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Thread: squish limits?

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    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    squish limits?

    I've read how to measure squish, but where can I find squish limits for a 750 and 780? Thanks guys.


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    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    ?????????????

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    Ping Mr Squishington!

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    Connecticut CrazyA's Avatar
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    It's a loaded question. One could have a fairly tight squish with a huge bowl, or one could have a fairly loose squish and a tiny bowl. Too many variables.

    I will say OFF the record, I know peeps who have run them at .060 on premium pump fuel but wouldn't go any tighter than that. That's on a bone stocker. And again, this is OFF the record. Your results may vary!!!


    .

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    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    I'm not holding anyone to anything, Just wondered why everyone tells me to check my squish, but I can't find limits. I run only 92 or better octane in my ski. I'm putting on an OP head that I think was decked. Making me wonder if this high compression head, will be even higher?

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    Whats the compression on it with the new head?

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    I think you should be in the .065+ range for a stock head, BUT, I'm not positive.

    Just hoping to give you an idea. If you find results tighter than that, I would definitly suspect cut heads.

    But i've seen some race heads with low CC's that have bigger squish (.060) and ive seen some with tight squish (.045) Basically what CrazyA was saying.


    To determine your fuel needs you're better off CC'ing the heads.

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    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by 4stroker View Post
    Whats the compression on it with the new head?
    I haven't tried it yet, if the squish will be too tight, there's no reason to even bolt it up.

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    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    How would I go about ccing the head? Using the squish measuring method in the tech section, I believe I'm close to .060 with this OP head. I need a mic to get an exact measurement, I just visually compared it to the variable sizes of solder I bought to do the test.and came up with the .060. I think they decked the head and reground the squish making the bowl even smaller than from OP.

  10. #10
    PolarisNut's Avatar
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    Quote Originally Posted by xlint89 View Post
    How would I go about ccing the head?
    Get a burette and a 1/4" plexi-glass plate. Drill a small hole in the plate and seal it to the head with grease. Install a spark plug and fill the head through the hole with fluid from the burette (Marvell Mystery Oil works well). Pretty easy, but can get a bit messy. Tough call on the squish clearance on that motor...it totally depends on the motors rpm, squish band width, squish angle, compression ratio, and porting. There is an ideal maximum squish velocity that will work, but you have to crunch some numbers to come up with it. FWIW, I've been running .058" squish on my snowmobile, and that motor turns 8300 rpm. The higher the rpm with a given squish setup, the higher the squish velocity. Too high and you can have problems...too low and the motor won't run very well. The heads that I have had good luck with have a fairly tight squish, fairly shallow squish angle (only a degree or two more than the piston crown), fairly narrow squish band, and moderate compression.

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