Excellent Stijloor, I woldn't look for past questions.
kedarg6500, Maybe your question
is there any proportional relationship exsists
was not answered the way you would like.
cpk = cp if the variation is centered to the specs.
there is no proportional relationship (unless centered- that is direct), because cp is held constant while cpk varies depending on the centering of your process,
desto different cpk values, the same cp - no proportionality constant