane gasoline. The base stock for premium 93 octane is actually 90 octane and when you add in the 10% ethanol it becomes 93 octane. The 90 octane that the OP has access to is sold for boaters that have carbureted motors on their boats. Everyone hates on ethanol but in reality it is a great anti knock agent. E85 has proven to be an outstanding fuel for supercharged and turbo motors. The one downside to ethanol based fuels is they draw a lot of moisture and don't store well. That is why boaters have a need for non ethanol fuel as they tend to not run out a tank of fuel as fast as we do in our cars.

Slick6

Octane ratings have no correlation to power produced. Octane prevents detonation and higher octane fuel is recommended for vehicles that are more aggressively timed, which is why a turbo 4-banger usually needs 93 octane while the NA version of the same motor only needs regular 87 octane gas. Yes, high performance cars like ours produce a lot of power, but the octane rating is for the timing curve, not to produce the power itself.

dicky

Joe, I tried this several months back and I didn't have any luck. I have a station close to my house in Louisiana that sells 87 pure gas so I got that and added octane booster. My 1st run with this gave me a bunch of knock so I dropped my timing down just a tad made a knock free run and still a slower than normal run (11.44 I think vs low 11s).

dicky

njedwardz

long story short is that if your car is tuned for 90 or 91 or 87 or 60 or whatever, running 93 or 115 or jet fuel (kidding) isn't going to give you any more power or performance. A car tuned for 93 running 93 will (should) be xx% faster than a car tuned for 87 running 87, 93, race fuel, etc.

What would be sweet is an average octane (and fuel composition) sensor in the fuel tank that dynamically adjusts your timing and fuel curves to give you the best AFR and maximum possible performance for a given tank of fuel!

SgtB10

Isn't that what the Flex Fuel trucks do? My Tahoe will run on 87 or straight E85. I don't have to do anything but fill it up with either and hit the gas pedal.

I guess I'm the odd man out on octane and tuning. I have my vehicles dyno tuned on 89 octane and then only run 91 to 93 (depending on what's available where I am) to be extra safe in case I get a crappy tank of fuel from a place like in then OPs picture lol...

njedwardz

Not SUPER familiar with the flex fuel system, but Wikipedia suggests that they have a fuel composition sensor. It appears I stand corrected haha! I'm not sure as to the existence of a legitimate octane sensor (besides a knock sensor, which I don't count at all)

SG4206

Joe , I'm with you on this. I think the specific gravity of the 90 straight gas might higher than the diluted at 93. If so, it will make more power.

Maybe a chemical engineer can answer.

Joe_G

Hey Dicky! How are you buddy...haven't seen you in a whole, hope we run into each other one of these days.

Did you notice any increase in fuel mileage? If I could get 10% higher fuel mileage as mikeCsix found, that would be useful for me. I coukd always pop in a gallon of race fuel at the track.

Joe_G

I think it will too...but I cannot find an article to support it, I know I must have read something on it as I didn't dream it up...

Would be good to hear from a chemical engineer indeed.

glenB

Have you adjusted the A/F in the tune to run the E10 ?

Joe_G

Yes I have. But a factory tune can handle it it as it seeks lamda via the o2's. A factory tune cannot handle e85 unless it has the fuel sensor and the tables completed in the tune and enough headroom in the injectors and fuel pump. Most GM cars have the tables but not the sensor, but guys can retrofit the sensor. Dsteck did a big thread on how to do it with a modded sensor, I think Lingenfelder now sells them for retrofit.

Seems I did read about a guy who ran e85 without a sensor or tune...but I don't recall how that ended up long term.

As I think more about this, I am quite certain fuel mileage will improve slightly with pure gasoline vs e10. Fuel mileage is substantially lower with e85 due to lower btu's and more fuel needed so the inverse must be true.

I don't think the difference would be 10% however.

icntdrv55

The old "higher octane fuel will give me more HP" myth always was--and still is--incorrect. Higher octane reduces pre-combustion (slows flame-front travel) in high compression engines. You can certainly BUILD a high compression-ratio (CR) engine to USE the higher octane fuels, and it will indeed make more HP than an engine with lower CR built to run on lower octane fuel. Your Vette was built and tuned to use 91 octane, so feeding it 93 won't make it any more powerful. If you feed it the 90 and experience knock, then the ECU will retard timing slightly, which MAY lower HP slightly. Your butt dynamometer won't be able to tell the difference.

As has been stated previously, the EtOH fuel doesn't age as well as straight gasoline. Water inclusion is the main issue, although with our plastic tanks, rust isn't one of the negatives. In my part of the world, it's almost impossible to find 100% gas unless you visit a marina and pay the unconscionable price they want, so I always use a fuel stabilizer when I put my car away for the winter.

icntdrv55

Hey, I'm not a ChemE, but I have Google-Fu!
The specific gravity of EtOH USP is approx 0.814; the specific gravity of gasoline is approx 0.739. [BTW, the SG of 87 vs 91 octane is essentially the same.] A 10% blend of ethanol in gas will increase the SG but not appreciably. I'd bet a paltry sum of cash that the flex fuel vehicles adjust the timing curve for various fuel blends based on the knock sensor and NOT by measuring the SG of the current fuel load. But hey, that's a WAG….

MyLS1Hauls

The current Flex Fuel vehicles have a "virtual" sensor...meaning that there is no physical sensor in the fuel line. The composition of the fuel is not "measured", but "calculated". When the PCM sees a large change in fuel level, it watches the O2 sensors for changes in A/F ratio, which correspond with a change in fuel composition. It then calculates the ethanol percentage, based on A/F ratio corrections required, and applies the timing curves that correspond with that content. There are complicated algorithms involved, but those are the basics of how it is done. The LT1 based trucks have a physical sensor, as it is possible to slightly confuse the "virtual" sensor, if you only partially fill up, or fill up before very much fuel is used. Early flex fuel vehicles also used a physical sensor.

As for what fuel to use...I'd use 93 E10 from a busy station over 90 E0 from some small station in the middle of BFE. 93 octane E10 will allow more timing advance, and will therefore make more power, in an 11.8:1 motor. Because the BTU content of E10 is lower than E0, your fuel economy will be slightly lower. There is nothing wrong with ethanol blended fuel, when it is stored properly and used within a few months. I've used it in my 2 stroke snowmobiles, jet skis, outboards, and every other piece of power equipment, without issue. The slight loss in fuel economy has been my only gripe. It will varnish and gum up faster than straight gasoline, but just don't leave it sitting unused for an extended period of time.