Quote:
Originally Posted by regular guy
Here's what's lacking for me in this discussion of detonation. Are we ready to admit that BMW screwed up the ECU programming if they can't handle 91 octane US gas. Yet in spite of five years to fix it...they couldn't? Are we ready to say they're that incompetent? I don't believe that, which is why I don't believe detonation on NA engines is a likely cause.
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Why would BMW even be paying attemption? Overall failure rates are still very low for non S/C cars. I think most manufacturers would be pretty happy with a .5 - 1% failure rate of a high performance engine. Saying there's a possible connection between octane and failure does not equate to "BMW screwed up their ECU programming".
Lets put it this way. Suppose someone told you that with statistical significance, we know that drinking increases your risk of dying from a particular disease from 1 in a million to 2 in a million -- a 100% increase in risk. Would you stop drinking? Probably not -- we are still talking pretty low probability of death. It doesn't in any way diminish alcohols value in this case as a powerful explanatory value, but it also doesn't put alcohol on the level of cyanide. Now lets suppose someone tells you that drinking increases your risk of dying from another disease from 1/10 to 1/8, a 25% increase in risk. Would you stop? Probably, I know I would (or at least cut back). In statistics, knowing something might be explanatory is useful, but not that valuable without understanding the context, and particularly without having some idea of whether it's also causative. It is definitely also possible, as you suggest, that octane is correlated but not causative, because people in the lower octane states also do other things that are bad for engines.
An finally, I'm also not sure why the conclusion that lower octane is related to the failures necessary equates to BMW screwup. I have a somewhat strong suspicion that many of the CA failures might have also been tuned, so it could very well be the case that BMW got the ECU programming right for 91 octane, but the aftermarket tunes have not.