Curious about HP loss through the drivetrain.

[KRAM36]

Porsche says my cars has 258 HP from factory. I know this is not at the wheel HP, but how would I account for HP loss on a Tiptronic trans drivetrain? I believe the whp on a manual 2003 Boxster S is 229 HP and figure the Tiptronic would be less then that?

I never did a dyno on it in stock form, so I'm not sure what the car's HP was at the wheels. I've done some upgrades and plan some more and would want to know how much HP I got out of the upgrades.

Thanks!