Attention: TDR Forum Junkies 
TDRComm
Staff Member
FIRST REVIEW: 2025 CUMMINS ENGINE
It was only two weeks ago that the folks at Ram gave members of the press the first ride-and-drive opportunity at their product launch in Laughlin, Nevada. (Think Davis Dam area and the test route for published SAE towing ratings.)
Above: Testing the 2025 Ram HD truck at Davis Dam
TDR writer Bruce Smith was a part of the press group that attended the mid-March product introduction. And, while G.R. Whale gave us a “First Drive” report, Bruce’s report gives us a “First Review” of the 2025 Cummins Engine. Yes, Bruce’s focus was a series of questions that were specific to the Cummins folks at the product launch. The following is his report.
Read the entire discussion below or click HERE to download the file to save, print and/or read later.
THE 2025 CUMMINS 6.7L ENGINE - by Bruce W. Smith
Images courtesy of the author, Ram Truck/Cummins, and Geno’s Garage staff.
It’s been 36 years since the marriage between Cummins and Ram (Dodge) was consummated with the 5.9-liter, 12-valve, 6BT Turbo Diesel being offered in the ¾- and one-ton pickups. Since that time the partnership has evolved as technology and buyer demands have pushed the growth in size, performance and reliability of both trucks and engines to historically new levels. This is exemplified in the 2025 Ram Turbo Diesel 2500, 3500 and Chassis Cab models sporting the High-Output 6.7-liter Cummins, 24-valve engine.
While the original 359 cubic-inch Turbo-Diesel in the 1989 truck delivered 160hp and 400 torque, the new engine sets an industry benchmark making 430hp and class-leading 1,075 torque.
I was able to piece together a little “inside look” at what makes the newest iteration of the 6.7-liter Cummins tick during our short time driving several different models of the new trucks during a Laughlin, Nevada media event.
During that time I interviewed numerous engineers on both the Ram and Cummins teams, about the changes that make this new engine “stronger and more reliable than ever before.” Potential buyers of the heavy-duty 2025 Ram pickups should find the candid answers very informative…
All 2025 Turbo Diesel pickups get 430hp and 1075 torque,
commercial trucks are rated at 360/800.
TDR: What generation would this 2025 version of the Cummins 6.7-liter be called—a Generation 5?
Ram/Cummins: Let’s say Generation 4.5. It’s an evolution of the previous engine into a new type architecture. That’s because there are some significant changes. Yes, it is an inline six. But, it’s a new cast-iron block with a new cylinder head. It has a new air intake manifold. It has new serviceable features with flash-over-the-air capability for calibrations. It has a top-feed loop, fuel filter and dual filtration modules. So there’s a lot that’s changed on this engine.
Editor’s note: I’m going with this nomenclature. Fourth Generation 4.0 = 2010-2012. Then Fourth Generation 4.25 = 2013-2018. Followed by Fourth Generation 4.5, 2019-2024 CGI engine. Now, Fourth Generation 4.75, the new 2025 engine.
TDR: It’s apparent an enormous amount of engineering time and money went into designing this newest generation Cummins. What was the primary goal?
Ram/Cummins: So from our standpoint, the primary goal was to create a more efficient product with lower emissions. A more efficient product from not only the power side, but also in fuel economy gains. When you look at the 3500 truck that is paired with the 8-speed ZF transmission, we’re seeing up to 7% better fuel economy than the 2024s. From the emissions standpoint, this is an architecture that can carry us through on the [EPA] pickup platform [regulations] for quite some time.
TDR: Can you expound on the emissions challenge?
Ram/Cummins: Who knows what’s going to happen with the regulations, but we’re preparing for what we know. This architecture, from an investment standpoint for both Ram and Cummins, made sense for us to move forward with and put into production.
TDR: How did meeting potential future emissions goals lead to some of these new features?
Ram/Cummins: That’s a little complicated to explain. There were simultaneous changes made. There were packaging changes that were made because of emissions. For example, we went with the on-engine, diesel oxidation catalyst (DOC). That required the turbo to shift forward a few inches and it altered the Holset turbine housing. And then we had the new fuel pump (Bosch CP8) and top-feed dry injectors.
Above: Passenger side of the 6.7-liter Cummins. The DOC is now very
close to the turbocharger’s exhaust flange. Also circled, the easy-to-service
oil filter has a removable cap (28mm hex head) and a drop-in filter.
TDR: Did any of these changes make it easier to service this engine compared to the previous model?
