E85Forum.com

jaleake@stjoelive.com · Guest

HI, I have a classic musclecar that used 96-98 octane when new in 1970. Can I mix E-85 with regular unleaded gas to obtain a mix that would give me 1970 octanes, which was common for the time? I don't want to damage my engine. Do you have any recommendations for my application?

Thank YOu,

Jerry Leake

hotrod · Joined: 19 Apr 2005 Posts: 872 Location: Colorado

It depends on how much you mix. If you are running a carburated system, you will have to realize your fuel mixture will lean out as you add E85 to the fuel in the tank.

If you add small amounts of E85, it will improve your octane based on the average of the octanes, but will also lean the mixture. If you are jetted a bit rich that may not be a problem. If you want to run higher mixtures of E85 you will have to fiddle with you jetting to get the mixture right.

If you have reliable access to E85 so you can always fuel with the same mix, you can increase your jet size a step or two and compensate for the effect of the alcohol.

Give us a little better idea of what engine/carburator system you are running and we can give you better info.

You may also need to consider some issues with gasket materials and such. If you have older fuel line hoses, they may need to be replaced. Late 1960's and early 1970's cars sometimes had fuel lines that would swell and leak fuel. My 1968 VW did that. Replacing the rubber fuel lines with modern fuel line easily solves this problem. The old Holley carburators had cork composition gaskets and these do not like alcohol very well and will break down. You would need to replace them with a modern neoprene type gasket. Also some of the 1970's era carburators had foam floats that did not like alcohol and would slowly absorb fuel and get heavy and then the carburator float would not shut off the needle and seat --- lead to float bowl overflow.

All these issues are easy to work around but should not be ignored.
You can determine compatibility by putting samples of things like your carburator gasket and a float in a jar full of E85 for a few weeks and see what happens.

If you are looking for 98 octane you will need to mix a fair amount of fuel. If you take 92 octane premium and mix it with E85 (assuming an octane of 100) to get to 95+ you would need to use a mix of about 6:4 ratio.

That is above the limit of about 20% alcohol that most older cars can handle without tweaking the mixture settings.

(92 x 6) = 552
(4 x 100) = 400

736 + 200 = 952 /10 = 95 octane

You may find you do not have to go as high as you expect with the fuel octane, as the added alcohol in a carburated system will drastically cool the air fuel mixture compared to straight gasoline. That will improve the effective octane of the mixture because intake air tempertures is one of the key control methods to manage detonation.

Larry

jaleake@stjoelive.com · Guest

Larry, thanks for the response. I have a '70 Charger with the hemi and its as close to stock as I can get it. However, I do have slightly larger primary jets in the carbs. The secondary jets are stock. The floats are brass colored metal. The engine was rebuilt @ 7 -8 years ago using gaskets of that era. I have used current fuel lines and carb gaskets, which are not cork, but paper composition. The carbs themselves are Carter AFB's and are the correct ones for this car.

I have been using 92 octane gasoline only. I thought the car would run a bit smoother with power comparable to 1970 if I the octane were higher. I know that some octane boosters use alcohol, but the cost is insulting. If E-85 will do the trick with no adverse effects, I'll use it.\

I'll also use it in my family car once I confirm that the fuel is compatible with fuel system.

Thanks for your help,

Jerry

hotrod · Joined: 19 Apr 2005 Posts: 872 Location: Colorado

Cool !!

I had a 392 Hemi I had in a 54 Studebaker many years ago, ran double AFB's on the short runner Nascar manifold to reduce the low end torque a bit so it would hook up.

Great carburators, with the brass floats you should have no problems. Some of the later Quadrajet etc. carbs used a plastic foam float that would soak up the alcohol/fuel and get heavy, causing float bowl flooding as they would not shut the needle and seat.

You might want to watch the inside of the carburators for signs of corrosion if you use high concentrations of E85, as I don't think the AFB's were annodized. Not sure it will be a problem but just something to keep an eye on.

One of the beauties of that carburator is you can change metering rods at the side of the road, so you can easily experiment with them until you get things right.

If you choose your jet size properly you might be able to come up with a setup where to switch from 100% E85 to gasoline all you would need to do is change the metering rods. Figure your increase in jet flow based on the area of the jet, minus the area of the metering rod step (on the primaries), and of course on the secondaries just the jet area.

I have an old Carter AFB book around here some where. If you know what the actual model number carbs your running perhaps I can find some useful data for you --- no promises, but will look for it and see what I can find.

With pure alcohol you need to richen the mixture about 27%. If you are good with simple algebra you can figure out a ball park number for what ever E85 mix you want to go with. Just remember with alcohol fuels they are happy with much richer mixtures than gasoline. E85 will continue to increase torque up to 40% rich where gasoline tops out at around 25% rich of ideal mixture. So if in doubt, run richer than you think is neccessary and come back down to find the ideal jetting, rather than start lean and work up.

On my WRX I just started at about a 10% mixture of E85 in a tank of fuel and worked my way up to see what would work best.

Larry

specialgreen · Posted: Wed May 18, 2005 4:09 pm Post subject: Re: cool