I think 11-13 % is okay.

A rule of thumb from Puma Racing:
FWD cars - add 10 to the wheel bhp and then divide the result by 0.9


Coupé Fiat 20V Turbo Plus 1999, T19 Mitsubishi turbo
https://youtu.be/O9qrLj3Ap00 Now FCP Stage3!