Ram/Cummins: Serviceability is definitely improved! Again, the changes in injectors and external fuel lines allowed us to use a top-feed,dual module fuel filter in a drop-in canister with easy access from the top driver’s side of the engine. No more crawling underneath the truck to change the primary fuel filter. Both fuel filters are together for easy access. And, the oil filter: No longer do you have to go through the bottom of the passenger-side wheel well for access to the oil filter. Who wants to create all that mess and pain? The oil filter is also a drop-in element, and owners will really appreciate the ease-of-service these filters provide. Again, our goal with this new design was to deliver a product with more efficiency and better serviceability.
Above: Driver side of the new 6.7-liter Cummins. The fuel filters
are next to each other in the engine compartment. You’ll use the same
28mm hex head socket to remove the fuel filter caps as well as the oil filter cap.
Cylinder Block
TDR: When Cummins introduced the CGI (compacted graphite iron) block in 2019, it was touted as being “stronger, lighter and lower NVH than cast iron.” So why the change? Was returning to a gray cast-iron block a cost savings decision on Ram’s part?
Ram/Cummins: No, I would say that we have over 100 years of experience in gray iron. And when I say “we,” Cummins, across all our platforms, has 100 years of experience in gray iron. We have 30-plus years on the Ram platform. From a cooling standpoint we knew we were going to have to make changes to the [CGI] block. Remember, we’re going to higher horsepower and torque. From a manufacturing and technical kind of expertise we could leverage this for the long-term with the grey iron block easier. It is the right decision for us and this product.
TDR: The 2025 engine has a new block. What’s different from the previous versions?
Ram/Cummins: The biggest change in the new block is mainly in the redesign of the water jackets. Water jackets have been optimized for better flow than the CGI block it replaced. Externally, we kept a lot of the key touch points constant, or close to constant, to minimize the integration impact to Stellantis in the truck’s chassis. But, inside it’s really around the cooling system. We revamped the cooling system to more evenly distribute the coolant flow around the cylinders so we get more uniform cooling front to back than we did with the previous generation(s).
TDR: Can you explain a little how the manufacturing and technical aspects played a role in returning to a gray iron block?
Ram/Cummins: In our case, doing the redesign of the cylinder block we’d used since 2019 meant using all our analytical and design tools. Nothing’s static in time. Since we had to make the design changes to the block for emissions and cooling improvements, we took the opportunity to apply the latest analysis and design tools to do it. We saw the path to get back to gray iron and keep the overall package in a similar overall weight standpoint while reaping all the benefits that gray iron has from the ease-of-manufacturing standpoint.
TDR: Is gray iron easier to work with than CGI?
Ram/Cummins: When it comes to the manufacturing and the machining of cast iron versus CGI, in an overall quality play, CGI is a pretty tough material to machine and to deal with. And as far as residual burrs, machining debris, and keeping things of that nature out, gray cast iron lends itself to an overall higher quality and fewer debris-related issues that we’ve experienced at our machining facility.
Engine Internals
TDR: Were there changes in the pistons, crankshaft, rods and bearings?
Ram/Cummins: Sure, but those changes are subtle on the rotating assembly. The pistons were redesigned to optimize the new fuel injectors.
TDR: How has the cylinder head been changed?
Ram/Cummins: The same thought carried through with the cylinder head, better cooling. The compression ratio is the same as before (16.2:1), but we took the opportunity to change the valve spacing because we had that luxury this time to be able to do that, which allowed us to install bigger intake valves and bigger exhaust valves. The intake and the cylinder head as a whole is a complete and total redesign.
TDR: The intake manifold is totally different from the earlier engines, correct?
Ram/Cummins: Yes. We divorced the intake manifold from the previous generation. That change worked hand-in-hand with the new fuel system that I’m sure we’ll touch on here in a bit. Plus, moving from the side-feed injectors of the previous generation to the top-feed we use now, gave us the opportunity to put more optimized and larger intake and exhaust ports in the cylinder head (previously mentioned) to help overall volumetric efficiency. And then there’s a new mass airflow sensor housing and mass airflow sensor on that intake, which relates back to the efficiency play.
TDR: Did these changes play a big part in better fuel economy and that 10hp boost in horsepower?
Ram/Cummins: Yes. When overall volumetric efficiency improved, so did those numbers for speed on grade, and now the 430hp and 1075ft-lbs are available across both the 2500 and 3500. All pickup customers now have access to this rating.
