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Discussion Starter · #1 ·
I'm lookin for the low compression ratio for a 92 polaris 440 engine. The low ratio is that of the volume when the exhaust port is just closed to the clearance volume. Anybody happen to know it off-hand?? Or maybe where I could find it out?? Thanks.

deep
 

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i don't know the exact number.why, is your sled ready for a rebuild? i know a arctic cat 440 jag special is 119 per side, so i wouldn't think the polaris would be much less. anything over 110 is pretty ood, anything over 100 is acceptible.
 

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not compresion PSI, he wanted ratio.

My guess would be somewhere around 10:1, but I'm not sure.
 

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Measure the volume of the cylinder when piston is just closing the last port, and compare it to the volume of the cylinder when the piston is at TDC.

-Dean
 

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Discussion Starter · #7 ·
It will be the volume of they cylinder just after exhaust port closing + the cylindre head volume divided by the cylinder head volume. I am pretty sure that that would be how you would find it. All that you would need to do to measure that would be to fill the cylinder and head with water and measure the amount. 1mL = 1 cc.

deep
 

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Thanks,

Is that like the compression ratio in a car which determines what octane fuel you should be using. 12:1 would be pretty healthy in a V8 and would need premium fuel. Is that fairly average for a sled?
 

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Discussion Starter · #9 ·
I think that the high compressio ratio (that of the whole displacement/squish volume) is around 12:1. Somebody told me that the lower ratio (that of the displacent obove the exhause port)is on the order of about 7:1 or so.

deep
 
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