100 octane fuel. Waste of $$ in a stock F12??

I like theorizing but I like data better.

My guess would be, as you said, little to no difference due to the calibration being optimized on 93 octane. (or less).

Only way to know for sure would be to do before/after dyno testing. Could run it before/after at the dragstrip as well but likely too many variables for what will likely add up to a very small if any difference.

A different calibration for 100 octane would likely benefit your Alfa being of course forced induction. Much less so (if any at all) for the naturally aspirated F12.

 

there is a massive and ongoing debate thread in the 458 section on this topic, I believe Carlo (458Trofeo) started it. Given that, my safe harbor statement is "this is what I believe to be true"....

The ECU's in most modern cars are tuned for specific octane ranges; some cars (eg. Ferrari, BMW M, etc) specify higher pump octane (91, 93) since the mechanicals and electricals are tuned for it.

Most/all ECU's will optimize the timing around their ideal map - i.e. what they are programmed to expect. If/when conditions are better (eg. higher octane fuel), they self-limit to their map. On the other hand, when conditions are worse (eg. high temps, ignition detonation) they will retard performance (eg. advance, among other things). So, if you run 89 octane in your F12, the sensors will likely notice the effects and retard performance. Also happens if you're running your car hard on track on a hot day, the MAF detects hot air, hot engine, and starts to back you off. "Limp Mode" is an ultimate form of backing the engine off due to a problem.

So....no, 100 octane won't make a difference, UNLESS the fuel you're using normally is below 93, or has some other limitations. Ethanol content also will impact it, to the extent it varies in the pump fuel you're using. We've dyno'd the 458 Challenge cars using VP Race Fuel 100 and pump shell 93; we can notice differences in the detailed output, but then again the race car ECU is adapted for race fuel.

100 octane does burn differently than 91/93; most say that it will accelerate the degradation of your cats since more fuel is burned downstream (higher octane, slower burning, "cooler"). It's another reason that running race fuel seems to create more of the pops and burbles people like (or, shoot flames out the exhaust).

As an indicator, a lot of VW and Audi owners use APR software tunes on their cars; APR specifically programs their various tunes based on fuel grades.

Race fuel does "smell better" (since the car is burning a lot downstream). Some folks claim to be able to feel a real difference, some not. To me, it's like drinking tap water or Evian, if you like it, go for it.

As for your 4C, again assuming your "normal" fuel is actually 93, the ECU will run things better since it's not fuel performance limited, but assuming no other issues, that's probably more an indictment of your usual fuel than a result of using 100. FWIW, my daughter's race kart uses a spec VP 93 race fuel; we get fuel tested all the time, you'd be surprised at how variable pump fuels are in terms of quality and ethanol content.

 

Good post. I agree with most other than higher octane equals slower burn rate. Most gasoline burn rates are similar and if anything higher octane would be faster burn rate but still no direct correlation with octane.

 

If the cars not tuned for it, you're wasting money and possibly hindering performance.

 

GREAT post.

I believe this to be true as well. The only car of mine where I notice any difference is my F40 and basically, the difference I feel stops at 96 or 98 (remember that I'm at altitude). The times that I have thrown 100 in any of my other Ferraris, I gotten a CEL related to the cats and I haven't felt any improvement at all over the normal high octane.

 

... higher octane is about delaying detonation... engine knock is about fuel mix igniting before it is ready... calibration determines when ignition occurs, which can affect when best power is produced... the temperature at which fuel burns determines the BTU (power) created by the detonation... using higher octane fuels that can NOT be utilized is a waste as it does nothing

 

93 octane pump gasoline is (RON+MON)/2 also known as AKI. What scale is the 100 octane you are buying? RON, MON, (R+M)/2 ? 93 AKI is equivalent to 97.5 RON. RON is the scale used in most of the world. A good racing gasoline will provide you with RON, MON, RVP, and many other details. Is the fuel oxygenated?

 

Unless you're a racecar driver, there is no point. Seeing as no one actually competes with a road car, even for racecar drivers, there is no point.

Just use the best fuel regularly available in your country, that's what it's tuned for.

 

If it's ethanol free 100 I'd say you may notice a difference if your normal fuel is 91-92 with ethanol. If not it's probably a defective sensor in your "butt dyno".

Interestingly some of the import tuners are getting really good performance tuning cars to use E85. Totally different issue but it's interesting.

 

You will notice a huge impact. Mostly psychological and financial. You will notice no material difference in street driving...

 

I believe there is such a discrepancy in E-85 that you can't rely on it being consistent enough to tune based on this fuel. In the colder months E-85 has a higher percentage of gasoline, because ethanol doesn't light off as well in cold temps.

 

+1 with Entropy. Excellent post.

 

Unless the engine has the compression to use the extra octane, you will end up making LESS HP on higher octane.

Compression can be mechanical (compression ratio), pressurized intake (turbo, super), or ignition (advance). But you have to have it, or the octane does not make power, but subtracts power, albeit tiny amounts.

 

One thing that I forgot to add is that the premium octane that I use is always ethanol free. The nice thing about Colorado is we have a few places that sell ethanol free premium octane right at the pump. I'm sure a fair amount of other states have this too.

 

The F40 is a great example of a high strung mechanical engine AND forced induction, and- if you'll permit me saying this - an absence of the modern ECU and sensor capabilities. Higher octane in that situation should allow you to run more consistently at a high level

 

Of course I'll permit you to say that because you're correct. The difference is somewhat subtle though, and basically undetectable after 98 octane, which is probably the equivalent of 102 at sea level.

