Are F12’s in the USA optimized for 91 octane?

Engine nowadays are able to adjust injection timing based on input from antiknock sensors, so the engine will adjust to your octane level. Obviously you will get more power with more octane though.

 

I wish it was that simple.

Yes, if the fuel quality is good, 91 AKI is fine.
A typical European quality 95RON has a MON of 87.7 or higher. Even the cheapo 95 we have is rarely below MON 87.5. When it comes to resistance to detonation in a performance application with a high dynamic cylinder pressure, the MON is important.

Unfortunately in the US, there are no laws dictating what the fuels should be. Some states, e.g California are notorious in the industry for its poor quality fuel. A 91 AKI fuel with a MON of 84 and a RON of 98 is perfectly fine in a low compression lazy engine found in the soccer mom Tahoe or Toyota grocery getter, but it is useless in an engine you push. If you putt around town in an F12, it will work fine too, but as soon as you stab the loud pedal and get some heat in there along with higher dynamic compression, it will pull timing as to not detonate. Ferrari chose a less conservative approach for the 812 by simply saying 93AKI. Will an 812 run fine on a quality 91? Absolutely, but it is hard to find in the US. There are states who generally have pretty good fuel - I believe TN and MI are two of them.

Anyway there is one last thing that also have a major impact on the fuel, and that is its lack of longevity. Modern fuels go bad ridiculously quick compared to 30 years ago. After a few weeks there's a difference, and after two or three months it is trash. I'm not talking about it gumming up or varnishing, but simply the fact that octane drops and the E10 stuff collects water.

So the answer regarding what fuel to buy has an answer which contains the following points.

1. Get the highest octane you can. If a 93 goes bad, it is stll better than if a 91 goes bad.
2. 93 AKI is much more likely to not only have a proper MON, but it is also more likely to be a better overall product.
3. Buy your fuel from a station that sells lots of fuel. If the place do 't sell much, chances are that what they have in their pumps, have seen better days.

Lastly, if your car is going to sit with the fuel in the tank for more than a month, add a fuel stabilizer. Make sure you take the car for a spin to not only mix it well in the tank, but also to get it into the system and engine.



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really? I've lived here all my life, driving lots of high end cars, race cars, rental cars, boats. NEVER had a problem with fuel, from cheapo to highest priced stations. One time the wife put gas in a diesel rental, but that's a different story. . .

 

100% agree never an issue.

 

Two things to keep in mind. First is that you will not have a problem, just slightly diminished performance. Secondly, it is something that has become increasingly problematic over the past 20 years as emission rules have changed, as has the fuel formula. Want to find people with lots of issues in the boat world? Go to Offshoreonly and ask the high performance boating crowd about fuel longevity, E10 fuel and detonation problems. Trust me, it is very real. I've been a powerboater myself, and I know first hand what kind of issues you'll run into if you run crap fuel in a pair of 700SCI's. Mercury Racing have doen many things to prevent problems, but that does not mean 90AKI with low MON is okay, because it is not and your 38 Lightning will be down 8-10 mph up top.

No problems? Ask the classic car crowd how they like the E10...

In the mid 2000's, Koenigsegg chose to not run a standard style antiknock system in their cars, and thus they actually had to detune cars sent to the US. A Koenigsegg CCX was down about 60-70 hp in the US. If you check into the racing crowd of people running turbocharged and supercharged domestic and imports, a very common debated subject is fuel quality issues depending on where they live. Ask any good engine builder or tuner in Cali and they will tell you that they wish they could get some proper jungle juice.

Sometimes you need to give it a try. Remember 458Trofeo? He used to only run 100AKI in his 458 because after trying it one day, he found it to make a significant difference compared to the usual crap fuel he found in his LA area.

And again, when I say in the industry, I'm taking about people working in the oil industry. US fuel quality is a common topic. Due to the EPA they have had to change so many things in relation to how they increased octane, and it has become a massive challenge to produce a fuel that is both cheap and has a sufficient octane as well as shelf life.

You can believe me if you will, and don't if you won't, Either way is fine with me. I did not post my initial post as a smackdown on the US, it was simply to provide an answer to a question.

 

There's a difference between issue and not being optimum.

 

Summary for me as a tifosi in LA - Ignorance is bliss since we can't get 93 oct (so long as 91 hopefully won't *damage* anything)

I'd on occasion mix in some 100 octane race fuel from the 76 in Pasadena with the 91 (a pain for me), and felt like I got a bit more oomph in my GT3. But maybe placebo effect.

 

It does not hurt anything, that's why there's a knock sensor. But it will pull some timing when it senses a ping.

 

Well next time I fill up I’ll try to optimize all the octane’s that are available to me.