2025 Ram 6.7L Cummins Specs: A Complete Powertrain Overhaul Guids
Introduction: A New Era of Power and Refinement for Ram Heavy Duty
The 2025 model year marks a watershed moment for the Ram Heavy Duty lineup. For over a decade, the partnership between Ram and Cummins has been defined by incremental gains in power and capability. However, the latest iteration of their legendary diesel powertrain represents a fundamental re-engineering—a comprehensive overhaul that moves far beyond a simple specification increase. This is not just a refresh; it is a strategic reimagining of what a heavy-duty truck’s powertrain should be, focusing on a holistic blend of power, reliability, drivability, and long-term durability.
At the heart of this transformation is the new 6.7L High-Output Cummins Turbo Diesel. In a significant strategic shift, this single, formidable engine is now the exclusive diesel option for the entire Ram 2500 and 3500 pickup range. It is paired with an all-new TorqueFlite HD eight-speed automatic transmission, finally retiring the venerable six-speed automatic and closing a long-standing refinement gap with competitors.
This report provides an exhaustive, data-driven analysis of the 2025 6.7L Cummins powertrain. It delves into the deep architectural changes within the engine, the revolutionary impact of the new transmission, and how these upgrades translate to real-world performance. Furthermore, it examines how this new engineering directly confronts and resolves historical reliability concerns, providing a clear picture of its position in the intensely competitive heavy-duty truck market.
The 2025 6.7L Cummins
More Power, More Gears, More Capability
2025 Powertrain Evolution
For 2025, Ram has streamlined the diesel lineup, making the refined High-Output (H.O.) Cummins the new standard for both 2500 and 3500 models. This chart shows how the new engine compares to the outgoing 2024 options, paired with its new 8-speed transmission.
What’s New Under the Hood?
The 2025 engine isn’t just a software tune. It features significant internal hardware upgrades designed for durability, cleaner operation, and easier maintenance.
New Fuel Pump
A new Bosch CP8 high-pressure pump delivers fuel at up to 32,000 psi for greater efficiency and power.
Glow Plugs
Replaces the iconic grid heater system for cleaner, more efficient cold starts and reduced emissions.
Revised Cylinder Head
Features externally mounted injectors, making future service and maintenance significantly easier.
New Piston Design
A lower 16.0:1 compression ratio optimizes combustion for the new fuel and air management systems.
Easier Serviceability
A new cartridge-style oil filter and revised fuel filter positioning simplify routine maintenance.
Grey Cast Iron Block
The 2025 H.O. engine returns to a proven grey cast iron block for renowned strength and durability.
The 8-Speed Game Changer
The single biggest upgrade is the new 8-speed automatic transmission. It finally unlocks the full potential of the Cummins engine, addressing the one area where Ram trailed competitors.
New 8-Speed Transmission
Better Acceleration
More gears keep the engine in its peak torque band.
Improved Efficiency
Lower RPMs at highway speed for potential fuel savings.
Smoother Shifting
Refined driving experience in all conditions.
Better Towing Control
Lower first gear and more ratios for confident hauling.
A Transformed Driving Experience
Unmatched Hauling Capability
With the new powertrain, the 2025 Ram Heavy Duty lineup continues to post incredible towing numbers. These figures represent the maximum capability for each model with the H.O. Cummins.
The New Benchmark: 2025 6.7L High-Output Cummins Core Specifications
For 2025, Ram has streamlined its diesel offerings for the 2500 and 3500 pickups, consolidating the lineup into a single, potent High-Output (H.O.) configuration. This move eliminates the previous Standard Output (S.O.) version for the pickup line, making the formidable H.O. powertrain available for the first time in the Ram 2500. This strategic consolidation significantly elevates the baseline performance of Ram’s diesel offerings. Previously, the S.O. engine, with approximately 370 horsepower and 850 lb-ft of torque, was the primary diesel option for the 2500.
By making the new H.O. engine the sole option, Ram’s entry-level diesel is now far more competitive against the base offerings from Ford and GM, simplifying the buying process and enhancing the brand’s performance credentials across the entire heavy-duty spectrum.