 

False.

E-85 is amazing. I've had a stock motor 4 cyl, running 485hp for two years issue free. Far from the only person with those results.

E-85 > 100 octane

$1.85 gal > $7+

All day long. You just need the injectors, and pump to handle higher power.

 

Yes it is a good fuel but he is correct, the alcohol content varies at the pump.

Only way to do this correctly is to install a fuel composition sensor so the ecu can adjust for alcohol percentage in real time. Not possible on all vehicles however.

You may be tuned on E85 and no composition sensor but your air fuel ratio is changing if it's say 65% alcohol vs 85% alcohol.

 

Mark

What's important as to whether or not it makes a difference, hinges on a few things.

Actual octane of the fuel in the pumps and the density.

A problem in the US is poor quality fuel and the octane rating system. What you want in a car like your F12 or my 458, is a fuel with a high Motor Octane Number (MON). As you probably know, the US uses the AKI. This is the average of the Research Octane Number (RON) and MON. RON and MON is basically just two different ways of measuring when the fuel combust due to compression. However, the MON is more stringent. The problem with the AKI index is, that there's basically no rules as to how low the MON can be. There are some basic limitations, but the difference can be significant. This means that you can buy a 93 AKI that is quite crappy under high load conditions. It works fine when putting it in a low compression V8 in a Yukon, but it's worthless in an application such as ours and other modern forced induction engines like the VW TSI power plants etc.

I have a friend who's been working in the US oil industry as a chemical engineer for over 20 years, and what he claim is that it's not uncommon to get a 93 in the US with a RON of 101 and a MON of 85. That is a horrible fuel for anything but the soccermom cruiser. Add to that fuel that loses it's octane rating faster than ever.

What he also tells me is that the density has gone down. A density of 820 g pr. l is not uncommon either. So if you get fuel with a density of 820 g/l rather than 830 g/l, you get less energy density per cc of fuel the injectors delivers.

One of the advantages we have here in Europe with using the RON system is, that the fuel needs a decent MON number to work in any case. If the MON number for our 99 was as low as the MON of 85 I used in my example, it would never work in any car set up for it. This means our 99 RON quality fuels such as Shell 99 V-Power usually has a MON number of about 91. So that equates to a 95 AKI fuel. a proper 91 AKI should have a MON of 87 and a RON of 95. This is the case for just about all quality fuel sold in Europe and it's the most common. This is also what Ferrari test their cars on when they use Shell 95.

Our cars were set up to perform at their best using what is available. In the case of Ferrari, that's Shell V-Power. This means they map the car to run just about max on 95 and you may get a bit extra on the 99. This fits very well with my personal experience. What difference I find using regular Shell 95 and V-Power 99 is very subtle. It's not so much about power, as a feeling of slightly better response and slightly better millage. I've tried the 100 AKI and there was absolutely no difference between that an 99 V-Power other than a bit more pops in the exhaust and the car ran slightly hotter. I don't doubt that if one lives in US states like California which ar notorious for poor quality fuel, you can feel a difference. While I don't know a lot about the fuel in Florida, I've been told it's not the best either. If you run ethanol fuels like E10 or E15, everything just gets worse as the energy density drops even further.

A qualified guess is that you feel a difference because the fuel where you are, is not up to spec. In your case, I'd do the following. Instead of wasting a bunch of money filling up with 100 AKI which the engine can never use, try and see where the balance is. Fill your tank 90% with 93 and 10% with 100 AKI then work your way down from there till you reach a point where it makes no difference. In other words. simply use the 100 AKI as a "proper" octane booster rather than the crappy over-the-counter stuff.

In terms of lubrication, race fuels are also different. Many racers and engine builders will tell you that they sometimes add a tiny bit of oil to a tank of fuel. I've seen this done a lot in applications where engines are abused about as hard as engines can be - namely the use of high octane fuels in offshore powerboats. Of course that's a bit apples and oranges, but as far as wear goes, it's still worth considering that the 100 AKI is thinner and a "dryer" fuel than the 91-93 AKI street fuels. The fuel also have a lubricating effect on certain parts.

A last little thing to add is this. If the fuel burn in the exhaust rather than the combustion chamber, it goes without saying that it does not burn where it makes the power. One thing I noticed after running 100 AKI was that my exhaust was more sooty and it popped more. This means a less complete an clean burn. Again, not optimum power is made from the fuel.

If you want to use 100 AKI, take the car to a proper race shop and have the ECU re-calibrated for it. Just be aware that your warranty will be gone and you'll be stuck on 100 AKI.

Glad to see you enjoy that beautiful car of yours

 

Just for the record, David is correct.

Both gasoline and ethanol have seasonal blends due to the ambient temperature. There is an E-85 blend in the summer, E-80 in spring, and E-75 in winter. The pump label remains "E-85" all year long. As David stated, the increased 20 to 25 percent gasoline composition level (versus 15 percent) is for starting purposes.

Source: (see page 18, Volatility Class by State by Month)
http://www.ethanolretailer.com/images/uploads/Ethanol_Retailer.pdf

However, this is not to preclude a jobber from blending a constant E-85 custom blend for a customer (like racers) all year long providing it is not put into public fueling facilities as "on spec" product during other seasons.

 

Or Chevron.
Perhaps Exxon/Mobil in a pinch.

 

Absolutely true.

A friend of mine sells Sunoco 100 and he uses it in his vintage cars and small engines. He discovered that it is great for storage, because of the high quality it does not varnish or gum up.