87 vs 89 E10

[Mach1Owner]

Hi guys.

Looking around online I have been seeing many people saying that when they run 89 in their 87 recommended car they are noticing 1.5-2 MPG better. Is there any basis for this? The only thing that I can think of would be that the knock sensor has to work less often.

I have also heard (may not be true) that 87 E10 is really 84 E0 with 10% E added, and that 89 E10 is 87 E0 with 10% E added, so the 89 E10 really has a better base fuel.

Any opinions? I do a LOT of driving for work, so even 1.5-2MPG would be enough for me to want to change, depending on the fuel costs at the time.

 

[volk06]

The first part, you will not notice much difference in gas mileage from 87 to 89. You will notice a difference if one of those is E0.

You are correct about 87 with ethanol actually being 84 octane plus ethanol to make 87 and the same with 89. The base fuel will have more energy content but not enough to make much of a noticeable difference on most vehicles.

Now depending on the vehicle, you will see 1.5-2mpg gain when going from E10 to E0

 

[bullwinkle]

Knock sensor can retard timing, hard to believe that would make a 1.5-2 MPG difference, though.

 

[Keith_Stone]

+1. To the OP, Eth is a good octane booster, but it's btu content is lower than good old fashioned E0 gas.

 

[oldhp]

Some gas plants make their base fuel 87 octane and still cut it with 10% ethanol, some don't. Kind of depends where fuel is going in the US.

 

[Artem]

My modified Scion tC with Toyota's 2.4L 2AZ-FE engine seems to run better on the good ol' butt dyno. Pulls harder and idles smoother. I did back to back testing over many, many takes, running 87 for a few tanks and then 89 from the same gas station.

I now stick with 89. Premium 93 octane (in my area) doesn't seem to give any benefit over 89, so I don't use it in my particular case.

 

[y_p_w]

I believe you are correct that the ethanol is indeed used to make a higher octane pump fuel. However, I'm not sure if your numbers are correct. Ethanol has an (R+M)/2 blending octane of about 99. The mixture of the fuel will be tailored such that the final blend with ethanol meets the pump rating.

My calculation is that 91 octane E10 would require a base gasoline with a blending octane of about 90.2. The spread might be a bit higher for 87 octane. I calculated about 85.7. Since the target octane is lower, the ability of ethanol to bring it up is higher. If you're trying to make a higher octane fuel, the ability of ethanol to improve the octane to your target number is reduced.

It's really a math exercise. Brush up on your algebra.

(99 + 9*base octane)/10 = target octane

Just plug in your target and it's:

base octane = ((target octane*10)-99)/9

 

[y_p_w]

Originally Posted By: oldhp
Some gas plants make their base fuel 87 octane and still cut it with 10% ethanol, some don't. Kind of depends where fuel is going in the US.

Unlikely in California. Gas is practically required to be oxygenated in most areas, and the blending octane of ethanol really helps with the final octane rating. There's a large demand for premium with tons of MBs, BMWs, and any number of performance cars.

I think MTBE was even a better octane booster, but it had other issues.

 

[KeithS_NW_Ohio]

Originally Posted By: Mach1Owner
Hi guys.
I have also heard (may not be true) that 87 E10 is really 84 E0 with 10% E added, and that 89 E10 is 87 E0 with 10% E added, so the 89 E10 really has a better base fuel.

Most single hose dispensers these days are blenders. They blend 66% 87 octane with 34% 93 octane to get 89 octane. Saves on one less underground tank.
10% E raises the octane 2 points.

 

[y_p_w]

Originally Posted By: KeithS_NW_Ohio
Originally Posted By: Mach1Owner
Hi guys.
I have also heard (may not be true) that 87 E10 is really 84 E0 with 10% E added, and that 89 E10 is 87 E0 with 10% E added, so the 89 E10 really has a better base fuel.

Most single hose dispensers these days are blenders. They blend 66% 87 octane with 34% 93 octane to get 89 octane. Saves on one less underground tank.
10% E raises the octane 2 points.

In California we've got typical 87 and 91. I've seen deliveries where the tanker connectors were clearly marked with the amount of fuel and the octane rating. None were 89. A few years ago I asked one driver if the fuel was blended, and he said one tank had three compartments and showed me the seam and said that a small part of his load was 89 octane in his smallest compartment.

