Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
SAE Gross Horsepower
« Back to Glossary Index
SAE gross horsepower is an outdated method of measuring the maximum power output of a production engine, typically measured at the flywheel or crankshaft using a dynamometer. This standard was developed by the Society of Automotive Engineers (SAE) and was widely used prior to 1973.
Key Characteristics:
- Measured with the engine mounted on a test stand, free of many power-draining accessories.
- Includes only components essential to engine operation, such as:
- Fuel pump
- Oil pump
- Ignition system
- Excludes accessories like:
- Alternator
- Water pump
- Cooling fan
- Power steering pump
- Exhaust system
- Air cleaner and emission control devices
This testing setup creates ideal laboratory conditions, allowing the engine to operate without external parasitic loads, thereby yielding inflated horsepower figures compared to real-world use.
Historical Context:
- Used until 1972, after which it was replaced by the SAE net horsepower standard, which measures power with all standard production accessories installed.
- The change to net ratings caused a notable drop in published horsepower figures, even though the engine’s internal performance had not changed.
Comparison:
| Feature | SAE Gross Horsepower | SAE Net Horsepower |
|---|---|---|
| Accessories Attached | Minimal (bare engine) | All production accessories |
| Exhaust System | Excluded | Included |
| Cooling System | Excluded | Included |
| Realism | Overstated power | Realistic vehicle power |
| Era Used | Pre-1973 | 1973 onward |
Related Terms:
- Brake Horsepower (bhp): The measured output at the crankshaft without drivetrain losses.
- Horsepower (hp): A general unit of power; often used interchangeably with bhp in automotive contexts.
Summary:
SAE gross horsepower provides a best-case scenario power rating of an engine, useful for lab comparison but not representative of installed, real-world performance. It has been replaced by SAE net horsepower, which reflects true engine output under normal vehicle operating conditions.
« Back to Glossary Index
