Marty

The S4 owner's manual states that "The fuel recommended for your vehicle is unleaded premium grade gas with a minimum octane rating of 91AKI/95RON or higher". It also states that you shouldn't use any fuel lower than 91RON, otherwise expensive engine damage will occur. The fuel filler door label also states minimum of 95RON. This seems to limit you to Sunoco. Comments?

AvramD

As I recall, there are two different ways of measuring octane, one is Research Octane Number. I don't remember what the other one is called. The pump octane number is the average of the two. Assuming that AKI is the other one, we're looking at 93 octane or better. Texaco, Exxon, Mobile, Citgo, etc all have 93.

Sandy

91 is the highest I've ever seen in Denver

scot kight

Research octane number and mechanical octane number.

RON is used in europe and is higher then MON. In america they use (RON+MON)/2 When you look on the pump you will see that somewhere.

Generally mon is about 4 points lower then RON. So a RON of 95 and a MON of 91 come out as a (RON+MON)/2 of 93.

Therefor 93 is just fine. the 94 is signifigantly more expensive and wont add any benifit. Suggestion though, find a good gas station and stick with it. Bad gas can be really really bad for your car... Esp with turbos and 250+hp. Even with knock sensors, you cant make it 100% resistant to bad low octane gas.

AvramD

I'm not sure exactly how this plays out, but I believe you get the same gas we do down at sea level, it's just that they have to measure it by how it rates *at that altitude.* What is "regular unleaded" rated at there? At sea level, it's 87.

ErikR

The distributors have different packages that are blended to get different octane and detergencies. At high elevations the octane requirements are lower for a given engine. So, in Den/SLC 91 is equi. to 93. You can get 93 in Silverthorn as I remember.

My T knocks with 91 from one company, even with octane boost, and no knock from another. So the blends do vary. The only way to hear the knock is to accelerate with the windows open!!!!.

Sandy

Never use regular so I'll have to check

Reggie

It's 85 here in CO - BTW I never use it either

Reed M

Octane for all grades of gas is lower at higher altitudes because of the lower barometric pressure. 91 at altitude is equivalent to 93 at sea level because you don't need the same anti-knock levels in the mountains (87 is equivanlent to 89, etc.).

A friend of mine at Conoco explained it all to me years ago (in technical terms, though). Just remember to put the best Super Unleaded you can buy in it. For those of you lucky enough to be able to buy Sunoco gas, I believe they have a 94 octane Super. Remember, the more octane, the happier your engine will be (and the more power it can make)!

Paul Allen

I asked Sunoco about this. The bottom line is, the US rating is an average of two different ratings (different ways to measure the octane of a fuel), that are about 9-10 points apart.

Sunoco Ultra 94 is 89 Motor rating, 99 Research rating (RON=Research Octane Number), so the US rating is the average, or (89+99)/2 = 94.

So 95RON is THE SAME as a 91 US rating.

Bottom line is, any US premium gas will be ok.