Test drove an M3 SMG last night,
 

and I beat on it for quite a bit so we started to run out of gas. So whether it was the nice guy in me or the speed freak who wanted to keep pushing this thing to the limit, I offered to gas it up for him. So I went in and paid and he filled it up. When I came back outside I saw he was using 87 regular octane... I didn't really say much, but he said that's all it needed. I know this is an Audi forum, and I drive an A4, but my question is: How can I figure out what octane is required by the compression ratio and what does it mean?

minimum octane depends on a variety of factors... ambient temp/humidity, engine compression ratios,
 

is the car force inducted, what is the max timing possible? what is the plugs being used in the car...

basically the reason for using higher octane fuels is to reduce/eliminate the chance of the engine pre-detonating(bad thing). anytime you increase engine compression, add boost, or run hotter plugs you generally will need to increase the octane rating of the fuel you're using.

M3 requires premium - your friend is using the wrong fuel.

OMFG what an idiot. How do people like that get an M3? Trust fund?

Re: M3 requires premium - your friend is using the wrong fuel.
 

Thats what I thought too, but he was a used car dealer I went to, don't think he knew. I was telling HIM stuff about the car he didn't even know....

knock sensors are a wonderful thing.........

Ah the truth comes out. He was a car salesman. Well there you have it.

87 oct. OUCH...

Re: OMFG what an idiot. How do people like that get an M3? Trust fund?
 

He was just an oblivious salesman

Re: minimum octane depends on a variety of factors... ambient temp/humidity, engine compression
 

So I guess you can't just base it on the compression ration then, thanks.