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Re: Octane Rating (archive)
[ Follow Ups ] [ 5-series (E34) Message Board ] [ Msg. Board FAQ ]
Posted by Mike on January 07, 2001 at 22:51:16:

In Reply to: Octane Rating posted by Ghassan Shaheeb on January 07, 2001 at 20:01:28:


Hi,
Does anyone know why BMW insists on uning high octane grade fuel (to be precise 91 Octane) when in fact engines like the ones on E34 535i and 525i employ a compression ration of 9.5:1?

Isn't it 87 or 89 octane should be sufficient for this compression ratio?

Please explain me this mystery.

1990 535iM.
Thank you.

I run midgrade (88 octane) in both my '92 535ia and my '99 528ia and they both do great - lots of power when I need it and good gas mileage to boot. My local BMW dealer service man gave me the suggestion. I had been running premium in both, but they don't seem to need it. The car spends all of its city time between 5000 and 6500 feet altitude. I haven't tried regular grade, but the 535i should be able to handle it because it's a relatively low compression ratio engine (9).


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