XR250 compression - what should it be

My Clymer manual states the compression should be 192psi or 13.2 on my 1991 XR250R. 

All the replacement pistons i am looking to buy and posts here on TT refer to compression around 10-11 bar or approx 147psi. 

Is the manual wrong or am i not equating the compression ratio to psi right some how ?

interesting my book says 185 - 213psi for a compression test. and stock compression ratio is 10.2:1 . with compression ratio it refers to the space in the cylinder and combustion chamber. with the piston at BDC  the air space is 10.2 units and with the piston at TDC that 10.2 units of air is compressed into 1 unit = 10.2:1

a compression test is a measurement of the pressure pushed by the compression of air.   I hope that makes sense and clears things up.

thanks all - i think i understand why CR calculated and measured will be different.

shame the manual doesn't give a figure that can measured. i'm thinking around 140 psi is the target on a gauge, i don't reckon i'm gonna see 192 psi on my gauge anytime soon

 

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