Thread: E85 fuel FAQ
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Old 07-08-2005, 11:54 PM   #3
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Join Date: Jan 2002
Location: [email protected] @ 5800 ft on 13T
2002 Impreza WRX


Part 3

Testing ethanol content with the water test
The proper way to do the water test is specified on page 27 of the handbook.

Handbook method:


2.1 + 1.94 x (total vol - lower meniscus) = hydrocarbon
ethanol = 100 - hydrocarbon

Ethanol bonds very strongly with water so the percentage is not a direct relationship as seen above in the formula.
For example, If you add 10 ml of water to 100 ml of standard pump gasoline, and end up with 17ml of phase separation -- you have a full E10. (yes I know the math does not work but this is due to ethanol's bonding properties) In this case 10 ml of water and 10 ml of alcohol bond to form a mixture of 17 ml of water alcohol mix.

Choosing proper injector size for Subaru WRX E85 conversions

Simplified formula:

(turbo max air flow CFM at target boost) x 1.38 ~= static injector flow cc/min each injector on E85

(assumes a 4 cylinder engine with similar fuel needs to the Subaru WRX)

What is your test history to date (6/2005) with E85 ?

I just tallied up my usage over the last 2 years, (the first year I was very cautious and did not use very much). I've put about 500 gallons of E85 and 100% fuel grade ethanol through the cars tank --- that's some where around 40 fill ups, or around 9,000 miles or so on high ethanol (ie greater than 10%) blend fuels.

I am intentionally running the E85 with no special fuel system modifications. In a few years or when ever problems crop up, I'll pull things apart and see what has happened. So far I have absolutely no evidence of ANY kind of degradation on my 2002 WRX. The only non-stock component I'm running in the fuel system at the current time is a walbro 255 L/hr pump, so I cannot absolutely tell you how the stock pump likes the stuff.

Update ( Jan-Nov 2007)
I made a full conversion over the winter bringing the car back on the road with decapitated OEM injectors flow tested at 810 cc/min, an Aeromotive adjustable fuel pressure regulator which gives me the ability to dial in any fuel pressure I want from 35 psi to 70 psi with the turn of an allen wrench. A slightly improved ECUtek reflash, and the Mistubishi 16G turbo off a 96 Australian WRX. At 17 psi I produce 281 AWHP compared to 240 AWHP I was hitting on 100 octane Sunoco GT100 and 250 AWHP I could hit on Sunoco GT+ 104 octane race gasoline at higher boost pressures.

I have successfully tuned a usable home made FFV setup by optimizing the tune for a 50/50 blend of E85 and gasoline. At moderate boost levels the ECU is capable of making the necessary adjustments and open loop fueling is acceptable (see detail notes in the FFV segment below).

I have currently moved to a 100% E85 tune since I now have adequate availability of E85 and can run it all the time with little difficulty. In a cost per mile basis my current tune is equivalent to getting 30.5 mpg on pump premium (20 mpg on E85 at $2.19 vs pump premium at $3.35/gallon). On a cost basis the car is consistently cheaper to drive on E85 than it is on gasoline.

Why is E85 a better fuel ?

Ethanol and is a very turbo friendly fuel for many reasons.
1. It has a much higher evaporative cooling power than gasoline so the intake air charge in the cylinder is significantly cooler that it is with a comparable mixture of gasoline --- that means higher VE.

2. Its octane as blended in E85 is about 100, its blending octane when added to gasoline is rated at 118, so it is a very cost effective octane booster.

3. Ethanol burns faster than gasoline but has a slightly longer ignition delay during the slow burn phase of combustion so the engine does not do as much negative work fighting rising cylinder pressures due to large ignition advances. The total ignition advance for E85 is almost identical to the ideal advance for gasoline so it does not cause the ECU problems when you mix them.

4. At proper mixture you actually are releasing more energy in the cylinder due to the higher quantity of fuel you can burn. ( Ethanol can burn effeciently at much richer mixtures than gasoline can) That means about a 5% increase in energy release all by itself.

5. Peak combustion pressures are actually lower for ethanol than for gasoline but the cylinder pressures stay higher longer, so you have more (longer) crank angle that is usable by the engine. This lower peak cylinder pressure also helps with detonaton control.

6. It will, at proper mixtures lower EGT's by around 200 deg F, but due to the higher quantity of exhaust gas products it produces you do not lose any spool up (in fact I would wager spool up is better).

7. It is much cheaper ( if you go to a station that is not trying to price gouge).

How much will my miles per gallon of fuel drop with E85?

The only negative to E85 is that it gives a lower fuel milage on a gallon for gallon basis to gasoline. The actual difference in energy content between straight gasoline and E85 is about 27%.

The drop in mileage is not as significant as you would think based on that difference due to the higher efficiency of the ethanol as a high performance fuel. This winter I was getting about 92% of the fuel milage I would get on gasoline on 100% E85.

The lower mileage is not really a big deal, ethanol has lower energy per gallon but your reduction in milage is not nearly as large as that difference would imply. Due to the higher torque,you use slightly smaller throttle openings to get the same level of performance, and due to the greater quantity of combustion products (more moles of gas) per lb of fuel the engine efficiency actually goes up slightly. My long term fuel mileage average is in the vicinity of 24.5 mpg, with pump gas, and with 75% ethanol blend, I was getting just over 23 mpg driven normally. Recently I have been flogging the crap out of the car to sort out new boost controller settings for my new turbo (went from a 13T to a 16G). Given I now have a larger turbo and all that is hardly a noticeable fuel mileage drop. I have gotten around 300 -345 miles/tank on straight gasoline when I was bone stock, and I expect to get from 280 - 310 miles per tank on the E-85 based on my notes of fuel consumption and accounting for the unusually hard driving I have been doing the last week working on the boost controller settings.

In very cold weather <20deg F I don't go above about 90% E85 to improve cold starting and speed up engine warm up a bit. Other than that the car loves E85 and so does my wallet ---- $1.89/gallon (6/2005) for 100 octane fuel is hard to argue with. It only drops my fuel mileage a small amount. I get 93.76% of my gasoline milage when driving conservatively in my WRX with the larger injectors and high ethanol fuel blends.

will a wide band O2 sensor accurately read fuel air mixtures with E85 blends ?

To get an accurate AFR reading you need to switch the meter to Lambda or equivalence ratio setting rather than AFR. Most O2 sensors assume you are running gasoline and will report a stoichiometric mixture as 14.7:1 which is the proper value for gasoline. E85 has a Stoichiometric mixture of between 9.7 - 10:1 and a max power mixture of about 6.98-8.5:1 or so, where with gasoline it is 12.5:1-to 13.1.

If you must use an O2 sensor that only reports gasoline AFR information simply divide the numbers it reports by 1.47 - 1.50.

On gasoline, my ECU is supposed to give a mixture of 11.5:1 and on 100% E85 the dyno's wide band reported an AFR of 11.6:1. That means that my true AFR on the E85 was about 7.8:1 which is right in the middle of max power mixtures for E85.

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Last edited by hotrod; 04-02-2011 at 12:48 AM.
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