Could you build a "flex fuel" old school V8?

I got thinking about this today while thinking about my Olds project. Would it be possible to build a carbed V8 that can run on gas or ethyl depending on what you can get your hands on? I know there are more modern flex fuel cars but they are all injected to my knowledge.

So how about it? Can it be done and what would have to be done? Would you need to run two fuel tanks, one for gas on for ethyl or could they mix?

Heck I can always have my great uncle pass down all his knowledge of building and running a still. Granted he was making stuff to drink but I think most of it would be considered jet fuel these days lol.

Technically yes BUT E85 will eat up a carb from the inside out and you will only set it up for one or the other. The ignition tune and carb tune a dramatically different.

You will use an "alcohol" carb and dumb it down from there, tuning for max power will be pretty easy.

You'd end up creating one of those feedback carb nightmares, or end up jetting it so that it runs pig rich on gasoline. You'd need one set of jets for ethanol, one for gasoline, and to get the same sort of flexibility that a typical car has, you'd need the ability to continuously vary the jetting between the two extremes.

Run a Megasquirt 2. You can set it up for flex fuel with just an extra sensor.

Stoich on a gas engine is 14.7:1. Stoich on an E85 is more like 12:1. I can't think of any ingeneous ways to mechanically alter the fuel curve depending on which fuel you use

Maybe you could use an aircraft carb. They have a manual knob you can turn to adjust the fuel mix based on altitude. Maybe you could chase the mix around with one of those. You'd have to do it by ear since you wouldn't know what the fuel mix is. If you have 1/4 tank of gas and you fill it with E85, you'd have to guess on the A/F ratio by ear

Or you could do two tanks. When you switch tanks, just turn the knob when it starts running funny :)

I have a friend who built a low budget, low tech 1980 corvette drag/street car that runs on E-85 with a carb....I will try to find something out about how he did it.

(I haven't talked to him in a while)

One of the reasons I was curious is I recall hearing tell of a cross continent (and I think world) racing off road rig that was setup to run on anything they could get their hands on. If I recall correctly they said it could run on anything from "High octane to camel piss" lol. I believe they said they did run it on ethanol a few times as well.

I think the rig was a old Land Rover but I could be mistaken.

The issue is not so much getting it to run properly, but rather telling the computer how much fuel to inject.

A flex-fuel vehicle has sensors that detect what type of fuel is being delivered to the injectors, then it modifies the stoich mix based on the O2 sensor signal.

If you have an alcohol compatible carb you can get close with just fuel pressure changes. 20-30% extra fuel on E85 is about where you want to start your tuning. With the EFI cars I've played with it's closer to 15% cruise (stoich) and closer to the 30-35% range at full load.

You might be able to make it work if you run a Rochester carburetor. That uses tapered needles to regulate the gasoline, and you could work up a method to raise the needles for the ethanol.

Alternatively, you could go with a modified manifold and two carburetors, one for gasoline and the other for methanol. Just use a flapper to switch between them.

I can see it doable with EFI... as you can customize the tune per each fuel. As mentioned above you can even run a sensor linked in with MS2 and let it do the detection work.

I don't know enough about carbs to say on that, although it sounds like it isn't as easy as filling up on another gas... but actual carb adjustments, swaps etc...

I would suggest a throttle body injector and MS. Simpler install than a full FI system, still would have the ability to switch back and forth. But I know nothing, so caveat emptor.

I've thought about building a carbureted E85 engine, but not trying to make it flex fuel.

Ideally, IIRC, you'd run a bit higher compression ratio to squeeze a bit more efficiency out of the ethanol (versus just dumping 30% more fuel into the thing and running alchohol-safe components).

But...where I live we apparently have more ethanol pumps, per capita than most places (I guess we were highest at one point).

Clem

foxtrapper wrote: Alternatively, you could go with a modified manifold and two carburetors, one for gasoline and the other for methanol. Just use a flapper to switch between them.

you know it is really funny I actually thought of this as a solution lol.

injection seems like the optimal route for this sort of setup I just really want to avoid it on this car. I want to make the car as basic as possible, but then I guess this sort of fueling is far from basic lol.

I may just take and as I rebuild the car make sure it would be reasonable to swap over if the need came about (eliminate parts that would corrode with the ethanol and a fuel pump that won't cause a spark).

Even with injection you will need the sensors and a flexible computer that can hold not only two maps but the blend map as well.

The reason OE fuel system engineers get paid is by figuring out the math between 87 octane and E85 and making all fuels and blends work on their vehicle.

Paul_VR6 wrote: If you have an alcohol compatible carb you can get close with just fuel pressure changes.

The only thing that will do is overpower the needle and spill ethanol all over the engine. Carbs are passive. They only use pressure to fill the bowls. Adding pressure won't push more fuel through the venturi, it will just push it past the seat.

Kinda like adding pressure to your toilet. Adding pressure won't make it flush faster, it will just add pressure when filling the tank.