Fuel Injection Pump
TDR: Now to the question that most diesel owners want to know: What is a Bosch “CP8” fuel injection pump that’s used on the new engine?
Ram/Cummins: We needed much higher fuel pressures for this new fuel system. We moved from 32,000 PSI (2,000 Bar) to 39,000 PSI (2,200 Bar). So, some significant improvements and increases were needed in the fuel injection pump. That’s what made us consider a new fuel pump design.
TDR: The CP8 looks identical to the CP4.2. But it’s different inside?
Ram/Cummins: Correct. While the CP8 may look the same, the internals are different with improved pumping and roller elements along with isolated-loop fuel lubrication. In partnership with Bosch and with Stellantis, this pump has gone through significant testing and vast improvements. We’ve developed new tests that not only helped revalidate the older CP3 that has been used since 2003, but also helped validate the new CP8. The tests are run with out-of-specification conditions to ensure we are validating beyond what coud be seen in application.
Above: The “isolated loop” fuel lubrication lines (blue “tick-marks”)
are easily identified in the picture of the CP8.
TDR: I understand one of the validation tests of the CP8 was called the “Killer Test” where the pump was fed worst-case fuel (with contaminants) under the worst conditions, testing the pump until it failed. Can you elaborate?
Ram/Cummins: The test is run with out-of-specification fuels, out-of-specification fuel temperatures, as well as pump speeds and pressures that are not possible in application. The equivalent of operating for thousands of miles under the most severe temperatures with the poorest of fuel. It was created to ensure that the fuel pump in a Ram would have the robustness and durability that Cummins is known for.
TDR: What re-engineering resulted from this broader, much more intensive validation testing of the CP8?
Ram/Cummins: The Bosch CP8 is a new fuel pump. The roller and shoe design that was in the old pump has been redesigned to a pinned roller-tappet architecture. Another major difference is the lubrication circuit of the CP8. It’s an independent circuit from the one that feeds the injectors. The fuel used for lubrication goes through a filter, then to the pump, lubricates the rotating pump internals, exits the pump and goes back to the tank. The fuel that comes into the pumping elements, feeding the rail and the injectors, is a separate circuit. So, fuel going into the pump no longer runs in series, it runs in parallel.
Fuel Injectors
TDR: Why the change in injector style?
Ram/Cummins: As we continue with more stringent emissions regulations, fueling accuracy and pressures become more and more important. The next generation of the fuel injector that has those capabilities (both pressure capabilities and fueling accuracy capabilities). So, that’s really what led to the injector body change and also led us to the top-feed design/packaging. And, we wanted to go to a higher feed injector to make the cylinder head improvements we already spoke about.
TDR: What does the higher rail pressures and top-feed injectors bring to the table?
Ram/Cummins: Essentially what we’re getting is a better atomization of the fuel in the combustion charge. When the fuel is injected, we’re getting a better dispersion of the fuel, creating a cleaner burn and creating more power.
TDR: So, the new injectors give a wider spray pattern and finer atomization for better fuel burn?
Ram/Cummins: Yes, that’s where the pressure component comes from. Going from the 2000 Bar system to the 2200 Bar. Again, the accuracy that this fuel system offers is critical.
Cylinder Head Discussion
TDR: Does the new cylinder head and intake lower EGTs?
Ram/Cummins: Overall, yes. With the improved volumetric flow across the cylinder head it helped with the horsepower number. And our torque curve, while peak torque is at 1,075-pounds, we’ve carried that out and broadened out the torque curve a bit more as well as compared to the previous product.
TDR: The turbo is new. What changes were made there, and why?
Ram/Cummins: It’s the newest generation of Holset’s 300 variable geometry turbo. It looks very similar to the earlier version. But, as we talked about from a packaging standpoint, it’s a whole new unit. There are some subtle changes to it that you can see and then some not-so-subtle changes that you can’t. For instance, on the compressor side it’s actually smaller.
TDR: Is that why driving the 2025 Cummins you don’t notice any turbo lag?
Ram/Cummins: Very observant! This change gives almost instantaneous spool-up time and almost zero turbo lag. And, that ratio of compressor-to-turbine wheel has made the turbo itself more efficient. Then, if you had a chance to peek inside, the turbo actually spins in the opposite direction of the previous turbochargers. This allows for our packaging with the engine-mounted diesel oxidation catalyst (DOC). So, it’s part of the efficiency gains that we’ve talked about.
TDR: Does the 2025 Cummins make more boost than the previous version?
