Engine Mechanical Efficiency (ξm):

\[ \xi_m = \frac{BHP}{IHP} \times 100 \]

Where:

• \(BHP\) is the brake horsepower in horsepower (hp).
• \(IHP\) is the indicated horsepower in horsepower (hp).
• \(\xi_m\) is the engine mechanical efficiency (as a percentage).