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what gas to use?

Discussion in 'Boats and Motors' started by Rik, Mar 25, 2008.

  1. Rik

    Rik "King Fish"

    I just bought a 77 thompson with a 302 I/O,looking for opinions on what gas to use?Should I use the higher octanes?
     
  2. I'm no mechanic, but have been told by more than one that you won't really get any benefit from running the higher octanes, unless you're running a motor with higher compression (like a high performance motor with 12:1 pistons or something). These engines were made to run on the lower octane fuels.

    Something you might consider for a motor of that age is a lead additive. My old man (right or wrong) used to go out of his way to run leaded in his 85 inboard big block. And that big ol motor ran very well and was super dependable with 3,000 + hours on it.
     

  3. I always run at least 89 oct. in these older motors.
     
  4. You only need higher octane if she knocks. You should find out if this year had hardened valve seats. (probably does). If not you should to add a lead substitute.
     
  5. Just be sure you avoid any gas that contains ethanol.
     
  6. Good luck with that.