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  1. #1

    Default 90 vs. 91 Octane

    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.

  2. #2
    stephan's Avatar
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    Sep 2010
    Far West, Oregon USA,
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    It depends on what your effective compression ratio is when your SC is runnin full tilt. The manufacturer would know this better than anyone, so I'd say stay with what they recommend. Are you running the stock cogs they supplied with it, or are you over or underdriving it? If you're underdriving it, then you might be able to get by with lower octane but I would still ask them to be on the safe side.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol

  3. #3


    Thanks. I running the stock cogs. When I was looking at buying the S/C I had underdrivve pulleys. The advised that I must take them off.

  4. #4


    Also depends if you lug or really get on it waay hard. Those two conditions can induce knocking that will harm you motor.

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