Decode: Compression Ratio ? - Sportbike Forum: Sportbike Motorcycle Forums
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post #1 of 3 (permalink) Old 12-31-2007, 06:16 PM Thread Starter
Join Date: May 2007
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Decode: Compression Ratio ?

I have a subscription to Sport Ridar Magizine. Reading through the articles I noticed to myself, I dont know what 12:3:1 is.

What does the X ,Y, & Z stand for? In a ratio of 12:3:1 (X:Y:Z)?

Does . . . this stand for . . .
X = atmospheres (atm) of pressure

Y = vaccume pressure

&Z = to 1atm

If So . . . am I right to think . . .
The compression ratio of the 08' CBR1000RR, is 12:3:1. So it has a compression of 12atm, and a vaccume pressure of 3atm.
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post #2 of 3 (permalink) Old 01-01-2008, 09:15 AM
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Umm, I think you (or the magazine) meant 12.3:1 ("12.3 to 1") which is a compression ratio.

Compression ratio is strictly the ratio of the volume in the cylinder and combustion chamber when the piston is down, vs. when it is up. It has absolutely nothing to do with atmospheric pressure or anything like that.

Note that this ratio includes the volume in the combustion chamber that is not displaced by the piston, so you can increase the compression ratio by reducing this space (i.e. thinner head gasket) without changing the engine displacement (total volume displaced by the cylinders.)
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post #3 of 3 (permalink) Old 01-01-2008, 10:33 AM Thread Starter
Join Date: May 2007
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Well, your right . . . i guess im a wee bit dyslexic
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