Jatmobil

Audi manuals, and even the inside of the fuel door has a label that says to use 95 RON. RON is "Research Octane Number" and a method used by Europe to measure Octane (How well a fuel performs under load at the 600 rpm range). Another method is the MON, same as RON, but in the 900 rpm range and is considred a better measure of fuel performance.

In the US we use the AKI rating (Anti Knock Index) or sometimes also referred to as (R+M)/2 which is nothing but the average of the RON and MON that I mentioned above. So, a 95 RON translates to 91 AKI or 91 (R+M)/2.

So to make the long story short, Audi recommends 95RON, which is 91 AKI and that is what I use!

RobC

The engine was tuned to run on 91+ octane ([R+M]/2). You can use lower octane in emergencies if higher octanes are not available, but I would not do that on a long term basis. Yes the engine should be able to detect knock and retard timing, but you've likely lost any design margin and you potentially could get some knock in situations of extreme temperatures, load, etc.

My analogy is a real experience in a mountain drive where a BMW driver was relying on the car's stability control to keep him in check, allowing him to drive beyond his ability at times. If you do this too much, eventually the built-in protection will not be able to correct for your mistakes, resulting in a crash.

jdkinzenbaw

Cool. Very helpful information. Clearly I have a lot to learn.

I always buy premium for my gas vehicles (just not the diesels!). It seems to make my '09 Chevy Impala happier and I suppose helps prevent knocking as well.

Like somebody else here said... now that fuel is over $3.00/gallon, 20 cents difference is a pretty small percentage overall, one I can certainly afford if it means less trips in for repair.

mikem33

The a6 (3.0T) should have no issues running on regular; the owner manual points out that 'a small loss of performance' is the price paid for it.

My previous car (M56) in contrast, warned in the users manual that if premium could not be found, one was to add no more than 1/4 tank of regular, avoid fast acceleration, uphills, or anything that made the car work, and fill the rest of the tank with premium as soon as humanly possible.

I previously had a Jaguar XF supercharged; it also allowed regular with slight performance loss. I ran regular on it a couple of times and could not feel any difference, nor measure any consistent or significant difference on 0-60 runs. (Significant for me is more than 2/10ths; less than that is in the noise).

All this means in the real world is that the A6 has a computer that can adjust far enough to prevent detonation with regular, while the M56 (probably) could not.

A lot of this is to make cars 'feel' premium, even if the gas costs more.
A VW with the same engine probably would be specified with regular.

Look, for instance, at a 2008 Nissan Armada vs. a 2008 Infiniti QX56.
Once requires premium, one uses regular. Exact same engine. Performance penalty is about 5 lb/ft (out of 390) and 3 HP (out of 320). I'm not even sure if the computer tuning is different or not. But I guess owners of Infinitis want to feel their car is premium and pay accordingly. For the record... the armada is lighter, and faster.

So, technically speaking, Audi is OK with running regular on this engine, per their user manual and some training material I've seen out in the web on the 3.0T engine. Having said that, most folks think it's not worth the risk over the 5% delta in gas price; to me, that's an individual decision.

It's unclear what the performance loss is in the audi; it will most likely be imperceptible in any conditions other than full throttle (and maybe even then). On the flip side, the annual difference is less than $200 to run premium, even assuming no change in fuel economy. The risk/benefit here is for each to decide. Car and Driver had an article long ago that seemed to imply that the change in cost was offset by the decrease in fuel economy.
Here's an experiment waiting to happen......

You could always ask Audi, but to get a real answer you need to ask AoA and not the dealer, and you need to ask in writing. Verbal 'you should do that' from the service guy don't count in my book.

Mike

mnsnwbrdr

I have filled my RS6 several times with regular where I couldn't find premium (Wisconsin, I love you, but you hate my German car) - always noting worse fuel economy (1-2 mpg highway). Never done it to our Q5 so I don't have statistics on a newer engine.

Skimping on premium is not worth it to me. In fact, I try to do 93 as much as possible - my neighborhood station went back to 92 recently so I have to look around again ...

audi40

Might want to read this:

http://www.consumerenergycenter.org/...s_premium.html

Metallic-Force

I really have to disagree with this, when I had the Mustang, my car takes off much smoother with higher octane. A friend of mine even mixed it with 100 octane and feels like a dream.

BugeyeRX

I disagree as well.

mikem33

Hi,

I think the discussion should really be constrained to "can I used regular on a C7 A6 3.0T" or something to that effect; this topic is too complex otherwise!

I don't think there's any doubt that higher octane gas has different characteristics than lower octane gas, or that detonation will occur with lower octane gas in certain engines. A particular engine's timing flexibility, compression ratio, ECU programming, amount of boost, etc., are all factors that play a part.

In the particular case of the 3.0T engine, it seems to me that Audi has programmed the ECU to properly adapt to standard pump grade by sacrificing a few horsepower without any detonation; hence, the manual explicitly allows the use of 87 octane with some performance loss but no other effect. Since the loss is unspecified, it may be something that drivers can feel, or maybe not even perceptible. There are some cars that are very unhappy when they run on anything below 91; this one does not seem to be one of them.

Altitude and temperature also have a significant effect on the onset of detonation; at higher altitude, it's less of an issue than at sea level.

Having said all that, I use premium given that the cost difference is really not that big of a deal, and I want every HP I can get. But I would feel perfectly comfortable putting regular on this car if for some reason I couldn't find premium, or if premium is suddenly a buck more than regular.

stoulana

We have few stations in Canada that offer 94 Octane & almost all offer 92,I sometimes fill my A6 with 94 but I never go to 87. Once added 87 to my 2nd car BMW 535i (2009) & check engine light came on next day. Some of fuel pump issues were blamed on octane level but seems A6 is more forgiving, other cars are not.