Yes, an OBD2 scanner can measure horsepower, but not directly. It calculates horsepower based on other data points like vehicle speed, acceleration, and weight. Let’s explore how this works and what factors influence the accuracy of these readings.
A chart displaying engine performance data, including torque, horsepower, and boost pressure, captured from an OBD2 scanner and visualized using Google Sheets.
How OBD2 Calculates Horsepower
OBD2 software utilizes a complex formula to estimate horsepower. By monitoring vehicle speed and its rate of change over short intervals, along with the vehicle’s total weight, a reasonably accurate horsepower figure can be derived. This calculation measures horsepower at the wheels, often referred to as “wheel horsepower” (WHP), which differs from the horsepower measured at the engine’s flywheel (BHP).
Key factors in this calculation include:
- Vehicle Speed and Acceleration: Constant monitoring of speed and acceleration provides the foundation for the horsepower calculation. Zero acceleration means zero horsepower at the wheels.
- Vehicle Weight: Accurate vehicle weight is crucial. The heavier the vehicle, the more power required to accelerate it, impacting the calculated horsepower.
- Drag Coefficient: OBD2 software compensates for aerodynamic drag, using an average drag coefficient and frontal area to refine the horsepower estimate.
To ensure accurate weight input, using a certified weigh station is recommended. Alternatively, you can estimate the weight by combining the manufacturer’s specified curb weight with passenger weight, fuel load, and any additional cargo.
Calculating Torque with OBD2
Torque, a rotational force, is calculated using engine power (horsepower) and RPM (revolutions per minute). With these two data points, OBD2 software accurately estimates torque at the wheels, mirroring the horsepower measurement location. Vehicle weight also plays a crucial role in torque calculation, highlighting the importance of accurate weight input.
Measuring Boost Pressure with OBD2
Boost pressure, essential for turbocharged or supercharged engines, is determined using the intake manifold absolute pressure (MAP) and barometric pressure.
- MAP Sensor: This sensor measures the pressure within the intake manifold.
- Barometric Pressure: Atmospheric pressure, influencing engine performance, is either directly measured by the vehicle or a default sea-level value is used.
Negative pressure readings indicate vacuum, while positive values signify boost from a forced induction system. Your vehicle must support MAP data for boost pressure readings to be available.
Enhancements in OBD2 Software
Recent updates to OBD2 software have significantly expanded its capabilities beyond calculating performance parameters. Notably, full support for Mode $06 scaling IDs, including 12 new identifiers introduced in the latest OBD2 standard, has been implemented. This allows for more comprehensive diagnostics and data analysis.
Conclusion
While an OBD2 scanner doesn’t directly measure horsepower, it can provide a reliable estimate based on several factors. Understanding the principles behind these calculations and ensuring accurate vehicle information input will yield the most reliable results. Utilizing the latest OBD2 software with expanded features ensures access to the most comprehensive vehicle data and diagnostics.
