91 w/o Ethanol, or 93 with 10%?

[200hp/tonne]

Originally Posted by StormTrooper

Yeah i've heard that before and had a pretty good idea of why......doesn't mean i couldn't get more power from a tune with better gas though.

My only consolation is that it's usually pretty cold which helps with air density and power.
kinda sucks to know that every turbo car or truck has an advantage regardless of rated power.

(Apologies for topic change) Sir, i am so sorry to report that a 25F difference in temperature results in only ~3% difference in ambient density, which would most likely be compensated for by the fact that hotter air flows easier (lower viscosity). Since ultimately the throttle plate controls air density into the engine, there are no benefits to colder air at part throttle.
Granted, i write without any knowledge of what your temperatures are compared to mine, but as a combustion engineer, the hysteria surrounding cold air and cold air intakes bugs me a little.

[Allch Chcar]

Originally Posted by 200hp/tonne

Ethanol has energy content of ~27 kj/g while gasoline is closer to ~45 kj/g.
So any E10 will have ~43 kj/g energy content. Day to day driving, where you stay below 70% throttle all the time, you will never be in the knock limited region of the spark timing map, so the 91 w/o ethanol will give you ~5 % better gas mileage. If you go WOT a lot of the time on 91 oct, then you will run into the knock region of the map (low speed high throttle, high speed high throttle) and the ECU will pull timing from MBT (max brake torque) timing and you will lose some torque. Here, 93 oct will be most beneficial. I try to keep no alcohol 93 oct in my tank all the time provided the price difference is not more than 10% compared to 93 E10.

You're using mass. Ethanol has a higher specific mass than Gasoline due to the presence of Oxygen. Ethanol has closer to 66%(65.75%) of the energy per gallon(volume) of Gasoline. Meaning E10 will have 96.7% of the energy of a gallon of Gasoline. The presence of oxygen also makes it perform differently since it will absorb heat from the air and cool the intake and combustion chamber as it evaporates. Far more than Gasoline can. Which is why E85 even though it's 95 AKI octane will perform vastly different than 95 AKI octane Gasoline.

http://www.afdc.energy.gov/fuels/fue...ison_chart.pdf

Originally Posted by A5D5TRYR

I'm going to switch back to 94 with 10% ethanol. With it getting warmer out it feels like I'm starting to lose a bit of power up in the rev range and given what I've read on these forums I wouldn't be surprised at all if it's starting to pull a bit of timing. I'd rather get mildly worse mileage but not be pulling any timing.

Higher octane should get better MPG if lower octane retards the timing. The timing advance at partial load actually plays an important role in fuel economy. That's why some manufacturers use premium in their fuel efficiency kings. Peak power and peak efficiency is less important unless you're racing. Higher octane can improve both.

[A5D5TRYR]

Originally Posted by Allch Chcar

Higher octane should get better MPG if lower octane retards the timing. The timing advance at partial load actually plays an important role in fuel economy. That's why some manufacturers use premium in their fuel efficiency kings. Peak power and peak efficiency is less important unless you're racing. Higher octane can improve both.

Keep in mind I'm in Ontario and my options are 91 pure gas or 94 E10. For the amount that I'm driving up in that rev range where it pulls timing (not that much) the better efficiency due to 94 doesn't make up for the better mileage of pure gas the rest of the time. I consistently see noticeably better mileage with 91 pure as opposed to 94 E10. But I don't like feeling the top drop off the way it does with 91 so that's why I'm switching back. You gotta pay to play and I like to play.

[Allch Chcar]

Originally Posted by A5D5TRYR

Keep in mind I'm in Ontario and my options are 91 pure gas or 94 E10. For the amount that I'm driving up in that rev range where it pulls timing (not that much) the better efficiency due to 94 doesn't make up for the better mileage of pure gas the rest of the time. I consistently see noticeably better mileage with 91 pure as opposed to 94 E10. But I don't like feeling the top drop off the way it does with 91 so that's why I'm switching back. You gotta pay to play and I like to play.

You should be able to feel a difference in the lower RPM response though.
How much more mileage and at what spreads?

