JCL- thank you for all the constructive feedback. And so I think one pressing question -- and one lesser question! -- remains:

(1) Why does our fuel door say "91 MINIMUM?"

(2) Same logic for my Dad's C4S then too, right? Don't bother with 100?

Another note: I know for a fact that, as someone mentioned earlier, turbo- or supercharged engines necessarily DO benefit from higher octane fuel. Apparently the Mitsu Evo is a RADICALLY different beast when running on 100 octane fuel.

And finally: as I mentioned earlier, 91 octane fuel *DOES* produce *SOME* knocking at low RPMs under more than 1/4-throttle position. Any thoughts?

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MARC/CROSVS | UCLA Bruin, B.A. Econ, Aug 2004 | J.D., Thomas Jefferson School of Law, May 2008 -- MEMBER: California State Bar, December 4, 2008

2005 BMW 645 Cabrio | Black Sapphire Metallic, Ti trim | 6AT | fully loaded sans HUD

2000 Ford Mustang V6 | laser red on tan | 5-spd | track-prepped