There is one place around here that sells 100 octane racing gas. The pumps have a separate hose for 87 and one for 94/96/98/100. I suspect they blend the 100 octane with 91 to arrive at the final blending octane.

 

[NMBurb02]

Originally Posted By: y_p_w

Those stickers are rather low budget for such expensive gas. $6/gallon for 96 and he has to cut out a 9, flip it over and glue it on top of another number? $7/gallon for 98 and he flips over an 86 (does anyone even sell 86 octane gas?)? Don't let me get started on the 100 octane sticker...it looks like the station owner moonlights as a ransom note writer! That alone would turn me off from buying there. Have at least a little pride in your station, spend a few bucks, and get some custom stickers made!

 

[y_p_w]

Originally Posted By: NMBurb02
Originally Posted By: y_p_w

Those stickers are rather low budget for such expensive gas. $6/gallon for 96 and he has to cut out a 9, flip it over and glue it on top of another number? $7/gallon for 98 and he flips over an 86 (does anyone even sell 86 octane gas?)? Don't let me get started on the 100 octane sticker...it looks like the station owner moonlights as a ransom note writer! That alone would turn me off from buying there. Have at least a little pride in your station, spend a few bucks, and get some custom stickers made!

For some people, the low rent look of the pump is part of the charm. That's possibly the cheapest gas in the area for 87/89/91. It's an independent and the station otherwise looks impeccably maintained. That photo was taken a while back when the prices were near their high.

It's one of the few stations with race fuel or at least 93/94. It's in the middle of nowhere on I-680 - maybe 5 miles in each direction from the next closest gas station. If you've got an STi, Evo, Porsche, GT-R, etc this is one of the better options. A lot of the extreme tuner mods with the ill fitting ground effects and the bare metal spoilers filling up on race gas fit right in with the makeshift look of those buttons.

 

[Mach1Owner]

My mustang was tuned on 94, sucked that a few months later all I could find was 91.

 

[y_p_w]

Originally Posted By: Mach1Owner
My mustang was tuned on 94, sucked that a few months later all I could find was 91.

I'm guessing you were finding real 94 and not 100 octane race gas blended to get 94. Race fuel is super pricey, but it's the only practical way to get a CARB legal 93+ here.

I was in PA earlier this year - in a suburb around Philly. I remember signs at Sunoco and some Chevron stations that they had 94 octane.

 

[Mach1Owner]

I'd like to know where. I'm in a philly burb and I cant find 94 ANY place. i know of only 1 place that carries 100.

 

[y_p_w]

Originally Posted By: Mach1Owner
I'd like to know where. I'm in a philly burb and I cant find 94 ANY place. i know of only 1 place that carries 100.

We were visiting friends in Chester Springs, but we were driven around in Paoli, Exton, and Malvern. It might not have been 94 but 93. When I was in FL it was 94.

I found a street view on Google Maps of a station in West Chester with a clear shot of a sign with "Ultra 93". Perhaps it wasn't 94. You wanted higher than 93?

http://maps.google.com/maps?q=exton+pa+s...1,4.33&z=19

 

[Mach1Owner]

My car was dyno tuned on 94, so I get it when I find it. The fuel economy on 91/92 is noticeably worse than 93 is and 94 was just fine.

 

[y_p_w]

Originally Posted By: Mach1Owner
My car was dyno tuned on 94, so I get it when I find it. The fuel economy on 91/92 is noticeably worse than 93 is and 94 was just fine.

Understood. Actually I'm not sure if 94 was really all that common even when I was down in FL. It might have been just one station where I saw it that had it. Also - I heard a lot of places switched to a 93 octane equivalent when they started phasing out MTBE. It has a blending octane of about 103, and could be used up to 15%. It was cheaper than ethanol and has less of the performance drawbacks such as attracting water. But the health effects of the vapor are what killed its use.

 

[TiredTrucker]

But ethanol only attracts any water in the fuel tank or that condenses in there. Is that such a bad thing? Getting the water out of the fuel? It isn't like ethanol is posting a sign on the side of the vehicle, inviting water to the party.

Man, if ethanol attracts water so badly from everywhere, I must be running on a lot of water by using E85.

 

[SHOZ]

The problem with it attracting water is once it has absorbed so much then it separates from the gasoline and just sits there at the low spot. No amount of extra alcohol will make it mix up again.