WackyRotary

I have ran pure E85 before. I have a weber and have some alternate main fuel jets and larger accerator pump nozzles, but they are not the best ones to keep from getting stumbling when slamming the gas. It does make slightly more power and nice smelling exhaust, but really goes through fuel fast.

I am not for using it though because when you compare the E85 BTU cost per Gasoline BTU cost, E85 costs more to drive the same distance. I have caluculated if gasoline is $3 for example, E85 must be ~$2/gallon for the costs to be even to get the same miles for the same amount of money.

E85 ~81,000BTU's a gallon
Gas ~114,000BTU's a gallon

Do the math, you will find the same answer. The problem is, who ever controls gasoline prices also increases E85 to go up at the same rate, so its ALWAYS a more expensive per BTU. It is however a good performance fuel if you can run some high compression or boosting engine though.

inuissus_cendi

Exactly
In current normal engines its not good and doesnt make as much power, but with high compression (not really viable on an old rotary) or boosted applications it can help alot. Some Stanford grad students just put out a paper on the topic of direct ethanol injection only during high boost on a turbo charged car. They rigged up some sort of ECU to change the mixture to favor ethanol more when it sensed knock. It's a really sweet idea with great results. Google it if you're bored, cant remember where I saw it.

laundryhamperman

iTrader: (3)

OK, first to lay to rest the octane rating. Its either the ASE or MIT that has a standard engine. The take a fuel and test it under certain conditions and compare when it knocks to when a mixture or Isooctane and something else(normal pentane, i forget, but it loves to detonate!) starts to knock. The mixture is (octane number) % isooctane and then 100 - (octane number) % the other hydrocarbon. 93 octane fuel will knock under the same conditions as a mixture of 93% isooctane and 7% the other hydrocarbon.

For fuels above 100 octane rating, it is measured as comparable to how many cc's (cubic centimeters) of tetraethyl lead you add to a gallon of isooctane. 110 octane fuel gives the same knock tolerance as a gallon of pure Isooctane with 10 cc's of tetraethyllead added. To cover questions about the R+M/2 rating, there are 2 different ways of testing it. R stands for research method. I forget what the M stands for, but it was developed by the military(air force i believe), so they take the average of the 2 numbers and we get the rating we see at the gas pump.

The point is that it may be a fuel that has no relation to Isooctane but it still has a legit and real "octane rating" as we have decided to call it.

Secondly, from what i've read, you can add 10-15% ethanol or methanol to pump fuel to almost any internal combustion engine so long as the octane rating and fuel mixture are appropriate and it will not have any ill affect. I might or probobly am wrong on this next suggestion, but is that E-85 85% gas and 15% ethanol, or maybe i'm thinking of Gasohol, but in any case....

and for reference, i'm getting my information from a book entitled "The internal combustion engine, in theory and in practice" and it was volume 2 covering the chemistry of combustion

mr_ouija

E85 is the other way around, 85% ethanol and 15% gasoline. I think you're right that the 15% ethanol 85% gas is gasohol

inuissus_cendi

edit: I reread the first paragraph and now it makes more sense. So basically when they say ethanol has an octane rating of 110 it knocks at the same point as 100% isooctane plus 10cc tetraethyl lead? Thats sort of how I guessed they did it, and I guess it works. They're just finding new ways to keep using the same stupid scale. But anyways, my point was that its not truly an "octane" rating as there is no octane.

It really seems like it would be a great fuel for boosted applications though. As soon as I get some cash I've got a fun idea I'm going to try using small amounts of ethanol at just the right time.

and wacky, was that on your turbo engine? If so how was the knock suppression? Did you try upping the boost at all while on E85?

WackyRotary

(and wacky, was that on your turbo engine? If so how was the knock suppression? Did you try upping the boost at all while on E85?)



I only did it with the n/a setup. This is with weber carb and header. I have a carb and no way to change the ignition as it was a locked distrubuter.

Whizbang

you can get better mileage than the gasoline equivelent if you build your engine with the fuel in mind. obiously the entire fuel system has to be prepped to handle long term alcohol use. Just adding to your existing vechile is going to leave you with all kinds of problems, including but not limited too 1) internal rusting of gas tank 2) death of fuel pump 3) death of rubber fuel lines 4) failure of injector seals 5) internal corrosion of exposed aluminum fuel rails.


i plan on making my 1/2 BP project run on E85 when its more readily availble in my area. I am going to use 9.4 comp rotors, and a turbocharger and some serious tuning. with proper compression (as ethanol favors the "Variable" compression turbo engines provide) and correct timing. you can have more power than standard gasoline, and get better fuel consumpation at the same time, while saving at the pump)

WackyRotary

I have to disagree with the MPG being better with E85. Since the BTU content is less, you will use more to go the same distance, its simply logical to understand this.

E85: 81,000BTU's/gallon Gasoline 114,000BTU's/gallon

"Roughly" ideal a/f of E85: 9.1:1, gasoline a/f 14.7:1. You use more E85 to produce the same amount of work. Best power is closer to 8.5:1 for E85, and 12.5:1 for Gas. The oxygen content of E85 is greater, so it can make slighly more power especially with great compression or boost.


Example: if you car was getting 18MPG on gasoline. It will under ideal conditions get roughly 30% less MPG with E85 depending how lean you can run your mixture. With all things being equal- same stock compression 12a rotors, it will never be as good for MPG. Power increase will be slight though - the one benfit.

Alex-7

https://www.rx7club.com/showthread.p...ight=Moonshine

inuissus_cendi

BUT if you build an extremely high compression engine you can make up for the smaller amount of chemical engergy in the E85 vs. the standard gasoline. All of our current engines are built to a low enough compression that they don't knock. We don't tap into the true potential of ethanol-based fuels until we get into high compression. I wonder what the magic number to achieve better mileage out of E85 is though.

The higher the compression of an engine, the more efficient it is (generally speaking). So yes with the same amount of E85 and normal gasoline, the gas has more potential energy. The best gasoline engines only have an efficiency of about 30% (rough figure, but you get the idea).

So if you get a 30% efficiency (which, remember is a high number even for modern engines) out of your engine running normal gasoline you will only get 34,200 BTU of energy actually converted into work.

If you can achieve a 43% efficiency on E85 you will get more energy converted to work (34,830 BTU), and therefore more power and better mileage.

Now I would try to calculate the change in compression ratio needed but there are way too many variables for me to get it right. Even PhD. automotive engineers can't quite predict the efficiency of an engine. I don't even know if an engine on E85 could keep from knocking at that high of compression, but I'm sure we'll all find out in a few years time.

WackyRotary

I am definitely going to say, you'll have a hard time getting a rotary to achieve those types of numbers- especially a 12a with 9.4:1 rotors and a carb. I've never heard of 30% for a gas engine, thats more like compression ignition engine range. But you'll still get it to run.

inuissus_cendi

Oh I know the high compression thing isnt something I'm trying to achieve, its just a theoretical for future cars. Also if you turbo it you get more compression. (not a higher compression RATIO but still higher compression)

The 30% figure was just something I pulled off a website for an example, I'm not sure of the truth in it.

neektar

iTrader: (2)

So less octane is better for N/A rotary engines? How about modded N/A rotary engines
BP?
SP?
Stock Port?
PP?

All N/A of course. I just put regular in my tank and I wanna make sure I did the right thing.

81gsl12a

iTrader: (1)

yes you did the right thing...no need for good gas unless you are turbo

neektar

iTrader: (2)

Feels good to do the right thing. She's preforming pretty much the same, I did notice a smother rev, not sure if it's the gas though.

FAQ?! Yes!