E85 and Pro Flo 4

Let's get one thing straight. Edelbrock does not support this fuel with and makes it very clear with a note in the Fuel Requirements section of their instructions saying "E85 fuels are not compatible with any Pro-Flo 4 EFI systems." So if you go down this path and have any issues don't call Edelbrock's tech support for help. You are on your own except for support from fellow hotrodders.

That said, rumor has it that all the Pro Flow 4 components are E85 compatible. The only piece I would question is the aluminum fuel rails.

Why do this? E85 is a little cheaper per gallon than regular gas and has an octane of roughly 105. Maybe you have an older engine with 10:1 compression that knocks on premium gas. Maybe you've got an engine in the 9:1 range that "needs" a supercharger. Maybe you are building an engine from scratch and want to bump the compression up in the 11-13:1 range to pick up some power. Some of that power is from the higher compression, some of that power is because alcohol brings a little of the oxygen needed for combustion with it, and some of that power is because evaporating E85 cools the intake charge making it more dense. Sort of a liquid supercharger.

Why not do this? E85 has 30% less energy per gallon than gas. This means you have to fill up more often and typically costs more than gas per mile driven. Since it runs cooler than gas it's not a great winter fuel. By far the biggest issue is that E85 will attack parts of your fuel system made from rubber, aluminum, brass... and it pulls moisture from the air so I suspect it's pretty hard on steel tanks too.

Me? I live in the Midwest where E85 is easy to find. I'm running it in my 1982 Jeep CJ-7 and my 2021 Jeep Wrangler. Both of these are summer toys. I like the fact that ethanol is a renewable fuel. I like that the exhaust doesn't burn my eyes and nose when cruising with the top off. I'm sold!

It's hard just to figure out what the octane of E85 is. It behaves different than gasoline, less sensitive to compression and more sensitive to sharp edges in the combustion chamber, but generally accepted to be about 105 octane. But the ethanol varies around here from 80% in the summer to 50% in the winter and that's got to change the "octane." What to do?

I had high hopes of road trips running E85 when I can get it and Premium when I can't get it. I may have assumed wrong that the EFI system could learn to deal with all of the above.

I have elevation to deal with here in Colorado, about 5400ft. My build will either be 13.25:1 or 13.7:1 depending on head gasket thickness selected during assembly. That said, I’ve read of much higher compression without issue. For the street I’ve read 13:1 is max. I loose one point of compression for elevation so I’m hoping I can go 13.7:1. A cam closing intake at 41 degrees gives me an effective compression ration of 11.1. It’s my understanding that compression has decreasing return after 12.1 on the high side and less than 10.1 on the low side.

I’m hoping to be happy with the NA power. Again with altitude I only expect 6psi from a torqstorm putting me around 15.5-16:1 effective compression ratio. I’d add water meth to the torqstorm but from my research, believe e85 would be sufficient.

You are correct, this is not a flex fuel system, but all is not lost.

I suspect the Pro Flo 4 would do a pretty good job of adjusting once the coolant temperature hits 160 degrees and it switches to closed loop mode and corrected A/F ratio using the O2 sensor. Closed loop it can adjust fuel flow up to 30% so it is possible to have a single tune and switch fuels. Prior to that it would run in open loop mode and really flood the engine (or be really lean if Premium were your baseline).

I am confident you could come up with two tunes, one for Premium and one for E85. Then you could run the tank low before filling up and switch tunes when switching fuel. Ideally you would create each of these tunes on the dyno starting with a different base map. One advantage to this approach is you would also be switching ignition curves, I suspect you'd need to dial back the timing when running Premium at 12.5:1.

Edit:

I forgot to say that both tunes would need to use the same injectors and fuel pressure. Most likely a single Cal with injectors and fuel pressure splitting the difference between E85 and gasoline so the ECU would adjust 15% one way or the other. Message me when you get closer to doing this and I'd be glad to help figure out your baseline settings.