The answer is closer to 15%
in reality, but I would accept a dyno reading with a drivetrain loss of up to 18%. Now that's on the high end of scale, and percentages higher than this are highly suspect in my book.
Measuring your engines horsepower and torque (on any given dyno) is crap shoot.
All the dynamometer brands I listed earlier, each have their own unique interpretation of what constitutes the proper drivetrain loss calculations for a particular car.
This why cross referencing one dyno chart to another can be so frustrating.