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  1. #1
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    2.7 heads on 3.0

    I have heard many times about using 2.7 heads on 3.0 motors to increase compression ratio. I believe the 200 & 225 from 1986 & 87 are 2.7's. Are there any other 2.7's? I have seen different part numbers for 2.7 heads. Are they all the same? My 1997 225 Venom has lower comp in the two bottom cyls. Are the 2.7 heads made with equal chambers or are they also made with bigger chambers for the bottom cylinders? I would like to get some 2.7 heads, but I'm not sure what to look for.... Also, safest way to plug the relief holes in the liners? I'm thinking some kind of epoxy would be the safest (and easiest) way to go. Anybody with experience with epoxying the relief holes? What brand and type to use?

    Hal
    Hal

    "Ton o' metalflake" 1982 Concord Mach II with 1997 Johnson 225 Venom

  2. #2
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    Your venom has larger chambers in the bottom cyls to decrease compression. On the older motors they just jetted the bottom carbs up 2 sizes instead of making the bottom chambers higher.

    People have drilled and tapped for brass plugs. I have always clean the holes well and pushed some epoxy through them never had a problem.

    Kevin
    Quartershot T-3R 15" 3.5L E-Tec 1.62 Sportmaster


  3. #3
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    I have 2.7 heads on my 3.0 Looper. If I remember right, it raised the compression from stock (around 85-90psi) to around 100-105PSI. I was going to plug the relief holes in my liners, but I was told that it would bump the compression up to around 120psi...which was pushing the limits for pump gas.

    Just something to check into before you do it.

    Hopefully some of the OMC guru's on here can shed some light on that.
    Ian

    ...boatless for now.

  4. #4
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    Two versions one has a chamber deapth of .675 and the other .700 the 700 came on the 225 and the 675 on 200XP/GT engines

  5. #5
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    We usually keep them around 135-140 but have run 150 on pump with no issues. I dont recommend testing the limits
    Quartershot T-3R 15" 3.5L E-Tec 1.62 Sportmaster


  6. #6
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    Thanks for the answers guys!
    I have been looking in the parts diagrams for '86 & '87 200 & 225 motors and found the numbers 0398268 & 0398269. I suppose the latter are the 200XP/GT heads. I have also seen the number 331490 here on the forum and on e-bay listings, but I have not found that number in the diagrams.... Anybody knows for sure where 331490 heads come from?

    I suppose bigger main jets are in order with higher comp. Two sizes up on the top four holes and four sizes up on the bottom two?

    Thanks again
    Hal
    Hal

    "Ton o' metalflake" 1982 Concord Mach II with 1997 Johnson 225 Venom

  7. #7
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    86 & 87 2.7s. BTW I was under the impression the dash # at the end of 331490-1, -2 or -3 refereed to chamber depth but it does not.
    Quartershot T-3R 15" 3.5L E-Tec 1.62 Sportmaster


  8. #8
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    OK. Purchased a set of 331490 heads on e-bay for $150. I will blame you if they don't fit...

    I hope someday my motor will be able to turn that 26" Raker II prop up to 5500rpm or so. It will probably require some setback & tuning for the motor and some dieting for the owner....

    Thanks again
    Hal
    Hal

    "Ton o' metalflake" 1982 Concord Mach II with 1997 Johnson 225 Venom

  9. #9
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    Keep us posted, I'm thinking about doing the same on mine. I have looked a few times on EBAY and never found any, How did you search for them?

  10. #10
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    Where are these relief holes you refer to. And what does plugging them do for performance????

  11. #11
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    The idle relief holes are in the cylinder sleeves. Plugging them bumps up the compression, just like using the smaller 2.7 heads.

    I've always heard that bumping up the compression in general gives you a bigger boost in low end power, but doesn't do much for you on the top end.
    Ian

    ...boatless for now.

  12. #12
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    If you are going to run the 2.7 heads make sure the engine will turn at least 5700, prefer to see them at 6 plus. 5500 wot with 2.7 heads is asking for trouble.

  13. #13
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    I will have to go to my ship next week. Will be on the big blue ocean for 10 weeks, so I won't be able to report on any results until I get back home late July or so. Gotta earn some money too...

    prov1x - Try searching: head* (398268, 398268, 331490) and remember to tick the box "Search title and description. Then search: head* (johnson, evinrude, omc) (200, 225) (1986, 86, 1987, 87) That should do the trick.

    Thanks for the rpm recommendation Racer. I will prop the motor to run light. I have some other props to try and I will probably try to trade that 26" Raker II for a 24". My boat is heavy at 1200lbs + 450lbs motor + 160lbs fuel + 200lbs driver + assorted stuff.

    Thanks guys:-)
    Hal
    Hal

    "Ton o' metalflake" 1982 Concord Mach II with 1997 Johnson 225 Venom

  14. #14
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    you should measure the chamber depth from bottom of bowl to deck see what they are i have a set .59 totally almost useless 150 psi unless you want to run higher octane worth checking before you put them on

  15. #15
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    Quote Originally Posted by imq707s View Post
    The idle relief holes are in the cylinder sleeves. Plugging them bumps up the compression, just like using the smaller 2.7 heads.

    I've always heard that bumping up the compression in general gives you a bigger boost in low end power, but doesn't do much for you on the top end.
    Low end and mid range was seriously improved when we tightened my brothers $30 motor up

    We started with a 89 3.0 that came out of a commercial mullet boat with approx 1000hrs and 70psi probably 50% leak down . Since we had literally $30 in the motor we took 2.7 heads and had them cut till compression was around 115 put the used head gasket back on and then re-jet a bit. With a 30 chopper on the action it would barley get out of the hole, after the compression bump it hopped up with a quick blip and made the boat feel like it lost 300lbs I could not believe the difference in hole shot (im sure it had more to do with the compression bump but the 2.7 chambers do help). Then we took it and put 90 miles on it at RR . The heads make a little over 150 on the fresh ported motor so we run good 93 in it no more 87

    Im sure Al is doing a face palm while shaking his head after reading this but we had fun
    Last edited by baja200merk; 05-04-2011 at 09:50 AM.
    Quartershot T-3R 15" 3.5L E-Tec 1.62 Sportmaster


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