if you are a Cummins You fanatic, you may have memorized the stats for the six-cylinder 6BT offered in heavy-duty Ram trucks. But did you know that Cummins makes even more powerful diesel for military vehicles? The Cummins Advanced Fighting Engine (ACE) produces up to 1000 horsepower. Even more incredible, it takes advantage of opposed piston technology to put two pistons in each cylinder. Therefore, it boasts 14.3 liters of displacement, with just four cylinders.
Cummins makes military engines
Cummins Company is a major military contractor. According to Cumminsits engines power more tracked military vehicles than any other brand.
Cummins Engines already makes a 14.8-liter V8 turbodiesel for the US military called the V903. This engine powers the Bradley Fighting Vehicles and the M109A7 Howitzer. It can generate up to 750 horsepower. Also, Russia’s equivalent of the humvee, the GAZ Tigr, was originally designed around the Cummins 6BT. That being said, Cummins has ceased all engine sales to Russia in the wake of the invasion of Ukraine.
Not surprisingly, when the US military needed a new engine, it awarded its $87 million “Advanced Combat Engine” contract to Cummins. But Cummins has been building its big V903 diesel V8 since 1967, and knew it would have to step up its game to design the ACE. To this end, Cummins partnered with Achates Power (pronounced Ah-kay-tees) to design a truly next-generation engine. The resulting engine takes advantage of efficient opposed-piston technology.
The power of opposing pistons
A stock engine, like the Cummins 6BT in a heavy-duty Ram pickup, only has one piston for each cylinder. This piston moves from the bottom of the cylinder to the top, reducing the volume of the combustion chamber and compressing the air-gas mixture. Once the gas is compressed enough, it ignites and pushes the cylinder down.
An engine with two pistons in the same cylinder, moving towards each other, is much more efficient. One reason is that none of the heat from the combustion cycle is lost in one cylinder head, but instead drives the other piston. Another reason is that you need half the piston travel for a given compression ratio.
Opposed piston engines have disadvantages. For example, Achates Power has had to drive a series of gears so that two separate crankshafts can turn a single PTO shaft. You also need intake and exhaust valves on the sides of the cylinder. Achates uses a supercharger and turbocharger to power certain versions of its opposed-piston engines.
See how one of Achates’ opposed piston engines works in the following video:
Cummins and Achates advanced combat engine generates 1000 horsepower
While Achates produces some opposed-cylinder engines as small as 2.7-liter three-cylinder units, Cummins knew the advanced fighter engine would have to be much larger. For starters, the partners settled on a 14.3-litre four-cylinder engine, although the ACE system is modular and configurable. Future engines will range from four to six cylinders.
The ACE engine family is expected to make between 750 and 1,500 horsepower. Hybridization can further increase these numbers. But increased production isn’t the only benefit of the ACE engine.
As you can see in the image above, the ACE engine is closer to cube perfect than most engines out there, certainly closer than Cummins’ 14.8-liter military V8. This could save critical space on future armored vehicles.
Read about why your diesel truck is future-proof below, or watch Cummins Defense Director Dion Anglin explain the new ACE for yourself in the video below: