Power Derating for Emissions & Site Conditions
| Parameter | Formula / Typical Value |
|---|---|
| Altitude Derating (NA) | ~3% per 1,000 ft above sea level |
| Altitude Derating (Turbo) | ~2% per 1,000 ft above sea level |
| Temperature Derating | ~1% per 10°F above 60°F |
| BMEP | (HP × 33,000) / (L × A × N × n) |
| Torque | (HP × 5,252) / RPM |
Understand engine derating methodology for emissions compliance and site conditions
Engine HP re-rating calculates the derated horsepower available from a natural gas engine after accounting for altitude, ambient temperature, humidity, and emissions control modifications.
Naturally aspirated engines typically lose about 3% of rated horsepower per 1,000 feet of elevation above sea level due to reduced air density. Turbocharged engines lose approximately 2% per 1,000 feet.
Emissions derating varies by modification type: prechamber conversions typically reduce HP by 3-5%, lean burn conversions by 5-15%, and timing retard by approximately 2% per degree of retard.