The core specifications for the 2025 Ram Heavy Duty powertrains are as follows:
- Engine: High-Output 6.7L Cummins Turbo Diesel I6
- Horsepower: 430 hp @ 2,800 rpm
- Torque: 1,075 lb-ft @ 1,800 rpm
- Compression Ratio: 16.2:1
- Fuel System: New High-Pressure Common Rail with Bosch CP8 Pump
- Standard Transmission: TorqueFlite HD 8-Speed Automatic
For buyers considering the standard gasoline powertrain, the venerable 6.4L HEMI® V-8 remains, offering 405 horsepower and 429 lb-ft of torque, also paired with an eight-speed automatic transmission.
| Feature | 6.4L HEMI V-8 | High-Output 6.7L Cummins I6 |
| Horsepower | 405 hp @ 5,600 rpm | 430 hp @ 2,800 rpm |
| Torque | 429 lb-ft @ 4,000 rpm | 1,075 lb-ft @ 1,800 rpm |
| Transmission | 8-Speed Automatic | 8-Speed Automatic |
| Max Towing (2500) | 17,750 lbs | 20,000 lbs |
| Max Payload (2500) | 3,940 lbs | 3,600 lbs |
| Max Towing (3500) | 18,150 lbs | 36,610 lbs |
| Max Payload (3500) | 7,590 lbs | 6,050 lbs |
Under the Hood: A Deep Dive into the 2025 Engine Architecture Overhaul
The 2025 6.7L Cummins is far more than a recalibrated version of its predecessor; it is the result of a ground-up re-engineering of its core components, with each change targeting improvements in power, efficiency, serviceability, and long-term durability.
The Return to Cast Iron: Durability and Design of the New Engine Block
In a notable engineering shift, Cummins has reverted from a Compacted Graphite Iron (CGI) block to a redesigned cast iron block for the 2025 engine. While CGI is known for its high strength-to-weight ratio, the new cast iron architecture has been specifically engineered to enhance long-term durability and better withstand the immense cylinder pressures and thermal stresses of heavy-duty use. This redesigned block also serves as the foundation for the engine’s other major architectural changes, including the new cylinder head and top-feed fuel injectors.
Breathing Easy: The Redesigned Cylinder Head, Valves, and Aluminum Intake
To improve airflow and combustion efficiency, the 2025 engine features a completely new 24-valve cylinder head. This new head boasts improved intake and exhaust port flow and accommodates larger intake and exhaust valves, allowing the engine to breathe more freely. Complementing this is a new, lightweight aluminum intake manifold, which replaces the previous heavy cast-iron unit. This change not only reduces overall engine weight but also further optimizes airflow for better performance and emissions control.
Forced Induction Refined: The New Holset Variable-Geometry Turbocharger
The 2025 Cummins is equipped with a new, high-performance Holset variable-geometry turbocharger (VGT). While Cummins has long relied on its subsidiary Holset for turbocharging, this updated unit features a new compressor housing and more robust, heavy-duty bearings. It is engineered to deliver faster spool-up time, which translates directly to improved throttle response and quicker access to peak torque, a critical advantage when accelerating with heavy loads.
Cold Starts Perfected: The End of the Grid Heater and the Introduction of Glow Plugs
In a landmark change for the 6.7L platform, Cummins has replaced the long-standing intake air grid heater with a modern glow plug system. This is the first time glow plugs have been used on this engine in a Ram truck application. This move was driven by two key factors. First, the advanced glow plug technology delivers faster and more reliable engine starts in cold weather, reducing wait-to-start times. Second, and more critically, it eliminates the risk of the “killer grid heater bolt” failure—a notorious and catastrophic failure point on previous generations, where a bolt could break off the heater element and fall into the engine, causing severe internal damage.
The Fuel System Revolution: Analyzing the New Bosch CP8 Pump and Top-Feed Injectors
Perhaps the most significant upgrade for long-term reliability is the complete overhaul of the high-pressure fuel system. The 2025 engine ditches the often-problematic Bosch CP4.2 high-pressure fuel pump in favor of a new, more robust Bosch CP8 pump. This change is a direct response to the CP4.2’s well-documented tendency for sudden, catastrophic failure, which could send metal shavings throughout the entire fuel system, resulting in repair bills exceeding $10,000. The new CP8 is engineered for greater durability and quieter operation.
