Optimum Fuel Selection

Sometimes when I go to bed, my brain does not want to shut off, and I start thinking about tasks that need to get done at work. I don’t like thinking about work when I’m trying to go to sleep, so instead I redirect my thinking to derby theories. There is endless possibilities for experiments and optimization in engines, transmissions, different make and model cars to build, and for different rules. The roadblock to trying new things, however, is often funnily enough, success. Why should you have any motivation to try something different if you are consistently doing well at each competition. But when you get knocked down a peg or two, if you are not a bullheaded ignoramus, you ought to reconsider the status quo and take a look around to see where you can improve.

Fuel selection has played a limited role in my family’s derby success. A number of times an engine getting hot has been the failure point for us, (as well as many, many others) and fuel is one parameter that can have an effect on engine temperature/longevity. In recent years, our usual policy has been to run 91 octane ethanol free pump gas whenever possible. I generally have to travel 1 hour round trip out of my way to get to the nearest station that supplies it though, so in a pinch I’ll also do 87 ethanol free, or even e10 pump gas (last resort), and perhaps a VP octane booster if the engine warrants it.

What got me pondering the status quo, though, was a presentation I saw on youtube about the benefits of running methanol fuel by Jason Koch. Now in my area, I don’t see methanol as viable. Most of the shows we run have a fuel tank size listed in the rules, 6 gallons for bone stock and 10 gallons for modified. In this case, running methanol, which requires twice as much fuel, would almost guarantee running out of fuel versus stiff competition. It did get my gears turning though, so I looked back to possibility of e85, and still came back that it was not ideal, as e85 takes specially modified carburetors which are not cheap, along with the same problem of requiring 30-35% more fuel. I found out while researching fuels an additional reason to avoid e10 as well. e10 has a higher vapor pressure than gasoline alone, and a lower boiling point, which means that it is more likely to boil and vapor lock on a hot engine.

I was excited to learn though, that the vapor pressure effect is not linear, and that as the ethanol concentration is increased, the RVP returns to the level of gasoline at about 50%. That got me thinking, what if I blended my own e40 fuel mix to get half of the benefits of e85 with minimal expenses. My plan is to jet up an Autolite 2100 carb I rebuilt and am running on an 87 Ford 5.0 that came out of a grand marquis (factory roller non H.O. motor). This is for a bonestock class pre-ran car that I seem to struggle keeping a radiator in. I am in short supply of copper/brass tank Ford radiators, so I broke down and purchased an aluminum one from Dillon Radiator. I detest plastic tank radiators for demo derby and you should too! I’ve overheated this motor 3 or 4 times now between 2 different cars, so I’m due to try and make an improvement. I figure that e85 takes 30% more fuel, so e40 should take 15% more fuel. This is closer to the factory calibrations on the carburetor so I am hoping that I can get away with a jet change to get in the right Air/Fuel Ratio.

AFR table for ethanol blends

Stoichiometric AFR for e40 comes to 12.42 by my calculations, with max power estimated at .85 lamda close to 10.6 :1 AFR. *Important to note that is true AFR, gasoline referenced AFR will still show AFR as 12.5

To gear up for this endeavor, I made some purchases to not be blindly guessing at the jetting. First was an Innovate LC-2 controller, 02 sensor, and gauge. There is a factory 02 sensor bung on the exhaust piping I hope to use to hook up the wideband 02 sensor. I also ordered an ethanol blend graduated vial to make sure I get a true e40 blend, and an 02 sensor wrench. I need to open up the Autolite carb to find out what jets it has in it as I don’t remember, and get a few assorted sizes ordered asap. With my super handy turbo pump, I can pump out the gas currently in the tank and pour in the e40 blend, to minimize diluting it.

Will it be worth it? I don’t know yet. I did do some additional research on the specific heat of ethanol blends, and it appears that at a 40% blend the latent heat of vaporization should be about 1.66 times that of gasoline (amount of heat absorbed). For reference, e85 would be 2.4 times that of gasoline. I am hopeful that the additional cooling provided by the e40 will make a noticeable difference in engine temp. I also need to note that there is still a fuel economy penalty, just not as substantial as e-85 or methanol. Right now the car I’m experimenting with it on is for a bone stock one and done class, so I’m not overly concerned with running out of fuel with the 15-20% increased usage.

Credit Here (E-30 latent heat appears off versus interpolating pure ethanol with pump gas)

Depending on the tuning process, perhaps I’ll be willing to ramp up to E-50 in the future, but I have a feeling that the carburetor circuits will already be maxed out with E-40. My plan to blend E-40 is a ratio 3 gallons of pump gas 91 e10 with 2 gallons of E-85. I am curious to find out how closely the local E-85 station is to true 85% ethanol content, as I’ve read that it can be as low as 51% and be legally sold as E-85. I’ve also heard it said on the interwebs, though I have no first hand experience yet, that higher percentage ethanol blends are less sensitive to richer mixtures beyond peak power air fuel ratio. I will shoot for a .8 lamda and 10:1 AFR (11.76 AFR gas referenced 02 reading) for wide open throttle. I will start with jets with 20% greater area than current jets, and see where that puts me.

As far as any damage to the fuel pump, carburetor, or fuel tank, I’ll need to take another step and drain the e-40 blend from the tank, throw in a gallon of ethanol free, and run it for a bit before storing to protect from phase separation, rust, and hard mineral crystals forming. While running this blend I intend to add an upper cylinder lube to help prevent rusting the plain steel fuel tank and add back some lubricity to the fuel. Right now I think I will use TC-W3 but there are other options like MMO, Lucas, or SeaFoam.

UPDATE: I wrote this post back in June before this car ran in its next derby, however I did not have time to play with the fuel, carburetor, and tuning before the derby, so I ended up running it as it was. Engine ran great on plain pump gas, took some hard front end shots and lost my brand new all aluminum Dillon radiator. 😦 Engine ran long enough with no water to put in a few more good shots before the front u-joint of the driveshaft got into a bind and broke. Will have to write another post when I get the chance to do the tuning on this car to run again next year.

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