Ram/Cummins: Boost manifold pressure remains the same as in ’24. But, again, due to some of the things we’ve done from the overall airflow improvements, it does it more efficiently. That was one of the biggest reasons for product evolution.
Exhaust System
TDR: Explain the engine-mounted DOC and how the downpipe has changed in 2025.
Ram/Cummins: The exhaust system on the ’25 engine is far different from those used on previous Cummins diesels. We moved the diesel oxidation catalyst (DOC) right up to the turbo, so it lights-off fast and heats up quicker than it would if it were farther downstream (like in the previous engines). That’s better for emissions. Additionally, we went to the close-coupled DOC for better thermal management of the overall after-treatment system. So, to your point, having that catalyst there does give us a better and faster control over the exhaust temperature, which is of course is what’s needed for the diesel particulate filter (DPF) that is a little bit further downstream.
TDR: Explain the changes to the diesel particulate filter (DPF).
Ram/Cummins: I’d say the biggest thing that’s changed on the DPF is that we are now using an external hydrocarbon doser to do the regeneration of the DPF and we’re not as dependent on the upstream components as we once were. So, in that respect, we have the ability to better to improve the soot loading and the soot accumulation on the DPF with this architecture.
TDR: What is the external hydrocarbon doser?
Ram/Cummins: So, during the regeneration cycle we are using a separate nozzle, a seventh injector if you will, that’s spraying diesel fuel in the exhaust stream directly upstream of the DPF to provide the extra fuel for its regeneration. Collectively, putting the DOC closer in the exhaust stream and implementing the doser at the DPF has definitely reduced any DPF clogging concerns.
Glow Plugs, Anyone?
TDR: Why the change to glow plugs in the 2025 Cummins?
Ram/Cummins: The primary motivation to get away from the grid heater was about the wait-to-start time associated with the grid heaters, compared to glow plugs, in sub-zero operating conditions. As an example, think of those emergency vehicles that use a chassis cab. “Wait-to-start” becomes a major concern.
TDR: How fast is the wait-to-start time now with glow plugs?
Ram/Cummins: Changing from a grid heater to glow plugs made a huge difference during cold (below 0 F) weather operation. The start time in cold weather is now around three seconds, where a grid heater in these very low ambient temperatures could take upwards of 30 seconds before engine start. Essentially the new engine is “instant start” even in severe cold operating conditions.
TDR: Has the removal of the grid heater and redesign of the intake manifold improved air flow?
Ram/Cummins: It has. We certainly recognized the flow impact that the grid heater always presented. Being able to take that restriction out of the system was taken advantage of as well.
Ease of Maintenance
TDR: On the maintenance side, how accurate is the 2025 Cummins oil life monitor?
Ram/Cummins: You can absolutely rely on that gauge. It’s not just a timer or something like that. We have spent many, many hours compiling the algorithms that are used to provide a percentage of oil life based on duty cycle. So, oil life indications will vary based on the amount of heavy towing and extreme environments. So, it’s more than just a digital life indicator. It’s a program that’s taking the calculations of the vehicle duty cycle to provide an accurate remaining oil life.
TDR: Is the maximum service interval for oil changes still at 15,000 miles?
Ram/Cummins: Yes. But it is really dependent on the duty cycles and how the truck’s being used and in what conditions. The oil life monitor is a good tool to help the owner in that regard. If anything, we are airing on the slightly conservative side. The last thing we want to do is say the oil does not need to be changed and have someone have a problem.
TDR: Did you achieve your mission with the 2025 Cummins?
Ram/Cummins: Without a doubt. We have a 50-state approval. We’ve improved fuel economy. We improved overall performance. We’ve improved reliability. So, with our new engine, transmission and axle ratio pairing, the 2025 Rams are accelerating faster. For those customers towing in mountainous regions with the 1075-pounds of torque, the truck can maintain speeds up long grades. We can take advantage of the new lower axle ratio (yep, better fuel economy) with our increased number of gears and ratio split.
Bruce Smith
TDR Writer
It was only two weeks ago that the folks at Ram gave members of the press the first ride-and-drive opportunity at their product launch in Laughlin, Nevada. (Think Davis Dam area and the test route for published SAE towing ratings.)
Above: Testing the 2025 Ram HD truck at Davis Dam
TDR writer Bruce Smith was a part of the press group that attended the mid-March product introduction. And, while G.R. Whale gave us a “First Drive” report, Bruce’s report gives us a “First Review” of the 2025 Cummins Engine. Yes, Bruce’s focus was a series of questions that were specific to the Cummins folks at the product launch. The following is his report.