[200hp/tonne]

@ Allch Chcar
Totally agree with you on E85.
E10 though, does not have the cooling benefit of E85, does not have high combustion speed of E85, does not have slightly higher specific gravity benefit of E85.
I used mass because fuel is sold by the gallon, but is used in our cars by mass, and all ecu calculations are mass based and not volume based.

We conducted few flex fuel studies in our research, and long story short, we matched results with the following paper,
http://www.sciencedirect.com/science...001005088#FIG3

Torque output does increase, but so does Brake specific fuel consumption, which affects MPG numbers the most. The torque numbers increased due to increase in octane number, but in our discussion we are dealing with commercially available fuels, which have equivalent octane numbers.

In conclusion, for the same octane number, E10 should have higher brake specific fuel consumption, i.e. Lower MPG. This was demonstrated by using 91 E10 and 91 Pure gas in a non flex fuel Chevy Malibu, at 70 mph on I85, 29 mpg on E10, 31.4 on E0.

The op should maybe try this same experiment, since i can't drive this car without a lead foot...

{edit}
Jut saw the posts posted while i was typing....glad to know fun took precedence over MPG.
Too bad the op does not have 93 pure gas, best of both worlds...

[A5D5TRYR]

Originally Posted by Allch Chcar

You should be able to feel a difference in the lower RPM response though.
How much more mileage and at what spreads?

I don't know that I feel much of a difference in the lower RPM but on my next tank when I switch I will try to see if I notice a difference. It may take a little while for it to learn back though right?
As for mileage difference I probably see about a 2 - 2.5 mpg difference between the two. However it's hard to say for sure as I don't drive the exact same way each tank and some have more or less highway driving but from what I can see that seems to be about the difference.

[Allch Chcar]

Originally Posted by 200hp/tonne

@ Allch Chcar
...In conclusion, for the same octane number, E10 should have higher brake specific fuel consumption, i.e. Lower MPG. This was demonstrated by using 91 E10 and 91 Pure gas in a non flex fuel Chevy Malibu, at 70 mph on I85, 29 mpg on E10, 31.4 on E0.

The op should maybe try this same experiment, since i can't drive this car without a lead foot...

{edit}
Jut saw the posts posted while i was typing....glad to know fun took precedence over MPG.
Too bad the op does not have 93 pure gas, best of both worlds...

What you're saying is correct. But at the same time, even though BSFC is 50% higher for Ethanol, MPG is "only" 30% less due to it having a higher specific mass than Gasoline. I've seem people confuse them before while looking at the different stoichiometric air to fuel ratios between E85 and Gasoline. I'm not an expert on the subject so I defer that I'm just trying to avoid confusion to anyone who might not be aware of the distinction.

What you saw for MPG seems to be abnormal though. I have heard of people losing far more MPG with E10 than is expected. But the studies I've seen have all shown a direct relation to BTU content. They just never followed it exactly. The improvement in octane peaks around E30-E40 but energy efficiency continued to improve the more Ethanol content there was. In fact power improves with more Ethanol content as well. Things like BSFC and fuel efficiency obviously decrease with Ethanol content. Pesky things that they are.

It's a fun subject and I enjoy learning more about it.

Originally Posted by A5D5TRYR

I don't know that I feel much of a difference in the lower RPM but on my next tank when I switch I will try to see if I notice a difference. It may take a little while for it to learn back though right?
As for mileage difference I probably see about a 2 - 2.5 mpg difference between the two. However it's hard to say for sure as I don't drive the exact same way each tank and some have more or less highway driving but from what I can see that seems to be about the difference.

It takes awhile, seems like at least 10-20 miles before the ECU makes any changes. According to what I've heard/read.

That's a big difference in MPG though. Some of it could be different situation and difference in driving style.

[A5D5TRYR]

Originally Posted by Allch Chcar

It takes awhile, seems like at least 10-20 miles before the ECU makes any changes. According to what I've heard/read.

That's a big difference in MPG though. Some of it could be different situation and difference in driving style.

I wasn't that surprised by it because I saw about the same difference with my last car (2010 WRX) over a lot more consistent driving. (>90% highway)