1st Generation Specific (1979-1985) 1979-1985 Discussion including performance modifications and technical support sections

Can a stock 85 rx7 fb gsl run on E85

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Old Nov 10, 2019 | 10:25 PM
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Can a stock 85 rx7 fb gsl run on E85

I've searched around here and cant find anything about E85 on first gens (mostly just other gens or personal problems). I know E85 requires more fuel so the chances of needing a larger carb could be probable but im not sure if the fuel lines or even the gas tank will be affected
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Old Nov 11, 2019 | 01:35 AM
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I can't remember the exact figure, but I think you need something like a 1/3 more fuel to run E85 due to the lower calorific value.
I don't know how much flow the standard pump on your car produces but you may need a bigger fuel pump.

Also on a carbed car it makes less sense as you need to re-jet every time you switch between E85 & normal petrol, a car with EFI can just run a flex sensor & a map that can switch between the two fuels.
Additionally I've read that ethanol can have a corrosive effect on old rubber fuel lines & fuel pumps. I have no idea if this is an internet myth or true but it bears thinking about.

So the answer is not without modification & not easily. And if the cars stock, what's the point?
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Old Nov 11, 2019 | 05:53 AM
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I honestly would not. It will service no purpose and may end up causing you headaches in the long run.
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Old Nov 11, 2019 | 07:40 AM
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It will eat hoses, carb seals and run like crap, but go ahead and let us know how it does.
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Old Nov 11, 2019 | 07:45 AM
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lol
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Old Nov 11, 2019 | 10:15 AM
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From: https://www2.mazda.com/en/100th/
we did the conversion on a miata, and its a nice race fuel.

you need:

about 30% more fuel, Alcohol has less energy in it (CH12 vs CH18 for gas). this would require a complete re jetting of the carb. and you may run into an issue where you cannot buy jets that big, or the passages are too small.

you will need a larger fuel pump.

the alcohol will act like a solvent, so the first few tanks will clean out some junk, and you'll need to change filters a couple of times. any original 40 year old fuel line will probably die. fresh hose does fine.

you will need to premix, as the normal premix, and the metering pump oil is not compatible with alcohol.

in short, its probably not worth doing, unless you're actually racing.
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Old Nov 18, 2019 | 04:36 AM
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Not worth doing it
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Old Nov 18, 2019 | 05:48 AM
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Originally Posted by j9fd3s
we did the conversion on a miata, and its a nice race fuel.

you need:

about 30% more fuel, Alcohol has less energy in it (CH12 vs CH18 for gas). this would require a complete re jetting of the carb. and you may run into an issue where you cannot buy jets that big, or the passages are too small.
I have heard of people running their carbs without jets at all as a starting point, then drilling the passages above the jet to get more fuel, in certain applications..

you will need a larger fuel pump.
You need a larger fuel pump no matter what, the stock Mazda pump is laughably undersized and can't even supply 100hp worth of fuel if the pump of filter have any degradation at all.

the alcohol will act like a solvent, so the first few tanks will clean out some junk, and you'll need to change filters a couple of times. any original 40 year old fuel line will probably die. fresh hose does fine.
The reason for this post. I usd E85 to try to flush out the fuel tank in my '81, five gallons at a time. This is two week old E85.



you will need to premix, as the normal premix, and the metering pump oil is not compatible with alcohol.

in short, its probably not worth doing, unless you're actually racing.
The other reason I posted... alcohol compatible premixes seem to leave large amounts of gummy tar-like deposits everywhere.

So yes, maybe just fine for a drag engine or big single FD that might only see 1000-2000mi between engine teardowns, but not so good for anything else, and rather pointless too, since you don't need the additional cooling in a stock 12A.
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Old Nov 18, 2019 | 09:34 AM
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From: https://www2.mazda.com/en/100th/
Originally Posted by peejay
You need a larger fuel pump no matter what, the stock Mazda pump is laughably undersized and can't even supply 100hp worth of fuel if the pump of filter have any degradation at all.
.
actually the stock pump is quite good, its does a decent volume at a rock steady pressure. the holley regulator made the flow worse, and pressure is all over the place
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