Read the entire discussion below or click HERE to download the file to save, print and/or read later.
THE 2025 CUMMINS 6.7L ENGINE - by Bruce W. Smith
Images courtesy of the author, Ram Truck/Cummins, and Geno’s Garage staff.
It’s been 36 years since the marriage between Cummins and Ram (Dodge) was consummated with the 5.9-liter, 12-valve, 6BT Turbo Diesel being offered in the ¾- and one-ton pickups. Since that time the partnership has evolved as technology and buyer demands have pushed the growth in size, performance and reliability of both trucks and engines to historically new levels. This is exemplified in the 2025 Ram Turbo Diesel 2500, 3500 and Chassis Cab models sporting the High-Output 6.7-liter Cummins, 24-valve engine.
While the original 359 cubic-inch Turbo-Diesel in the 1989 truck delivered 160hp and 400 torque, the new engine sets an industry benchmark making 430hp and class-leading 1,075 torque.
I was able to piece together a little “inside look” at what makes the newest iteration of the 6.7-liter Cummins tick during our short time driving several different models of the new trucks during a Laughlin, Nevada media event.
During that time I interviewed numerous engineers on both the Ram and Cummins teams, about the changes that make this new engine “stronger and more reliable than ever before.” Potential buyers of the heavy-duty 2025 Ram pickups should find the candid answers very informative…
All 2025 Turbo Diesel pickups get 430hp and 1075 torque,
commercial trucks are rated at 360/800.
TDR: What generation would this 2025 version of the Cummins 6.7-liter be called—a Generation 5?
Ram/Cummins: Let’s say Generation 4.5. It’s an evolution of the previous engine into a new type architecture. That’s because there are some significant changes. Yes, it is an inline six. But, it’s a new cast-iron block with a new cylinder head. It has a new air intake manifold. It has new serviceable features with flash-over-the-air capability for calibrations. It has a top-feed loop, fuel filter and dual filtration modules. So there’s a lot that’s changed on this engine.
Editor’s note: I’m going with this nomenclature. Fourth Generation 4.0 = 2010-2012. Then Fourth Generation 4.25 = 2013-2018. Followed by Fourth Generation 4.5, 2019-2024 CGI engine. Now, Fourth Generation 4.75, the new 2025 engine.
TDR: It’s apparent an enormous amount of engineering time and money went into designing this newest generation Cummins. What was the primary goal?
Ram/Cummins: So from our standpoint, the primary goal was to create a more efficient product with lower emissions. A more efficient product from not only the power side, but also in fuel economy gains. When you look at the 3500 truck that is paired with the 8-speed ZF transmission, we’re seeing up to 7% better fuel economy than the 2024s. From the emissions standpoint, this is an architecture that can carry us through on the [EPA] pickup platform [regulations] for quite some time.
TDR: Can you expound on the emissions challenge?
Ram/Cummins: Who knows what’s going to happen with the regulations, but we’re preparing for what we know. This architecture, from an investment standpoint for both Ram and Cummins, made sense for us to move forward with and put into production.
TDR: How did meeting potential future emissions goals lead to some of these new features?
Ram/Cummins: That’s a little complicated to explain. There were simultaneous changes made. There were packaging changes that were made because of emissions. For example, we went with the on-engine, diesel oxidation catalyst (DOC). That required the turbo to shift forward a few inches and it altered the Holset turbine housing. And then we had the new fuel pump (Bosch CP8) and top-feed dry injectors.
Above: Passenger side of the 6.7-liter Cummins. The DOC is now very
close to the turbocharger’s exhaust flange. Also circled, the easy-to-service
oil filter has a removable cap (28mm hex head) and a drop-in filter.
TDR: Did any of these changes make it easier to service this engine compared to the previous model?
Ram/Cummins: Serviceability is definitely improved! Again, the changes in injectors and external fuel lines allowed us to use a top-feed,dual module fuel filter in a drop-in canister with easy access from the top driver’s side of the engine. No more crawling underneath the truck to change the primary fuel filter. Both fuel filters are together for easy access. And, the oil filter: No longer do you have to go through the bottom of the passenger-side wheel well for access to the oil filter. Who wants to create all that mess and pain? The oil filter is also a drop-in element, and owners will really appreciate the ease-of-service these filters provide. Again, our goal with this new design was to deliver a product with more efficiency and better serviceability.
