E39 540i, use 89 octane in the meantime?

[Laszlo Vecsey <master@xxxxxxxxxxxxxx>]

Since the BMW engines are supposedly tuned for 89 octane or so, am I
better off running with that level octane to get the most power? And save
a little cash on fuel in the meantime, I'll be doing the JimC upgrade when
its available and resuming to high octane (93 and 94). Seems to me I'm
better off using 89 now, even though the owners manual says to use high
test.. comments? i.e. I should get more power and better fuel economy now
by dropping down to 89, since my chip has yet to be reprogrammed.

- - lv

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