YZ250 compression ratio range

[ace402]

On Yamaha's website they list a range for the compression ratio. Why is that?

http://www.yamaha-motor.com/sport/products/modelspecs/30/0/specs.aspx

[trailhead2004]

To the best of my knowledge, the variable ratio come from the power valve oepration. It moves the exhaust port lolwer edge up and down so that would change the compression ratio. I guess that's assuming it is never lower than the intake/transfer port.

trailhead:ride:

[schmollball]

I think its because of the power valve. Different compression open vs. closed. Correct me if I'm wrong.

[ace402]

Ahh, gotcha!