I'm running a supercharger on my 07 4.3L engine. It is recommended that I burn at least 91 octane with it. I'm currently using 92 octane because of its availability. I am able to find 90 octane and was wondering if that grade would make that much of difference? I'm contemplating letting my tank (34 gal.) get down to about 1/4 full and filling up to the 1/2 mark or less with the 90 octane to see how it runs. If the engine "knocks" then I can fillup the rest of the way with 92 octane. I'd appreciate your comments and assistance.