I was so low on fuel that I had no other choice, because the gas station was out of premium. The good news is, the engine doesn't knock and runs just fine. The bad news is, fuel consumption has almost doubled. I'm glad it's only half a tank. I guess I'll just fill her up with 91 (Can't find 93 'round here).

Unocal race fuel (100 octane) and 11 gallons of premium (91 octane here in SoCal), my A4 really came alive.

Bob K.

Being all the time in Germany and all, I'm sure you know the "Yellow Angels." Anyway, according to them the 100 Octane fuel is a complete rip-off. Porsche agreed, too. I've heard some people swear they get better performance and/or better mileage with that juice. Now, I guess it depends all on the engine. I just want 93 Octane, damn it! :-P

But the price! There's always the toluene option, right? Well, I don't feel like pouring a solvent in my gas tank. I'm afraid of brain damage, too. "Too late," you say? Probably! ;-)

And while my S4 LOVES the 105 my 1.8T A4 doesn't and neither does my 2.8 12V. Actually the 1.8T prefers a mixture with 91 octane to achieve 97 octane but the 2.8 12V hates anything over 94 or so and is markedly slower with pure 105. A closer-to-seal level car might like an additional 1% increase in octane to around 95 but any more is a waste of money. Our ECU cant advance timing to take advantage of higher octane ratings so any higher is a waste of money and perfectly good fuel for us.

So I keep 20 or so gallons around at all times in 5 gal containers but other than the S4 only use it to mix with my Shell 91 octane pump gas when I need a little boost in the octane.

I never buy the 100 octane due to it costing the same as 105 and since I mostly mix to a desired ratio the 105 is the better bargain but still spendy at $4.75 per gallon.

Always a little scarey driving home with 4 or 5 five gallon containers of 105 gasoline in the trunk and back seat tho. I LIVE in the rearview mirror for that drive and take ALL backroad/neighborhood streets!!

My car and a lot of others i know love this stuff, there is a definate improvement when i'm using it and it seems that the car appreciates it more after 1 or 2 tankfulls. I'll put a quarter of half tank of this 100 octane stuff in and see how it goes first. It shouldn't damage anything though should it?

You can always use octane booster if you want.

just been on the shell Optimax website and even though they won't give the exact octane level they do say it's somewhere between 98 and 99.....i've used it for about 5-6 months on and off now with nothing but positive results, even better MPG, but not offset against the extra cost though.
It's basically just a reinvention of what the UK call 'Super' unleaded and what you guys call 'Premium'....i think anyway.....i'll shut up now! ; )

It basically breaks down overly long fuel molecules and combines the short fuel molecules to help combustion.

Overly long fuel molecules do not burn in the short time allowed in the combustion cycle due to their length.

Short fuel molecules pre-ignite, because they burn too easily (like lower octane fuel--lots of shorter fuel molecules).

For higher performance (higher-compression and higher-octane) engines like ours, it makes sense to use a fuel catalyst to reduce the numbers of short and long fuel molecules to improve combustion.

Having run the Fitch Fuel Catalyst for about two years, I can say that you will not feel much of a performance gain if you regularly use premium fuel. However, on those occasions where I have had to fill-up on the lower octane fuel, it makes a big difference--I can feel that the engine runs better after allowing the fuel catalyst a few hours to work on the low octane fuel than it runs immediately after fill-up with low octane fuel. I find it gives me piece of mind living in California where our fuel regulators require petroleum refiners to add so much crap to our fuel and prevent them from offering higher octane fuels.

For those who do not know, in CA, refiners may offer up to 91--not 92 to 99--and 100 octane fuels with the 100 octane fuel designated as "race fuel" and insanely taxed). Union76 was the last refiner to try to fight for keeping 92 octane and the CA regulators forced them to water-down the fuel and put 91 octane stickers over the 92 octane pumps they had used for years. Industry pressure remains to offer something above 91 octane, but the regulators have held their ground despite the consumer's demands for reasonably priced higher octane fuel--like 93.

I have used the cheapest fuel at Arco (87) in my 12v and it doesn't seem to produce pinging.
93 has been discontinued and only 91 is available here in California.

I wasn't too surprised that I got no pinging. I mean, even 87 (Pump Octane) still has the required 87 AKI. But the fuel consumption shocked me!

The ethanol seems to reduce mileage, too, so I wonder if we really produce less emissions despite burning more fuel.

Where do yo get this Fitch fuel catalyst?

... which is still higher Octane than the commonly available premium gas in the US, but it's way less than "race gas."

You Texans doen't know what we have to deal with here in California! ;-)

PS: Octane boosters like to foul spark plugs...

You should get one of those self-sealing rubber bladder fuel tanks the military uses. Maybe Missile Man 120 got one that you can borrow. ;-)

- In the US Octane is defined by PON***
- In Germany Octane is defined by RON* (ROZ)
- I don't know about the UK, but I think they go by RON,* just like Aussies


That means you have to convert Octane ratings to compare them.


RON* - MON - PON (also Road Octane Number**) = AKI
90 --> 83 --> 86.6 Regular
92 --> 85 --> 88.5 Plus
95 --> 87 --> 91 Premium
96 --> 88 --> 92
98 --> 90 --> 94
100 -->91.5 -->95.8
105 -->95 --> 100
110 -->99 --> 104.5

87-90 AKI = Regular
91-96 AKI = Premium

Minimum requirement for '96 2.8 Audi:
87AKI or 91 RON


*RON = Research Octane Number = ROZ (Research Octane Zahl)
**RON = Road Octane Number

----> RON/ROZ is not the same as RON!!!

***PON = Pump Octane Number= (Research Octane Numer+Motor Octane Numer):2

PON=AKI (Anti Knock Index)

Since February, my milage = 16-18 until I had a bored TB, CAI & VS put on and the last 2 tanks = 13.
I am enjoying the new TB, CAI & VS with more revs in the higher ranges. If I can keep my foot out of it, I may get better milage. I have been running 87 since around February.
The mods have decreased my milage, not the octane.

Unless I drive like Nicki Lauda. ;-)

The MTBE ended up in the ground water due to leaking tanks at gas stations. Bon appetit! :-x

Less octane than you guys and we still pay twice the price!

93 seems to be the highest commonly available fuel here in the US (I'm not counting race gas). And most of us in California are stuck with 91. So you guys in Europe and the UK can get higher Octane fuel. But yeah, the price... :-0

Most people get 93 or 96. You can also get 98. Wouldn't 93 octane have better emissions and create better gas mileage than 91. Is there a reason for it? CA is so obsessed...