My vote is The 91 oct 0% eth

Gasoline has a higher btu per pound output than ethanol.

I suspect that, and you need to check your owners manual, your factory tune is set for 91 octane. More octane is not always better. (Octane is resistance to detonation, nothing related to "power", bla bla bla).

 

There is an old "family" run gas station a few miles from my house that has a pump for 93 octane 0% ethanol. I run that in my formula ford and in my 2013 Evora S. I have no data on performance or mileage but personally I think that would be the proper gas to run in this type of sportscar.

 

Even as antiquated as Lotus can tend to be, I can't imagine low ethanol content having a detrimental effect on the systems in the car. Tune-wise, it'll run best on the octane it was designed for and listed in your manual. For a modern car, I'd aim for the octane rating and nothing else. Any lower and you lose performance, any higher and you waste money (unless the higher rating is cheaper thanks to ethanol)


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It is a Toyota engine, 10% ethanol is nothing, the seals and hoses we handle that as most of the country is at least 10% E. Yeah Ethanol is a "cheap" octane booster. As someone said, low octane will hurt performance as timing will be scaled back from ideal settings, higher octane will not hurt your car but make not add benefit, the ECU will not advance timing beyond factory limit. Some one above said octane will not boost power, that is literally correct if nothing else is changed. BUT, higher octane resists pre denotation thus PERMITS the engine manufacture or tuner to design in for advancing the ignition, which will boost power. What the OEM does is use a more aggressive timing curve, but as a safety net for bad or wrong gas the computer will retard ignition is pre denotation (pinging) occurs. Thus reducing power too.

 

In Luxembourg, we don't have access to fuel with ethanol (yay!!).
Our "guys in charge" seem to have figured out from the start that it's just a big scam and not actually good for the environment.

My cars drink fuel with a 98 RON rating, that's 94 octane in the US.
95 RON would be just as good for the Elise, especially if I'm not red-lining her. 95 RON would be 91 octane in the US. That's our "worst" fuel here.

 

You are very lucky. Thanks to corruption and stupidity, we in the US are not so lucky. Not only is it not good for the environment, it's actually very detrimental to it in the US.

 

Interesting how all this tune stuff rarely mentioned what car was set for. Of course its 91 because the left coast doesn't get the good stuff. That is a default in the industry.
Julian, by chance, with your tune etc, were you told to run 93 octane? On my STi difference between the stock tune and 93 octance was ~20+ HP! Always wondering what an otherwise Stock S would have for HP if tuned for 93 octane (which I run daily in all vehicles requiring premium).

 

John, good points! I did not mention the option of tuning for higher octane, as I didn't want to add complexity to my answer nor take the wrath from the crowd of "what about us without a tune".

As to my car yes it is custom tuned, yes it runs on 93 +10%E that is standard premium in Texas and thus was tuned to any advantages of 93 over 91

 

Would tuning for 93 v 91 octane be good for ~20HP in our motors?

 

I don't think so, but only true measure would be to optimize tune to each grade and see. I didn't even get 20% increase from stock to optimized with the 93. I feel Lotus probable left less on table that say Subi.

 

I also left the subject of our stupid ethanol out of the debate. No unfortunately a typical car tuned by OEM for our fuel (cough) syrup will have decreased power if run on the no E blend of same octane. Reference Grassroots Motorsport mag, fuels tests on Mazda MX5. I say typical because maybe Lotus does even consider tune map tweaks for US market.

 

2 things, the octane rating you see on the pumps, is the average rating and not always accurate. That is why sometimes after you fill up the car seems a little sluggish and other times it just feels so much quicker.

It has been mentioned that running a car at a higher octane will not hurt the engine, that is not entirely true. If your car was designed for 87 and you run 93, you will hurt the engine over time, that is a proven fact. Just like running a car on 97+ octane (Racing fuel) that is designed to run on 91 will hurt an engine over time.

Several auto makers started putting octane and RON ratings in owners manuals just because of this issue.

Here is a link, that you might find interesting about gas -

Gasoline - Wikipedia, the free encyclopedia

 

Randy, I am sorry but I must disagree with a few of your points. One high octane by itself will never harm an engine, now how that octane is achieved is a different matter. Effects of lead on cat converters is well known, but back to products that still qualify as gasoline not other hydrocarbon blends, methods used up to 105 RON+MON/2 are reasonable.

Also notice I did not use the word average, it us not say a mean RON but they erase of two different test methods. A blend would always get this same average not a high low variation. If fact the US/Canadian testing system is more accurate than just the Euro RON system, as MOM test is closer to real world. Please read the link to Octane Ratings http://en.m.wikipedia.org/wiki/Octane_rating in the link you provided.

 

Im not a chemical engineer, but I know when I put 0% ethanol in my track motorcycle my butt dyno tells me its smoother and faster then pump gas with ~10% ethanol. If I had the option to buy 0% ethanol I'd choose it every time. I feel like its rubbish.

 

So...we're saying that since the stock Evora is likely calibrated for 91 octane, going higher does not add anything, and that lower ethanol is better than higher ethanol, and hence the answer to my question is 91/0% (as opposed to 94/10%)? Or are we saying it doesn't matter much?

 

I am saying it doesn't matter much.

 

Higher Octane will result in less knock and allow the ECU to run max timing and more power. But if the car already has 0 knock on the lower octane, you wouldn't see any gain upping the octane.

It takes about 30% more fuel on E85 to reach the same AFR as gasoline/race fuels. Resulting in 30% less fuel economy, though E85 is higher octane and has the potential to support very high horsepower.

To determine if switching from 91 to 93 or 91/E10 93/E10 would add benefit or produce unfavorable results, one would need to log knock and timing. Then determine MPG with the same driving. The Ethanol blend in theory should produce slightly less fuel economy, but due to the small percentage it may be unnoticeable, especially with the many variables of weather and driving style.