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Is the Cummins Advanced Combat Engine a Game-Changer or Just a Revival
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Cummins Military Engine Development History
Cummins has long supplied diesel engines for military applications, including the V903 used in the Bradley Fighting Vehicle and the 6BT variants found in logistics trucks. While most commercial engines have evolved toward emissions compliance and electronic control, military engines prioritize reliability, modularity, and field serviceability. In recent years, Cummins unveiled a new powerplant aimed at next-generation armored vehicles: the Advanced Combat Engine (ACE).
This engine is not just a refinement of existing designs—it’s a radical departure. Drawing inspiration from opposed-piston configurations like the Fairbanks-Morse and Napier Deltic, the ACE uses two pistons per cylinder, eliminating the need for cylinder heads and valve trains. The result is a compact, high-output diesel engine with fewer moving parts and simplified maintenance.
Technical Configuration and Performance
The ACE features:
  • Four cylinders with eight pistons
  • Two crankshafts geared together to a single output shaft
  • No valves—intake and exhaust are controlled by ports
  • Displacement of 14 liters
  • Output exceeding 1,000 horsepower
This design allows for high power density and reduced weight, ideal for armored personnel carriers and mobile artillery platforms. The absence of a traditional valve train means fewer wear points and no valve lash adjustments—an advantage in battlefield conditions.
Terminology Notes
  • Opposed-Piston Engine: A configuration where two pistons share a single cylinder, moving toward each other during compression and away during power stroke.
  • Crankshaft: A rotating shaft that converts reciprocating piston motion into rotational energy.
  • Jake Brake: A compression release engine brake often used in heavy trucks.
Comparisons and Historical Influence
The ACE bears resemblance to the Napier Deltic, a British engine used in naval vessels and locomotives. The Deltic featured three banks of opposed-piston cylinders arranged in a triangle, with three crankshafts. While complex, it delivered exceptional power-to-weight ratios.
The Commer TS3, a British truck engine from the 1950s, also used an opposed-piston layout with a single crankshaft and rockers. It ran at up to 2,000 rpm and was known for its distinctive sound and compact design.
Field Anecdotes and Military Implications
A retired mechanic from Missouri recalled working on M113 personnel carriers powered by Detroit Diesel 6V53 engines. Despite their age, these two-stroke diesels remain in service due to their simplicity and light weight. The ACE aims to replace such legacy engines with a more efficient, modular alternative.
Military logistics favor engines that can be swapped as complete units. Rather than performing in-frame rebuilds in the field, damaged engines are removed and replaced, with repairs handled at centralized depots. The ACE’s compact design supports this philosophy.
EPA and Emissions Considerations
Military engines are exempt from EPA regulations, allowing designs that would be impractical for civilian use. However, the ACE is reportedly EPA-compliant, suggesting potential crossover into commercial or emergency response markets. Its high efficiency and low emissions could make it attractive for specialized applications.
Recommendations for Designers and Technicians
  • Focus on modularity: Design support systems (cooling, intake, exhaust) for quick disconnection and replacement.
  • Train on opposed-piston theory: Understanding port timing and crank synchronization is essential.
  • Monitor gear train wear: Dual crankshafts require precise meshing and lubrication.
  • Use synthetic oil for reduced carbon buildup: Especially important in ported engines without valve scavenging.
Final Thoughts
The Cummins Advanced Combat Engine represents a bold step in diesel technology, merging historical concepts with modern engineering. Its opposed-piston layout, high power density, and modular design make it well-suited for military use—and potentially for commercial applications where space and weight are critical. Whether it becomes a mainstream solution or remains a niche innovation will depend on adoption, reliability, and long-term support.
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