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BMW say that we should use 98 ROZ and that lower octane reduce power and milage.

But how much reduction is there in reality when using fex. 95 (ROZ) ?

Is it bad for the engine to switch between 98 and 95 (often gas stations don't have 98)

Anybody knows ?

/Michael
 

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ratemut said:
Is it bad for the engine to switch between 98 and 95 (often gas stations don't have 98)l
No. More than half of my 35' km I was driving with 95 octane gas (couldn't get 98). No problem. However, I would not go with 92 exept for a few miles and then fill up wit 95/98 at the next gas station.

Manfred
 

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The knock sensors in the engine will adjust ignition timing and other variables to compensate for lower octane fuel. I don't know what the ECU does to sense and fully utilise high octane fuel but the knock sensors deal with low octane / engine pre detonation.
 

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I've been running 93 in my S without problems. However, I suspect that mixing of gasoline brands is the culprit for intermittent throttle twitchiness - that lightswitch feeling of on or off that it sometimes gets.
 

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Lenz said:
The knock sensors in the engine will adjust ignition timing and other variables to compensate for lower octane fuel. I don't know what the ECU does to sense and fully utilise high octane fuel but the knock sensors deal with low octane / engine pre detonation.
Typically the knock sensors "microphones" are monitored by the ECU, which advances timing (giving more hp) until engine knock. Since lower octane fuel knocks earlier, the ECU hears this and retards timing which cuts hp a little. On the BMW e46 M3 each cylinder has its own knock sensor microphone. Regular cars often have just one or two. Don't know about the K1200S.
 
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