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Technical Need information on Offenhauser "350" heads

Discussion in 'The Hokey Ass Message Board' started by wheeldog57, Jan 7, 2020.

  1. wheeldog57
    Joined: Dec 6, 2013
    Posts: 3,182

    wheeldog57
    Member

    I picked up a set of heads yesterday ( thanks Stephen) They are Offenhauser aluminium 24 stud, center hose outlet, finned heads.
    They have a couple stampings on each head.
    I forget the prefix, but they have a "350"
    I am at work now and heads safely stored in the garage at home so no pictures until later.
    Anyway, I did a little research and I found "400' and "425" heads for sale but no "350" heads. What does the "350" mean?
     
  2. flathead4d
    Joined: Oct 24, 2005
    Posts: 898

    flathead4d
    Member

    It's the compression ratio of the heads. I'll check and find out what ratio that is.
     
  3. Black Panther
    Joined: Jan 6, 2010
    Posts: 2,133

    Black Panther
    Member
    from SoCal

    The 350, 400 and 425 are probably for what lift cam theyll accommodate...they're probably for near stock motors with smaller cams..
     
    Speed Gems likes this.
  4. wheeldog57
    Joined: Dec 6, 2013
    Posts: 3,182

    wheeldog57
    Member

    These are the heads. . . 20200107_172208.jpg
    And here are the stampings, cant really make out the first part 20200107_172427.jpg
     
    VANDENPLAS likes this.

  5. flathead4d
    Joined: Oct 24, 2005
    Posts: 898

    flathead4d
    Member

    Offey heads are marked 325 350 375 400 and 425. A 325 head is the highest compression ratio and a 425 head marking is the lowest. Your 350 head compression ratio depends on your bore and stroke. Example: If you have a
    3-1/16 bore and a 3-3/4 stroke your compression ratio is 9.0
    I have a 3-3/8 bore and a 4 inch stroke (Mercury crankshaft) and my 350 heads are 10.7 CR. Hope this gives you some idea of what you have.
     
    stillrunners and wheeldog57 like this.
  6. tubman
    Joined: May 16, 2007
    Posts: 6,916

    tubman
    ALLIANCE MEMBER

    "OECO" - "Offenhauser Equipment Company"? It also goes without saying that those heads have obviously been used and therefore may have been resurfaced at one time, so all bets are off on the "350" and they should be checked before use.
     
  7. wheeldog57
    Joined: Dec 6, 2013
    Posts: 3,182

    wheeldog57
    Member

    Thanks alot guys.
     
  8. dan c
    Joined: Jan 30, 2012
    Posts: 2,520

    dan c
    ALLIANCE MEMBER

    it's the measurement of the top of the valve pocket. a stock iron head is .375" so yours should be .350". more compression and would have to be used with a low-lift cam.
     
  9. tubman
    Joined: May 16, 2007
    Posts: 6,916

    tubman
    ALLIANCE MEMBER

    Lift on a stock 8BA cam is .330; that .350 doesn't leave much room for anything aftermarket (assuming that early cams have similar lift). Sounds like what you need for a "low end" hop-up (heads, carbs, and ignition with a stock cam).
     
  10. Stephen Barrett
    Joined: Sep 24, 2019
    Posts: 777

    Stephen Barrett
    Member

    The motor they came off had a 4"stroke mercury crank and was bored .30 over it also had an Isky 3/4 cam. Hope that helps. Without measuring that's all I know. You're welcome to come by anytime to measure things if you'd like. Also the offer still stands if you have any interest in the motor. Good luck and let me know if you need anything. Take care.
     

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