Science question: Is mixing e85 and 93 Octane gas any better or worse than just gas?

Scott

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I have read a few things lately about the possibilities of mixing E85 with premium gasoline to both save a little money and get a tiny octane bump. my car requires premium fuel because of the big turbo and what not, so I was wondering if anyone else had tried a 50/50 mix or any other kind of mix for that matter, and if you have what did you notice?

I know that E85 has less thermal efficiency than gas, but I was really thinking more along the lines of possible fuel system damage in a system built for straight gasoline.

What do you think, or what have you seen?
 

_HighVoltage_

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I'm not sure about E85, but I'm guessing it's not a very good idea. My Polo requires 95 octane gas and I've tried running it with 89 octane - it was considerably slower and the engine didn't sound good at all (a lot noisier and I think it was misfiring)
 

airmenair

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Yea you could be running the risk of damaging your fuel system if you use up 50% E85, that said I'm not sure at what concentration E85 becomes corrosive to a gasoline fuel system. Small doses are OK, keep in mind gasoline has up to 10% ethanol in it nowadays and E85 has somewhere along the lines of 10% gasoline in it. Also, how would it save you money? Last I saw E85 was still more expensive then the highest available octane of gas? I could be wrong on that though.
 

Scott

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E85 has an octane rating of 104 or 105 depending on who is calculating it... oh yeah and I am talking about USA octane ratings here just so everyone knows. My regular gas octane rating is 87, mid-grade is 89 or 90 and premium is 92 or 93 depending on where you buy it.

I higher elevation states it is very common to see 85, 87 and 91 because of the decrease in oxygen you get at altitude.

Oh, and just so we don't re-hash this... yes I am aware that octane rating is not a rating based on performance of any kind, but a rating of the fuel's resistance to pre-ignition. I am basically looking at a possible way to save money on what is a pretty expensive car to drive even at it's most efficient state, and given that fact that it is modified and tuned right on the edge for 93 pump gas, i was thinking that the mix would give a little octane bump and reduce the chances of knocking at WOT.... AND save me a little money at the same time. I was just hoping someone here had tried it, or had a first hand experience they might want to share.

Ok, back to the question at hand!
 

Scott

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E85 is $1.50 cheaper per gallon here than premium
 
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I don't know about E85, but the what I've always heard (whether it's true or not) is that switching to ethanol blended (the regular non-E85 kind) after having always run on non-ethanol fuel is not a good idea.
I don't remember exactly why, but something about crud suddenly coming unstuck in the engine when you go to ethanol.
 

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It's the lines in your fuel system that are the main issue here. If the hoses and gaskets are made from rubbers that dissolve in ethanol, no amount of money you save will be worth the problems. Your "E42.5" mix might not be as immediately corrosive as E85, but over time you'll have the same problems. Replacing those problem pieces is the only way to be sure that mixing the two is not a problem, and even then your mileage will suffer thanks to the lower energy density of ethanol. With that in mind, good luck if you do decide to go through with it.
 

Redliner

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It's the lines in your fuel system that are the main issue here. If the hoses and gaskets are made from rubbers that dissolve in ethanol, no amount of money you save will be worth the problems. Your "E42.5" mix might not be as immediately corrosive as E85, but over time you'll have the same problems. Replacing those problem pieces is the only way to be sure that mixing the two is not a problem, and even then your mileage will suffer thanks to the lower energy density of ethanol. With that in mind, good luck if you do decide to go through with it.

You are right.
Brazil has been using 20-30% of ethanol mixed to the gasoline for ages, and everytime a car is imported to be sold here they need to adapt the fuel lines because of that.

I also heard about what ESPNSTI said, but I don't believe it 100%.
 

thedguy

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Much of the US has been running around a 10-20% mix of ethanol in all it's gas (many of the fuel pumps will say right on it "10% ethanol").

Everything I've always read on the subject has said that too much ethanol on a car not built for it will eat the seals. Also when it gets cold and sits for a while the fuels will separate exacerbating the problem.
 

Susurrate

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Yeah, don't do it. Your MPG will go down and the seals and hoses in your fuel system will begin to rot due to the ethanol. As for cleaning all the crud out that is more of a problem with transportation and storage of ethanol. Ethanol can't be shipped via existing oil pipes because the ethanol will clean the crap out of the pipe contaminating the ethanol and causing leaks in the system. You also can't separate shipments of ethanol with water like you can with oil.
 

C53A_4G63T

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Your iinjectors need to be able to handle a large increase of fuel. Usually twice the CC's that are currently in the vehicle. If you run 100% E85. And of course the lines must be changed to stainless steel. Kinda doesn't make sense right now when you end up using twice the amount of fuel than normal gasoline. Even if it is cheaper.
 

thedguy

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Honestly, I'd see what the VW/audi guys are saying. Seeing as your car is turbocharged you can take better advantage of the extra octane by mixing in a bit more ethanol. If the fuel system can handle it, I'd considering doing it and having it tuned on the dyno.

When the motors are built/tuned for the job they tend to gain power and not sacrifice much for fuel economy. Or so I hear.
 

awdrifter

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As said above, E85 is more corrosive than regular gasoline, so you'll need to replace the fuel pump, fuel lines, and injectors with ones that are designed for E85. Another thing is E85 has less energy than regular gasoline, so you'll need bigger injectors and possibly a retune. I would say it's not worth it in most cases. But if you're running very high boost and the 91 octane gas won't do, then switching to E85 is worth it.
 

Scott

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I am going to do 20% of my next fill up with E85 and see what happens
 

Ottobon

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I know that E85 has less thermal efficiency than gas,

BIZZZ, WRONG. In labratory studies people have got the same or higher thermal dynamic efficiency out of ethanol as diesel using properly tuned 19:1+ compression and trick EGR systems. Don't however confuse thermal dynamic efficiency with BTUs per Gallon of gasoline, because thats not the same. The difference is Ethanol (like diesel) doesn't chuck nearly as many BTUs out the exhaust.

I did some simple calculations and 20% E85 (17% ethanol) should be equivilent to 95 Octane gas when mixed with 93 Octane. Just make sure you take advantage of that octane, or as everybody else has said it won't be worth it.


Personally, if i had the money i would really like to convert engines to ethanol and then go crazy with it, it just burn is just so much more controlled and useful then petroleum.


Oh, and on a side note, i think flex fuel vehicles are the stupidest things since purses for men.
 
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