Doesn't look like its right imo, does it not depend on turbo compressor wheel and blade design as well to determine the a/r together with the housing.

There is another thread somewhere on naisoc/iwsti that measures and compares the exact a/r of each turbo, will have a look for it and share if I can find it again.

Edit: no luck, will keep looking.

__________________
06 STi: 337hp @23psi on E85...
06 STi: 309hp @22psi on 98ron...