This new pump feeds a redesigned fuel rail and a set of new top-feed, dry-service fuel injectors. This injector design not only integrates seamlessly with the new cylinder head but also significantly improves serviceability. The oil and fuel filters have also been relocated to be accessible from the top side of the engine, simplifying routine maintenance.
Shifting Expectations: The All-New TorqueFlite HD 8-Speed Transmission
The single most impactful upgrade to the 2025 Ram Heavy Duty’s driving experience is the introduction of the new TorqueFlite HD eight-speed automatic transmission, which replaces the previous Aisin six-speed automatic. While competitors have offered 10-speed transmissions for several years, this leap from six to eight gears is a massive modernization for Ram, closing a significant gap in powertrain refinement and efficiency.
The new transmission is engineered for enhanced durability, minimal noise and vibration, and seamless shifting through intuitive software control. The tighter gear ratios and intelligent shift mapping contribute directly to a marked improvement in real-world performance. This is most evident in the Ram 2500’s quicker 0 to 60 mph time, which has dropped from 8.0 seconds in the 2024 model to just 6.9 seconds for 2025, demonstrating a clear focus on responsive acceleration.
Beyond straight-line speed, the new transmission fundamentally changes the truck’s towing dynamics and efficiency. The additional gear ratios allow the powerful Cummins engine to operate within its optimal RPM range more frequently, reducing strain and improving responsiveness. Crucially, this new gearbox enables the use of a more fuel-efficient 3.42 rear axle ratio to achieve the truck’s maximum towing capacity. The previous generation required a shorter 4.10 axle ratio for the same task, which resulted in higher engine RPMs at highway speeds.
This change reveals a sophisticated engineering strategy. While the 2025 Ram 3500’s maximum towing capacity of 36,610 pounds is a slight decrease from the 2024 model’s peak of around 37,000 pounds, this is not a step backward. It is a calculated trade-off. Ram has chosen to sacrifice a marginal amount of on-paper towing capacity—a figure that very few owners will ever approach—in exchange for a significant improvement in real-world fuel economy, reduced engine noise, and lower component wear during highway cruising for every single owner. This represents a strategic pivot from simply winning the “spec sheet war” to optimizing the overall ownership experience.
Unrivaled Capability: 2025 Towing, Payload, and Performance Metrics
The sum of these powertrain enhancements is a heavy-duty truck platform with formidable real-world capability. The specifications are tailored to meet the demands of both three-quarter-ton and one-ton truck buyers.
Ram 2500 Capability
- Maximum Diesel Towing Capacity: 20,000 pounds
- Maximum Diesel Payload Capacity: 3,600 pounds
Ram 3500 Capability
- Maximum Gooseneck Towing Capacity: 36,610 pounds
- Maximum Conventional Hitch Towing Capacity: 23,000 pounds
- Maximum Diesel Payload Capacity: 6,050 pounds
These capabilities are supported by a suite of available features designed to make towing and hauling safer and more convenient, including a class-exclusive Auto-Level Rear Air Suspension with a Bed Lowering Mode for easier trailer hookup, an integrated Fifth-Wheel/Gooseneck Prep Package, Trailer Reverse Steering Control, and the largest-in-class available 50-gallon fuel tank on certain configurations.
| Capability Metric | Ram 2500 (H.O. Cummins) | Ram 3500 (H.O. Cummins) |
| Max Conventional Towing | 20,000 lbs | 23,000 lbs |
| Max 5th Wheel/Gooseneck Towing | 20,000 lbs | 36,610 lbs |
| Max Payload | 3,600 lbs | 6,050 lbs |
The Heavy-Duty Showdown: 2025 Cummins vs. Power Stroke and Duramax
The 2025 Ram Heavy Duty enters a fiercely competitive market, facing off against deeply entrenched rivals from Ford and General Motors. A direct comparison of their diesel powertrains reveals three distinct engineering philosophies.
