I understand that the 87-octane fuel sold in my area (Texas) is E-10. I assume they start with 85-octane regular and the 10% ethanol gets it to 87.
There is also a station near me that sells 88-octane E-15. I assume it's the same 85-octane regular and 15% ethanol. It's a few cents cheaper than the 87.
There are also stations near me that sell E-85, which is "minimum 70% ethanol". I don't know the octane of this fuel but I suspect it's over 100.

The performance benefits of running E-85 are well-documented. I can feel the difference in my bone-stock 2018 5.0. The problem is that E-85 costs only about 20% less than premium so on a cost-per-mile basis it's a pretty much a wash between the two.

So the cheap bastard in me thinks to myself... if I only need 93 octane to get peak performance out of this engine, what percentage of ethanol would I need to add to the 87-octane "regular" fuel to achieve this? If each 5% ethanol raises octane by about 1 point (which seems to be the case) then I would need E-40 to achieve 93 octane fuel. I can get that by filling my truck with about 15 gallons of E-85 and then filling it the rest of the way up with 87-octane regular. Voila, 93 octane for less than the price of regular. Right? Saves me nearly $20/tank vs. buying premium which is well worth the 60 seconds it takes me to switch pumps and swipe my credit card a second time. I lost about 1.5 mpg by doing this, which takes back some of the savings but I'm still way ahead.

Anyone see an issue with doing this? Is there any reason that my truck won't run at least as well on E-40 as straight 93-octane premium (which I assume is actually 91 octane with 10% ethanol)?

-David

 

lol

 

Boy you must have a lot of free time on your hands. I can't answer your questions and I question your premise but I can give some input from what I know. I spent quite a few years working at Sunoco's NE refining complex, later PES. A good bit of it in blending and shipping. RBOB gas ( Reformulated Gasoline Blendstock for Oxygen Blending) as traded on the futures market is blended and tested to an 85 octane rating which from what I learned is the average of the RON and MON. Ethanol is added at the distribution terminal along with other additives specific to gasoline marketer. Sunoco vs. BP vs. Exxon vs. Weasel **** are all the same gasoline from the refinery unless and this where the mystery begins, custom blends are specified. Ethanol was introduced to oxygenate the fuel replacing MTBE, poiltics and environmental concerns aside. The 10% you see listed at the pump is the max percentage it can contain and be compliant with the fuel standard. There are other things that could be added such as detergents or butane. Butane can be added from October to April up to 10% in volume to increase RVP. It also is added at the distribution terminal. It maintains vapor pressure, burns faster and costs less than gasoline. You see where this is going? It behooves the marketer to mix lower cost additives to the blend (ethanol, butane) and sell it at market rate. You noticed that milage decreases when you increase ethanol (many state the same with winter blended gasoline) that is because the BTU/volume is considerably less than gasoline so more is needed to get the same energy output. My personal experience is staying with Top Tier gasoline gets the most consistent results. I give you an A+ for effort but without lab analysis you are guessing at best. But you seem to be having fun doing it!

 

Here's a tool I used for blending. http://www.georgebelton.com/E85Calculator.php

 

Also, if you have a Bluetooth obd adapter, you can use the torque pro app to monitor your actual ethanol percentage.

 

I don't have the torque app, but I do have a different one. I get zero reading on E %. What is the trick?

 

Only Flex Fuel engines have the ethanol sensor, so all the EB and non flex 5.0 guys are screwed unless you go aftermarket.

 

Heard biggest issue around is that some stations, especially some run by a certain group of people put water in the underground tank.
Now Abu does have the cheapest gas, so something has to give. Don't know what situation a person drives where octane matters but
just guessing on mine where the truck hardly goes over 40, just stop sign to stop sign, not an issue. Just try stay with high volume,
top brands. If one has dumped some water in there, and my truck sits for a week without being driven, which is the norm. Gonna
have more concerns that how much power receive from the once a month or longer fill.

 

As stated, it only works on the flex fuel vehicle, which the OP has. For me, one of the gauges available in the torque pro app is for ethanol % and I have seen the percentage change when mixing e85 with regular e10 fuel in the tank. I don't know how accurate it is, but I would guess Ford has the ability to have a sensor that is very accurate.

 

WOW - so to add onto to another member aboves post.

1) adding ethanol doesn't raise the octane rating of the fuel. Yes I know internets and people running e85 swear by it's anti-knock and anti-retard properties and running oodles of timing and. It's not OCTANE however. It just burns cooler. See Octane rating is about the amount of OCTANE molecule in the unit of gasoline. Octane is the good stuff in basic terms. Adding ethanol does nothing for this infact it is watering down your gasoline. That 87 octane you buy that has 10% ethanol in it - starts off as 87 octane pure gas and they put in 10% by volume of Ethanol. And you hope - no water.

2) the company selling that 88 octane stuff is mostly a marketing gimmick they are lightly adding some octane to normal 87 fuel mix - so as to test as 88.

3) 93 octane rated gas that is e10 is again 93 octane pure gas that's been mixed with 10% by volume of ethanol. E85 is 87 octane base gas, that is 85% ethanol by volume the reason it doesn't have a standard octane rating is that it mostly ethanol and octane rating method doesn't apply.

Your engine with stock tuning will run it's best on 93 octane pure gasoline. The power spec ratings for them were all done with 93 octane pure gasoline. YOu can however retune the vehicle to run on e85. You can run pretty well on e85 and you can get high power out of it with major tuning changes. HOwever, you will use significantly more fuel per mile running e85 so don't think this will save you fuel money.

Hopefully this helps weed out some of the details. If you want to run e85 there are some good tunes for it