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Thread: total cc?

  1. #1
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    total cc?

    trying to get a better idea of my comp ratio... I was thinking I could cc the motor with the head on the block then convert that to a comp ratio? any one know how to do it and have the math equation?

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    Quote Originally Posted by subbietjw View Post
    trying to get a better idea of my comp ratio... I was thinking I could cc the motor with the head on the block then convert that to a comp ratio? any one know how to do it and have the math equation?
    That's the correct way to do it. You need a burette, (with a capacity over thirty CC's) and a way to hold your engine so that your spark plug hole is pointing straight up. You position the piston, at top dead center, on the compression stroke and fill the combustion chamber with fluid.

    If you know the displacement CC's of the engine, you add those to the combustion chamber CC's and divide the total by the combustion chamber CC's. That gives you a compression ratio.

  3. #3
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    I need a what?

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    Do what Al said, otherwise get someone that knows what they are doing, that way you'll have no mistakes.

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    is there something else I could use a little easier to get a hold of at a parts store or something? Im just trying to figure out how much more if any I can mill this head n stay on pump gas? id just go off my comp chart but its too far in the hole for my chart to be close...

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    Quote Originally Posted by subbietjw View Post
    is there something else I could use a little easier to get a hold of at a parts store or something? Im just trying to figure out how much more if any I can mill this head n stay on pump gas? id just go off my comp chart but its too far in the hole for my chart to be close...
    You see, you think it's easy, and it is, if you have the right tools. Without the right tools, it's hard, if not impossible. You can do it with the head off, but you still need a very accurate way to measure the number of CC's that go in the head. Do like Jack said, take your engine to a kart shop that can do it for you. Maybe find your tracks tech man. Pay him to do it.

    There are people that sell precut heads with a certain number of CC's in them. You can calculate the number of CC's in the cylinder with the piston at top dead center. Not exactly, but close enough. I don't suppose you have a spreadsheet that you know how to use? You'll have to take the head off. You'll need some kind of micrometer or depth gauge or calipers. I

  7. #7
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    Go to a farm store and get a 50cc syringe used for animals, it will give you a rough idea.

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    I think we have a place around here I can do that... my comp chart doesn't show predator motors... and im .045 in the hole with no head gasket dish piston and .115 off the head... best I can guess is high 10 low 11 to 1... I want to mill more but I run pump gas... so im guessing im abought the limit with out ccing it... and I do all my own machine work so I have to use what I have...

  9. #9
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    Quote Originally Posted by subbietjw View Post
    I think we have a place around here I can do that... my comp chart doesn't show predator motors... and im .045 in the hole with no head gasket dish piston and .115 off the head... best I can guess is high 10 low 11 to 1... I want to mill more but I run pump gas... so im guessing im abought the limit with out ccing it... and I do all my own machine work so I have to use what I have...
    What octane pump gas? You're getting really close to too high a compression ratio for even the high-octane fuel.

    In my opinion, you don't want to guess!

  10. #10
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    I used this online calculator.

    http://www.csgnetwork.com/compcalc.html

    Enter the values and bam, you have it. Of course, its only as accurate as the numbers you input.

  11. #11
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    Speaking of Burettes, good quality Plastic ones are available that usually don't break like the older glass ones do, I found mine on line, at a reasonable price.

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    that's why I need to cc it... ive been running on pump gas 91octane... haven't heard any pinging or anything bad from her yet... lol

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    Quote Originally Posted by alvin l nunley View Post
    What octane pump gas? You're getting really close to too high a compression ratio for even the high-octane fuel.

    In my opinion, you don't want to guess!
    that's why I need to cc it... ive been running 91 octane haven't heard any pinging or fuss out of her yet... lol

  14. #14
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    Quote Originally Posted by subbietjw View Post
    I think we have a place around here I can do that... my comp chart doesn't show predator motors... and im .045 in the hole with no head gasket dish piston and .115 off the head... best I can guess is high 10 low 11 to 1... I want to mill more but I run pump gas... so im guessing im abought the limit with out ccing it... and I do all my own machine work so I have to use what I have...
    Tim in your case, i would mill the head flat down to the fin, you will have plenty of piston to head clearance with the piston being that deep, more than you will need actually. I doubt you have 11:1 even with the head milled .115. 93 pump has can work just fine even with 13:1 compression. I have an engine that is 11.5:1 and still running 87 without any detonation. If this was a clone block you could just put a predator crank in it and get the piston up in the hole a bit more, but im assuming its a predator since this is predator section lol. Have you decked the block any? That will help you get the piston closer to the deck as well

  15. #15
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    no just did the head and the first fin is m.i.a. on the shop floor... lol I know theres more space in this motor then my s/a but the head is a long way down I had to change to a short plug cause my ap66 was too long to fit... I had like 4 washers on it and it just started to go to tdc... that's closer then my .065 off and .020 long rod motor... I just need to cc it... and see where im at... hoping I come up short of that 11to1 so I can mill more!!! =)

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