I was hoping that I could get some more experienced members to chime in on running these cars on E85 and also advancing the timing.

I am running +2 degrees timing on the E85, which is a minimum of 100 octane. I am also at about 5,000 feet altitude. Do you think this is safe? I have noticed no engine knock.

 

Dont knock sensors kick in to retard timing to eliminate knock before you could notice it? Unless your ECU control that has advanced the timing is over riding the ability of the ECU to retard the timing.

 

advancing the timing won't stop the ecu from detecting the knock and retarding it.

not sure if ur specs are safe tho.

 

Ah, thank you.

 

https://g35driver.com/forums/4109232-post130.html

 

from what i gather, e85 is a total political joke in this country. it is being touted as cheaper, great for the environment as cleaner, renewable energy, but in reality:

corn is diverted from the food supply to make ethanol which has resulted in the highest per bushel price of corn in history; only few cars have the fuel system to handle the water that comes along with this much ethanol; and the worst is that the energy density of ethanol is so much lower then gasoline that the negligable difference in price between e85 and regular octane gas is completely reversed by having to use more gallons of e85.

i wouldn't run it unless i had to.

amp

 

All political stuff aside ...

I get the exact same mileage running E85 as I did premium. All city driving, excessive A/C use, and I get exactly 15 every single time based off of the car's computer and my logbook.

Since E85 here is $1.99 and premium is about $2.89, I'm saving a lot of money.

To anybody thinking of trying E85 in their G35, I would recommend adding in a little Marvel Mystery Oil (or similar fuel system lubricant) to make up for E85 not being as lubricating as gasoline.

 

i find that very interesting! i'm not saying you aren't right as you probably keep very good records. it does fly in the face of logic however:

As ethanol content in gasoline increases mileage declines in line with the fact that ethanol has only 67% of the energy of gasoline.

A study was done by the DOE. To quote from the study (page xvii):

"All 13 vehicles exhibited a loss in fuel economy commensurate with the energy density of the fuel. With E20, the average reduction in fuel economy (i.e., the reduction in miles per gallon) was 7.7 percent compared to E0. Limited evaluations of fuel with as much as 30% ethanol were conducted, and the reduction in miles per gallon continued as a linear trend with increasing ethanol content."

And on page 3-3:


"Changes in fuel economy were consistent based on fuel type and the change in energy density of the ethanol blends—approximately a 4% decrease in energy for every 10% of ethanol in the fuel."


following that line of reasoning, if premium fuel costs 2.89, then e85 should run about 2.04 for equivalent energy density. at 1.99, you are saving .05 per gallon or less than the price difference between premium and midgrade.

theoretically...

not sure why your mileage would stay the same on e85? maybe there is something about the engine that it somehow likes the e85 better?

amp

 

Remember that E85 is 100-105 octane. Our engines have compression ratios of 10.9:1.

Even though E85 contains less BTU's than gasoline per volume, roughly 20%, the engine's high compression takes advantage of the higher octane, making it run more efficiently.

This is my explanation.

 

that is a good theory. i liked it when i initially read it, but after digging a bit, i think it may not be possible unless there was a way to significantly raise the compression ratio (up near 16:1 from 10.9:1) to fully take advantage of the higher octane rating.

it looks like to get the same power from running e85 as compared to gasoline, it might also be necessary to run upgraded injectors that can handle the 20% extra fuel needed to fill the cylinders with the higher compression ratios. the compression ratio gives you an efficiency boost, the larger volume brings your btu processing back in line due to the inherent lower energy density of ethanol.

if you ran the mass and energy balance, you could prove there is no way to get something for nothing. you can increase the efficiency of the combustion process by raising the compression ratio, but you're still limited by the btu/gallon of the ethanol. i don't think you could get the 33% increase in efficiency it would take to overcome the 67% energy density deficit of ethanol as compared to gasoline.

here's a wiki article that uses similar numbers from other internet references i found.



Depending on composition and source, E85 has an octane rating of 100–105 compared to regular gasoline's typical rating of 85–93. This allows it to be used in higher compression engines which tend to produce more power per unit of displacement than their gasoline counterparts. Since the reciprocating mass of the engine increases in proportion to the displacement of the engine E85 has a higher potential (potential is the key word here) efficiency for an engine of equal power.

One complication is that use of gasoline in an engine with a high enough compression ratio to use E85 efficiently would likely result in catastrophic failure due to engine detonation, as the octane rating of gasoline is not high enough to withstand the greater compression ratios in use in an engine specifically designed to run on E85. Use of E85 in an engine designed specifically for gasoline would result in a loss of the potential efficiency that it is possible to gain with this fuel. Using E85 in a gasoline engine has the drawback of achieving lower fuel economy as more fuel is needed per unit air (stoichiometric fuel ratio) to run the engine in comparison with gasoline. This corresponds to a lower heating value (units of energy per unit mass) for E85 than gasoline.

E85 consumes more fuel in flex fuel type vehicles when the vehicle uses the same compression for both E85 and gasoline because of its lower stoichiometric fuel ratio and lower heating value. European car maker Saab currently produces a flex fuel version of their 9-5 sedan which consumes the same amount of fuel whether running e85 or gasoline,[13] though it is not available in the United States. So in order to save money at the pump with current flex fuel vehicles available in the United States the price of E85 must be much lower than gasoline. Currently E85 is about 5-10% less expensive in most areas.



sorry, i know that isn't helping us get to the bottom of this very fast, but at least it's fun to learn about how this stuff really works.

amp

 

to get back to your original question, my instinct after seeing the numbers is that you are safe running your engine the way you are.

if you wanted to be sure, you could find a shop with a portable scan tool and operate the car the way you normally do and see if the ecu is detecting any knock and changing the timing curve. my guess is that it is not.

amp

 

You're definitely right that 10.9:1 isn't enough to take full advantage of E85's compression ratio. I know people with WRX's that get better mileage on E85 thanks to being turbocharged.

You're also right that to make the same amount of power, one would need larger injectors. But remember that E85 has a cooling effect when it burns. I have solid accelerometer 1/4 mile runs showing that I've lost 0 horsepower running on E85.

 

you can talk theory all day long. and believe me, I am all about theory.

but the numbers dont lie. this is interesting stuff!

 

I don't think running 100% E85 on a system designed for gas is a great idea. Isn't E85 corrosive to the oem rubber fuel lines?

 

yes, i read there is a cooling effect. i wonder how much compared to gas?

and isn't it the increased moles of 02 per liter of air in cool air that improves power? seems like that would have to occur before the MAF, not in the cylinder where the injectors put the ethanol. it doesn't seem like there would be time for it to cool the intake air very much to get more o2 into the cylinder to really improve things much.

but as posted, the numbers don't seem to coincide with the theory.

amp