- Ford Super Duty (F-250/F-350): Ford continues to pursue dominance on the spec sheet, offering two versions of its 6.7L Power Stroke V8. The standard version produces 475 horsepower and 1,050 lb-ft of torque, while the High-Output variant leads the class with an astonishing 500 horsepower and 1,200 lb-ft of torque. Both are paired with a 10-speed automatic transmission. Ford’s philosophy is one of ultimate peak power.
- GM (Silverado/Sierra HD): General Motors relies on the legendary pairing of its 6.6L Duramax V8 and the Allison 10-speed automatic transmission. This combination is rated at 470 horsepower and 975 lb-ft of torque. While not the class leader in raw numbers, the Duramax/Allison powertrain is a benchmark for proven performance and reliability. GM’s philosophy is one of trusted consistency.
- Ram Heavy Duty: With its 2025 updates, Ram’s philosophy has clearly shifted to one of integrated refinement and powertrain synergy. While its 430 horsepower and 1,075 lb-ft of torque figures are no longer the absolute highest, the comprehensive re-engineering of the Cummins engine and its seamless integration with the new eight-speed transmission are designed to deliver superior drivability, real-world responsiveness, and enhanced efficiency.
The choice for a 2025 heavy-duty truck buyer is no longer a simple matter of which truck has the biggest numbers. It is now a choice between distinct engineering approaches: Ford’s pursuit of peak power, GM’s legacy of proven consistency, or Ram’s new focus on holistic, refined performance.
| Specification | Ram 2500/3500 | Ford F-250/F-350 | GM 2500HD/3500HD |
| Engine | 6.7L Cummins I6 | 6.7L Power Stroke V8 | 6.6L Duramax V8 |
| Configuration | Inline-6 | V-8 | V-8 |
| Max Horsepower | 430 hp | 500 hp (High-Output) | 470 hp |
| Max Torque | 1,075 lb-ft | 1,200 lb-ft (High-Output) | 975 lb-ft |
| Transmission | 8-Speed Automatic | 10-Speed Automatic | 10-Speed Automatic |
| Max 2500 Towing | 20,000 lbs | 23,000 lbs | 22,430 lbs |
| Max 3500 Towing | 36,610 lbs | 40,000 lbs (F-450) | 36,000 lbs |
Engineering for Endurance: How the 2025 Upgrades Address Historical Reliability Concerns
One of the most compelling aspects of the 2025 Cummins overhaul is how the engineering changes directly target and resolve some of the most well-documented and costly reliability issues that have affected the 6.7L platform over the years.
- Solving the CP4 Fuel Pump Crisis: The replacement of the Bosch CP4.2 pump with the new CP8 is arguably the most critical reliability upgrade. The CP4.2 was prone to sudden, catastrophic internal failure, often with little warning. This failure would contaminate the entire fuel system with metal debris, requiring the replacement of the pump, injectors, fuel lines, and fuel tank—a repair that frequently cost owners over $10,000. The adoption of the more robust CP8 pump is an engineered solution to this widespread and expensive problem.
- Eliminating the “Killer Grid Heater Bolt”: The switch from an intake grid heater to glow plugs completely removes a known, engine-destroying failure point. On previous models, a bolt securing the grid heater element could fatigue, break off, and fall directly into the intake manifold, where it would be ingested by a cylinder. This would cause catastrophic damage to the piston, cylinder head, and valves, often requiring a complete engine replacement. The 2025 design eliminates this risk.
- Tackling Emissions System Woes: The most common complaints about modern diesel engines revolve around the emissions systems, specifically the Exhaust Gas Recirculation (EGR) valve and Diesel Particulate Filter (DPF). These systems are susceptible to clogging from soot buildup. The 2025 engine’s improved combustion efficiency—a result of the redesigned head, new turbo, and advanced fuel system—is engineered to produce less soot. This reduction in particulate matter lessens the burden on the EGR and DPF, which should lead to fewer regeneration cycles and a lower likelihood of clogging and failure.
- Improving Turbocharger Longevity: The VGT on the 6.7L Cummins can be susceptible to failure from soot buildup, causing the internal vanes to stick, or from bearing wear.11 The new Holset VGT with its redesigned housing and heavy-duty bearings is built to better withstand these conditions, improving long-term durability.
