Cummins
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Developments in combustion efficiency and turbocharging are enabling modern diesel engines to deliver performance once reserved for larger displacements
For decades, engine displacement has been treated as a proxy for machine capability. If an application demanded more power, more torque or greater productivity, the answer was often to spec a larger engine.
Advances in engine design are challenging that convention. Improvements in combustion efficiency, turbocharging, fuel systems and electronic controls mean modern diesel engines deliver performance levels once only achievable with significantly larger displacements. As a result, OEMs are increasingly asking what smaller engines are capable of delivering.
Smaller engines, big advantages
The latest generation of Cummins engines demonstrates how power density has evolved across multiple displacement classes.
At the compact end of Cummins’ global engine portfolio, the 2.8-litre QSF2.8, available for the North American market, delivers up to 55kW (74hp) and 300Nm of torque, offering performance comparable with many traditional 3.6-litre engines. This allows OEMs to specify more compact engines, without sacrificing the output needed for demanding compact equipment applications.
The same trend continues through the Cummins Performance Series. The 3.8-litre F3.8 Stage V engine produces up to 129kW (173hp) and 600Nm of torque, while the 4.5-litre B4.5 Stage V engine delivers up to 149kW (200hp) and 780Nm. These outputs allow engines with fewer cylinders and lower displacement to perform duties that would previously have required considerably larger powerplants.
Further up the range, the B6.7 Stage V engine produces up to 243kW (326hp) and 1,375Nm of torque. Compared with its predecessor, the engine delivers 5% more power and 31% more peak torque than previous-generation equivalents, demonstrating that increasing performance no longer depends on increasing displacement.
Across the full range from Cummins, higher power density is allowing OEMs to achieve the capability they require from increasingly compact engine platforms.
New opportunities
Higher power density is valuable, but some of the biggest benefits come from what smaller engines enable elsewhere. A more compact, higher power density engine gives OEMs greater flexibility to optimise machine architecture. Engineers can improve visibility from the cab, increase hydraulic capacity, enlarge fuel tanks or redesign cooling packages, without increasing overall machine size. Reducing engine weight can also improve weight distribution and maneuverability, while maintaining productivity.
Cummins’ lighter engines can also contribute to lower operating costs throughout the machine’s lifetime, since they deliver improved fuel efficiency and reduced emissions. Rather than simply a packaging decision, engine downsizing becomes a means of improving the efficiency and economics of the entire machine.
Beyond displacement
Modern compact engine design is helping simplify installations and reduce system complexity.
Cummins’ EGR-free Performance Series architecture, combined with its compact Single Module aftertreatment, enables Stage V compliance with reduced packaging demands. This aftertreatment system is approximately 40% smaller and 20% lighter than the previous generation, giving OEMs additional installation flexibility while maintaining emissions levels.
When combined with factory-integrated options that arrive largely pre-approved for installation, manufacturers can also reduce engineering time, simplify machine development and accelerate time to market.
Redefining capability
Displacement will always remain an important engineering specification, but it is becoming a less meaningful measure of overall machine capability. Higher power density enables engineers to optimise the entire machine rather than simply specifying a larger engine to achieve their performance targets.
As equipment continues to evolve, the most capable machines will be those that make the smartest use of displacement. These advances in engine technology mean that capability is no longer defined by size alone. Instead, it is measured by how effectively an engine maximises productivity, improves efficiency and delivers value across the lifetime of the machine.
