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  1. #1

    What should compression be for a 97 785 pro

    Hey guys, what should be the compression for a bone stock 1997 785 pro (without any head work or anything modified)

    Also what is the lower limit where you should perform a rebuild.

    thanks


  2. #2
    My stock 99 ran right around 150 psi.

  3. #3
    Quote Originally Posted by racer114 View Post
    My stock 99 ran right around 150 psi.

    that high eh???? 785 lugs told me 120-125 is stock earlier this summer, and so far he seems to really know his stuff. Racer114, doesn't yours have head work done???

    I did a quick google search and found that 97s have a compression ratio of 6.8:1 but I am not sure what psi that is?????

    thanks

  4. #4
    785 Pro Mick's Avatar
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    For some reason 130 Lbs is what is stuck in my head. Cant really remember as I tested my stock one last year.

  5. #5
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    The manual I have says Compression ratio (full stroke) 11.8:1 for 97. 12.3:1 for 98. I wonder if the 6.8:1 you found is calculated from the point the exhaust port closes? If so, I wonder if that's with the exh valves open or closed?

  6. #6
    I don't know, maybe they upped the compression in later models. I do know that the 99 I had was at least 2 mph faster than the 97 I currently have and that was with aftermarket ponsons and an aftermarket intake grate (on the 99). It also felt quicker, topped out at 7850 rpms and was stock class race legal.

  7. #7
    785 Pro Mick's Avatar
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    Didn't the 99 have the CDI with a higher rev limit? That would make it faster, more RPM = more speed? That is why everyone is after the 99 CDI. I believe the motors were all the same.
    I think that and the hull was the only thing that changed through the years. 97 had the lightest hull.

  8. #8
    Quote Originally Posted by 785 Pro Mick View Post
    Didn't the 99 have the CDI with a higher rev limit? That would make it faster, more RPM = more speed? That is why everyone is after the 99 CDI. I believe the motors were all the same.
    I think that and the hull was the only thing that changed through the years. 97 had the lightest hull.
    the 785 pro (1997)of my brother he test 130 to 133 psi each head , three wiseco brand news std bore and cr. 12.4

  9. #9
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    Keep in mind it may vary from gauge to gauge. Also, I would imagine atmospheric conditions could change the numbers too. My '98 had 125 psi with the stock head and 135 psi with my 91 octane ADA head.

  10. #10
    i just found this article that says 7:1 compression ratio for the 97.

    Also elevation may play a small role, I myself am at 600 feet above sea level.

    Here is the article:

    http://pro785.com/1997.htm

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