Ownership and Upkeep: A Guide to Maintaining the 2025 6.7L Cummins
Proper maintenance is critical to ensuring the longevity and performance of any heavy-duty diesel powertrain. The 2025 6.7L Cummins follows a structured service schedule that owners should adhere to for optimal reliability.
| Service Item | Interval (Ideal Conditions) | Interval (Severe Duty) |
| Engine Oil & Filter Change | 15,000 miles / 12 months | 7,500 miles |
| Fuel Filters (Chassis & Engine) | 15,000 miles | 15,000 miles |
| Engine Air Filter | Inspect every 15,000 miles, replace as needed | Inspect more frequently, replace as needed |
| Transmission Fluid & Filter | N/A | 60,000 miles |
| Transfer Case Fluid (4×4) | 60,000 miles | 30,000 – 60,000 miles |
| Front & Rear Axle Fluid | 60,000 miles | 30,000 – 60,000 miles |
| Crankcase Ventilation (CCV) Filter | 60,000 miles | 60,000 miles |
| Coolant Flush | 150,000 miles / 10 years | 100,000 miles |
| Valve Lash Adjustment | 150,000 miles | 150,000 miles |
Frequently Asked Questions (FAQ) about the 2025 6.7L Cummins
Is there a Standard Output (S.O.) version of the Cummins for 2025?
No. For the 2025 Ram 2500 and 3500 pickup truck line, Ram has consolidated its diesel offering to a single High-Output version rated at 430 horsepower and 1,075 lb-ft of torque. This engine is now available in all heavy-duty variants, including the Ram 2500. Ram Chassis Cab models will continue to offer a differently rated version of the 6.7L engine tailored for commercial applications.
What is the fuel economy of the 2025 Ram 2500?
Heavy-duty trucks (Class 2b and above) are not required by the EPA to have official fuel economy ratings. Therefore, no official MPG figures are published. However, Ram states that the new powertrain, featuring the TorqueFlite HD eight-speed transmission and a more efficient 3.42 rear axle ratio, is designed to be “more fuel-efficient” and results in lower engine RPMs at highway speeds, suggesting a tangible improvement over the previous model year.
Is the 2025 Ram 2500 available with a manual transmission?
No. The 2025 Ram Heavy Duty lineup is not available with a manual transmission. The new TorqueFlite HD eight-speed automatic is the standard and only transmission paired with the 6.7L Cummins engine.
How do the new engine upgrades affect aftermarket performance tuning?
The fundamental changes to the 2025 engine’s architecture will require new solutions from the aftermarket performance industry. The new Bosch CP8 fuel pump, top-feed injectors, glow plug system, and updated engine control module (ECM) mean that tuning software and performance parts designed for previous 6.7L Cummins generations will not be directly compatible. Owners seeking to modify their trucks will need to wait for aftermarket companies to develop products specifically for this new platform.
Conclusion: The Verdict on Ram’s New Heavy-Duty Heart
The 2025 6.7L Cummins and its integrated TorqueFlite HD transmission represent a paradigm shift for the Ram Heavy Duty platform. This is not merely an engine with more power; it is a meticulously engineered powertrain system designed to deliver a superior ownership experience. The updates signal a strategic pivot away from chasing the highest on-paper specifications and toward a more holistic definition of performance—one that masterfully balances immense power with newfound refinement, real-world responsiveness, and an unwavering focus on long-term reliability.
By directly confronting and resolving the engine’s most significant historical weaknesses with robust, engineered solutions, Ram and Cummins have demonstrated a profound commitment to their customer base. The replacement of the CP4.2 fuel pump and the elimination of the grid heater are not just upgrades; they are resolutions that will build owner confidence for years to come.
In a market segment often defined by brute force, the 2025 Ram Heavy Duty makes its case with intelligence and synergy. It is a truck that is not only stronger but also smarter, smoother, and built to endure. This comprehensive overhaul has resulted in the most compelling and well-rounded heavy-duty powertrain Ram has ever produced, solidifying its position as a leader in the segment, not just on the spec sheet, but on the road where it truly matters.
