The automotive confusion aside, Ppk will always be greater than Cpk since Ppk is long term capabliity and Cpk is short term capability. The only way that Cpk will be greater than Ppk (other than a misuse of the terms and formulas) is under the conditions stated in a previous post.
Can PPK be more than Cpk?
In short, Yes, Ppk can be larger than Cpk. Cpk is an index that is designed to communicate the state of quality of what you are measuring. Cpk uses three pieces of information to calculate the index: The mean or average of the data that was collected.
Which is better Cpk or PPK?
Ppk tends to be more realistic because it doesnt cut out real data, while Cpk data gathering could inadvertently skew the data into looking like a process is capable but not addressing its performance.
Why is CP higher than Cpk?
As you know, the greater the value of Cpk, the better is the capability of the process to produce parts within Specification. While only Process variation influences the Cp value, both Variation and central tendency influences Cpk. This is why Cp will always be greater than or equal to Cpk.
How close should Cpk and PPK be?
According to Six Sigma philosophy, Cp or Pp and Cpk or Ppk should be greater than 1.50.