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  1. #1
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    So if all of the 78-79 235 heads are gone..

    Hi guys, new member here. Have been browsing this forum for years as a guest, and it is a fantastic resource and great community.

    Been on the lookout for the 323872/873 heads to do a head swap on my GT150 (J150STLCEM), but have not had any luck.

    My questions are, if I cant get ahold of the 872/873heads:

    1-> What is the next best (smallest cc) head for the crossflow v6?

    2-> I have the 322544/545 heads on the motor now. If I was to mill my stock heads, what is the minimum piston to head clearance that can be ran safely?

    Also, is there an OMC casting number guide out there anywhere by chance? I do look through the diagrams on the parts sites, but looking for more in depth info on the parts.

    Thank you in advance.

  2. #2
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    If you have a GT then you have the next best heads. Take them down by hand on a thick piece of glass with 120 grit sand paper taped to the glass. To be sure they don't hit,install the head without a gasket,loose bolts, spin the crank. if they don't hit you are good to go.. You should be able to get 125-135 psi by doing this. You can also look for a set of land and sea high comp heads but you will need to run 96-98 octane.

    I think you can go .010-.015 before they hit,if you want to start there.
    Last edited by perfmarine1; 09-25-2021 at 08:11 AM.

  3. #3
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    With some digging you can probably still find these heads because when the crossflows blow (more a matter of "when" not "if"), people often don't fix them anymore - just part them out. Try some of the OMC Facebook groups.

    Matt

  4. #4
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    1. Bests heads after the 78/9 235 are IMO the 76/7 200 then 78-82 200 and then what you have.
    2. Minimum IMO is .041 and you have to maintain that in ALL areas including the intake edge of the piston dome.

    No matter which ones you go with if you add compression you will need to reduce timing, run better fuel and possibly rejet carbs and the heavier boat you push the more critical to maintain engine life.

  5. #5
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    I have some 235 heads but they are cut for high comp and need some welding. Anyone interested please PM me.
    Last edited by rjdubiel; 09-30-2021 at 02:16 PM.
    1973 Viper
    1978 Viking

  6. #6
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    Always wondered if you take a couple degrees of timing out, wouldn't that nearly negate the power advantage ?

  7. #7
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    Quote Originally Posted by Revenge22 View Post
    Always wondered if you take a couple degrees of timing out, wouldn't that nearly negate the power advantage ?
    Absolutely not.

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