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  1. #11
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: A word about cheap compression testers

    Quote Originally Posted by thudd3rski View Post
    looks like the issue with the hf tester is the hose that comes with it...it has no valves in it, so the volume of the
    hose and fittings is added to the relatively small space actually being tested.
    That seems to be a common complaint that compounds the errors.


    Calculating the actual compression is easy, and even for beginner.
    It is a good project to calculate the geometric compression ratio
    with a piece of plexi-glass a graduated syringe, a digital caliper,
    and general info from google.

    Atmospheric pressure in psi x geometric compression ratio = cranking psi.

    I often recommend 15 psi (14.7), but using data from Air Density Online
    you can estimate the compression based on the local weather conditions
    recorded daily at a nearby race track (Very important if you live in a state
    with large temperature swings in a year. exp: Arizona, California, or at an
    elevation).

    1). Select a nearby race track.
    2). Write down the Uncorrected Barometer (as an example: At Alabama
    International Dragway the current Uncorrected Barometer is 29.59 inHg)
    3). Use Google to convert 29.59 inHg into psi = 14.533251psi.
    4). Calculate cranking psi: 14.533251psi x 10:1 compression ratio = 145.33psi

    My original source for calculating compression using the geometric CR was PSI
    Racing, but it just uses the Gas Laws to calculate the psi.

    I am aware of trapped CR vs geometric CR. I was originally skeptical of using the
    geometric CR instead of the trapped CR, but the geometric CR is so easy and it
    is accurate.


    Bill M.
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    Last edited by wmazz; 11-30-2021 at 01:22 PM.
    Horsepower == Speed, RPM != Speed



  2. #12
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: A word about cheap compression testers

    Quote Originally Posted by JC-SuperJet View Post
    Uhmmm...don't know where on the Internet I read this, but

    CHANGE OUT THE SCHRADER!!
    BWAAAhhhhaaaahhaaa!!!!
    http://www.facebook.com/twinlakesjetskirepair

    '89 Kawi 650SX 42.4 GPS
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  3. #13
    PWCToday.com Is My Home Away From Home
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    Re: A word about cheap compression testers

    Quote Originally Posted by thudd3rski View Post
    I tried an hf gauge and it read way low...can you recommend a decent compression tester for use once in a while?
    Quote Originally Posted by thudd3rski View Post
    i verified the hf readings back to back with a snap on compression tester...harbor freight tester 60 psi...snap on was 150 psi.

    now hf sells more than one tester...maybe the "nicer" one has better accessories and the error can be resolved by replacing the valve...just guessing here
    I don't see the need to get another gauge or fix the HF one if you have access to a Snap-On.
    Riding mostly Lake Austin

    1984 JS440 -- 1989 650sx -- 1991 X2 -- 1992 750sx -- 1995 900zxi (qty 2) -- 1995 X2

    Quote Originally Posted by cujo View Post
    God intended PWC to be two strokes, as well as dirt bikes, snowmobiles, and chain saws....

  4. #14
    PWCToday Newbie thudd3rski's Avatar
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    Re: A word about cheap compression testers

    Quote Originally Posted by linkman View Post
    I don't see the need to get another gauge or fix the HF one if you have access to a Snap-On.
    had access

    and thanks wmazz for the helpful answer

    and for those not actually reading the linked material, changing out the schrader isnt going to fix a flawed design. makes more sense to just buy a properly designed tester
    Last edited by thudd3rski; 11-30-2021 at 09:05 PM.

  5. #15
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: A word about cheap compression testers

    When I was a mechanic, I used the geometric compression ratio to
    determine what the cranking compression as a guideline for my
    tune & service compression tests, when the geometric CR was
    in the service manual.


    Bill M.
    Last edited by wmazz; 12-01-2021 at 01:34 AM.
    Horsepower == Speed, RPM != Speed



  6. #16
    PWCToday.com Is My Home Away From Home Bionic racing's Avatar
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    Re: A word about cheap compression testers

    Good link on Schrader valves , even snap ons need new valves from time to time , and the snap on tool guy is hard to find @ times , adavanced auto is in town , price is good , thanks myself

  7. #17
    PWCToday.com Is My Home Away From Home WFO Speedracer's Avatar
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    Re: A word about cheap compression testers

    HF compression tester is crap on a stick, what good is a compression tester that won't measure compression ?
    Y'all know me, still the same O.G. but I been low-key
    hated on by most these &^$$@s with no cheese, no deals and no G's, no wheels and no keys, no boats, no snowmobiles, and no skis, mad at me cause I can finally afford to provide my family with groceries

    WWSRD , What would Speed Racer do ?

  8. #18
    Top Dog orangefinger's Avatar
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    Re: A word about cheap compression testers

    and as always.....if you high , its low ( now that's funny ) ........greetings from high altitude riders :0)
    KELLYHIEKE.ROCKS NEW WEBSITE CHECK IT OUT - FEMALE AMATEUR FREESTYLE

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  9. #19
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    Re: A word about cheap compression testers

    Quote Originally Posted by WFO Speedracer View Post
    HF compression tester is crap on a stick, what good is a compression tester that won't measure compression ?
    The HF tester may very well be junk. The most important part of a dynamic compression tester is that the valve is mounted at the bottom of the spark plug threads. If the valve is mounted further away or if its slow to close and seal, the reading will be low. The pressure qauge itself can be checked against any other for accuracy. I still use a 35 year old El-cheap-O tester. I just change the valve and check the guage from time to time.
    Last edited by kweasel; 12-02-2021 at 05:57 PM.
    What exactly does the IJSBA do?

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