The Cummins 855 Big Cam represents a legendary naturally aspirated diesel engine that laid the groundwork for modern high-performance powertrains. Designed for demanding applications, this 12-liter powerhouse balances durability, efficiency, and robust torque delivery.
Originally developed for heavy-duty trucks and buses, the 855 Big Cam combines proven mechanical architecture with advanced timing technology. Understanding its core specifications, performance advantages, and typical use cases helps operators and enthusiasts appreciate its enduring legacy.
| Model | Cummins 855 Big Cam | Cummins NTC 290 | Cummins M11 |
|---|---|---|---|
| Displacement | 11.9 L (726 cu in) | 8.3 L (506 cu in) | 10.9 L (667 cu in) |
| Configuration | Inline-6, naturally aspirated | Inline-6, naturally aspirated | Inline-6, turbocharged |
| Power Output | 195–215 hp @ 2100 rpm | 180–215 hp @ 2100 rpm | 205–260 hp @ 2100 rpm |
| Torque | 485–570 lb-ft @ 1200–1600 rpm | 400–485 lb-ft @ 1200–1600 rpm | 500–620 lb-ft @ 1200–1600 rpm |
| Governed Speed | 2100 rpm | 2100 rpm | 2100 rpm |
| Bore x Stroke | 5.39 in x 6.00 in | 4.88 in x 5.00 in | 5.12 in x 5.31 in |
| Typical Applications | Class 6–8 trucks, motorcoaches, heavy transport | Medium-duty trucks, buses | Heavy-duty trucks, vocational vehicles |
Design and Engineering of the 855 Big Cam
Cummins engineered the 855 Big Cam with a robust inline-six layout and a large single overhead cam to optimize airflow and reliability. The oversquare bore and stroke are tuned for strong mid-range torque, making the unit well suited for vocational hauling and steady highway cruising.
Key attributes include forged steel crankshaft, nodular iron piston assemblies, and hardened valve train components. These choices contribute to a service interval friendly design that withstands high cylinder pressures while minimizing downtime.
Power, Torque, and Performance Characteristics
Power Band and Delivery
Delivering up to 215 horsepower at 2100 rpm, the 855 Big Cam provides a wide and usable power band. The broad torque curve between 1200 and 1600 rpm supports smooth acceleration from low speeds without constant downshifting.
Efficiency and Application Fit
Naturally aspirated operation reduces complexity and parasitic losses, improving fuel economy in steady-state highway work. Operators benefit from predictable performance in regional haul, shuttle, and intercity routes where top-end power is less critical than consistent output.
Maintenance, Reliability, and Serviceability
Routine Service Intervals
Recommended oil change intervals and filter changes align with heavy-duty engine standards. Proper lubricant selection and cooling system maintenance are essential to preserving the long service life of the 855 Big Cam.
Common Wear Items and Inspection Points
Valve springs, injectors, and turbocharger assemblies (if equipped) should be monitored during major overhauls. Detailed service records help identify trends that may prevent unexpected failures in critical operations.
Key Takeaways and Recommendations
- Recognize the 855 Big Cam as a durable, naturally aspirated platform ideal for steady duty cycles.
- Prioritize regular oil and cooling system service to maximize component life.
- Evaluate power needs carefully when considering upgrades or replacements.
- Document all inspections and repairs to support resale value and operational transparency.
FAQ
Reader questions
What types of vehicles commonly used the Cummins 855 Big Cam?
The 855 Big Cam was fitted in Class 6–8 vocational trucks, motorcoaches, and heavy transport tractors, especially where reliable power and low-end torque were prioritized over maximum horsepower.
How does the 855 Big Cam compare to later turbocharged Cummins engines?
Later turbocharged models such as the M11 offer higher power density and improved efficiency under load. The 855 Big Cam remains competitive in applications where simplicity, low-end pull, and robustness outweigh peak output requirements.
Can the 855 Big Cam be upgraded for modern emissions compliance?
Aftermarket solutions are limited due to the engine's design era. Most operators choose to retrofit with updated control systems or transition to newer platforms rather than attempting extensive emission upgrades on the original 855 architecture.
What should I look for when buying a used 855 Big Cam engine?
Inspect the crankshaft for wear, verify injector and head gasket condition, and confirm the integrity of the cooling system. A well-documented service history is a strong indicator of long term reliability.