When delving into the performance of vehicles like the BMW M240i, horsepower is a key metric that grabs attention. But where does this horsepower figure actually come from? It’s crucial to understand that official horsepower numbers, especially for cars like the M240i, are meticulously measured at the engine’s output shaft, using an engine dynamometer (dyno). This standardized process ensures accuracy and consistency across different manufacturers.
To truly appreciate the M240i Horsepower or any car’s power rating, it’s helpful to know the evolution of these measurement standards. Historically, “Brake Horsepower” (BHP) was a common term, particularly in the muscle car era. BHP, under the SAE gross power standard, represented the engine’s output without many of the accessories that consume power in a real-world vehicle. Imagine an engine tested in a lab, stripped of its alternator, radiator fan, and even the standard exhaust manifolds – that was BHP.
Alt text: Engine dynamometer in operation, measuring horsepower at the crankshaft, illustrating the standard testing method for car manufacturers.
However, the automotive industry moved towards more realistic measurements. In the early 1970s, SAE standard J1349 replaced BHP, introducing “net power.” This new standard accounted for power-consuming accessories like the water pump, emissions control systems, exhaust, and air cleaner. This net power figure gave a more accurate representation of the power available once the engine was installed in a car.
The pursuit of precision didn’t stop there. In 2005, “SAE Certified Power” was introduced, further tightening the standards. For automakers seeking SAE certification, testing now had to be conducted in accredited labs, witnessed by an accredited third party. This rigorous process aimed to eliminate any ambiguity and ensure that claimed horsepower figures were verifiable and trustworthy.
Germany also has its own standard, DIN (Deutsches Institut für Normung), which is very similar to the SAE net power standard. Like SAE net power, DIN measurements are taken at the crankshaft with all ancillaries connected, and power is expressed in PS (Pferdestärke, which is metric horsepower). Across Europe and globally, various standards exist, but they share a common principle: official car manufacturer horsepower figures are determined at the engine crankshaft. Crucially, these figures are not derived from measurements taken at the wheels.
This distinction is critical because measuring horsepower at the wheels, using a chassis dynamometer, introduces a range of variables, especially for turbocharged cars like the BMW M240i. Chassis dynos measure the power that actually reaches the wheels after passing through the drivetrain, which includes losses from the transmission, driveshaft, differential, and tires. Furthermore, using “correction” factors on chassis dynos to compensate for temperature, elevation, and other environmental conditions can often lead to inflated and unreliable horsepower figures, particularly for turbocharged engines.
Alt text: Close-up view of a BMW M240i engine bay, highlighting the powerful turbocharged engine responsible for its impressive horsepower.
While chassis dynos are valuable tools for tuning and comparing before-and-after modifications on a specific vehicle, they are not ideal for determining the absolute, manufacturer-stated horsepower of a car like the M240i. For reliable M240i horsepower figures, it’s best to trust the official numbers published by BMW, derived from standardized engine dyno testing. These figures represent the true output of the engine itself, measured under controlled conditions. When it comes to understanding the real power of your M240i, or any performance vehicle, focusing on manufacturer-provided crankshaft horsepower is the most accurate approach.
