Late last year, a mystery insider dubbed Mr. X came forward with alleged information about the yet-to-be-revealed new Cummins engine for the 2025 RAM 2500 and RAM 3500 Heavy Duty pickups. Since then, RAM has finally unveiled the updated pickup, and we can look back and see how much Mr. X got right—and which parts were incorrect.
As predicted, the 2025 RAM 2500 and 3500 Heavy Duty pickups will continue to be powered by 6.7-liter Cummins inline six-cylinder engines. As it has since 2007, the engine will continue to displace 408 cubic inches with a bore and stroke of 4.21 x 4.88 inches. Compression is 16.2:1 and hydraulic valve lifters remain standard.
One technicality that the informant got wrong involves the company’s choice of block material. In 2019, Cummins swapped from a standard gray iron block to compacted graphite iron (CGI). The result was more strength in key places along with lighter weight. It was said that for 2025, Cummins would switch back to gray iron with an aim to improve noise, vibration, and harmonics. However, the new 2025 engine still retains its CGI block material. The cylinder head, however, remains cast iron.
The bulk of the improvements are found around the new cylinder head. Cummins has removed the infamous grid heater and instead returned to glow plugs for cold weather starting. Grid heaters were added in 2003 and have proven highly efficient when it comes to warming intake air in cold weather. However, a fatal design flaw allows a nut to come loose and fall into the intake tract, thereby killing whichever cylinder it enters. Returning to glow plugs removes this potential issue while also removing restrictions in the intake air flow path. Fuel injectors and feed lines have also been moved outside the of valve cover for ease of servicing.
Providing fuel pressure is a new Bosch CP8 high-pressure injection pump. This new injection pump is said to be an improvement over the failure-prone Bosch CP4, although we’re not exactly sure how it’s different. Some suspect the CP8 will feature an improved internal pump and cam lobe profile, and the name change is purely to escape the bad publicity of the CP4 and its variants.
Less is known about the improvements to the engine’s turbocharger. However, it remains a single Holset variable geometry unit. Power output rises to 430 hp at 2,800 rpm and 1,075 lb-ft of torque at 1,800 rpm. The engine is governed at a maximum rpm of 3,200. Gone is the old standard-output engine, with this singular model being fit in all 2025 RAM Heavy Duty pickups. The engine holds 12 quarts of oil with the oil filter now being located in a more easily serviced location at the top of the engine.
Most importantly, Cummins has also announced that it and Stellantis have officially extended their partnership to supply the RAM brand with engines through at least 2030.
