Usually its somewhere between 15-17% quoted - but I never get this percentage thing as if you have 500HP, you're not going to lose more than someone running a stock engine if you have the same running gear Saying that as Captain has an auto it will lose a bit more, so I'd say hes just tipping over 300HP
Going by 17%, that gives my 370z 360+HP (and more likely as I have an auto too)