Above: Driver side of the new 6.7-liter Cummins. The fuel filters
are next to each other in the engine compartment. You’ll use the same
28mm hex head socket to remove the fuel filter caps as well as the oil filter cap.
Cylinder Block
TDR: When Cummins introduced the CGI (compacted graphite iron) block in 2019, it was touted as being “stronger, lighter and lower NVH than cast iron.” So why the change? Was returning to a gray cast-iron block a cost savings decision on Ram’s part?
Ram/Cummins: No, I would say that we have over 100 years of experience in gray iron. And when I say “we,” Cummins, across all our platforms, has 100 years of experience in gray iron. We have 30-plus years on the Ram platform. From a cooling standpoint we knew we were going to have to make changes to the [CGI] block. Remember, we’re going to higher horsepower and torque. From a manufacturing and technical kind of expertise we could leverage this for the long-term with the grey iron block easier. It is the right decision for us and this product.
TDR: The 2025 engine has a new block. What’s different from the previous versions?
Ram/Cummins: The biggest change in the new block is mainly in the redesign of the water jackets. Water jackets have been optimized for better flow than the CGI block it replaced. Externally, we kept a lot of the key touch points constant, or close to constant, to minimize the integration impact to Stellantis in the truck’s chassis. But, inside it’s really around the cooling system. We revamped the cooling system to more evenly distribute the coolant flow around the cylinders so we get more uniform cooling front to back than we did with the previous generation(s).
TDR: Can you explain a little how the manufacturing and technical aspects played a role in returning to a gray iron block?
Ram/Cummins: In our case, doing the redesign of the cylinder block we’d used since 2019 meant using all our analytical and design tools. Nothing’s static in time. Since we had to make the design changes to the block for emissions and cooling improvements, we took the opportunity to apply the latest analysis and design tools to do it. We saw the path to get back to gray iron and keep the overall package in a similar overall weight standpoint while reaping all the benefits that gray iron has from the ease-of-manufacturing standpoint.
TDR: Is gray iron easier to work with than CGI?
Ram/Cummins: When it comes to the manufacturing and the machining of cast iron versus CGI, in an overall quality play, CGI is a pretty tough material to machine and to deal with. And as far as residual burrs, machining debris, and keeping things of that nature out, gray cast iron lends itself to an overall higher quality and fewer debris-related issues that we’ve experienced at our machining facility.
Engine Internals
TDR: Were there changes in the pistons, crankshaft, rods and bearings?
Ram/Cummins: Sure, but those changes are subtle on the rotating assembly. The pistons were redesigned to optimize the new fuel injectors.
TDR: How has the cylinder head been changed?
Ram/Cummins: The same thought carried through with the cylinder head, better cooling. The compression ratio is the same as before (16.2:1), but we took the opportunity to change the valve spacing because we had that luxury this time to be able to do that, which allowed us to install bigger intake valves and bigger exhaust valves. The intake and the cylinder head as a whole is a complete and total redesign.
TDR: The intake manifold is totally different from the earlier engines, correct?
Ram/Cummins: Yes. We divorced the intake manifold from the previous generation. That change worked hand-in-hand with the new fuel system that I’m sure we’ll touch on here in a bit. Plus, moving from the side-feed injectors of the previous generation to the top-feed we use now, gave us the opportunity to put more optimized and larger intake and exhaust ports in the cylinder head (previously mentioned) to help overall volumetric efficiency. And then there’s a new mass airflow sensor housing and mass airflow sensor on that intake, which relates back to the efficiency play.
TDR: Did these changes play a big part in better fuel economy and that 10hp boost in horsepower?
Ram/Cummins: Yes. When overall volumetric efficiency improved, so did those numbers for speed on grade, and now the 430hp and 1075ft-lbs are available across both the 2500 and 3500. All pickup customers now have access to this rating.
Fuel Injection Pump
TDR: Now to the question that most diesel owners want to know: What is a Bosch “CP8” fuel injection pump that’s used on the new engine?
Ram/Cummins: We needed much higher fuel pressures for this new fuel system. We moved from 32,000 PSI (2,000 Bar) to 39,000 PSI (2,200 Bar). So, some significant improvements and increases were needed in the fuel injection pump. That’s what made us consider a new fuel pump design.
TDR: The CP8 looks identical to the CP4.2. But it’s different inside?
Ram/Cummins: Correct. While the CP8 may look the same, the internals are different with improved pumping and roller elements along with isolated-loop fuel lubrication. In partnership with Bosch and with Stellantis, this pump has gone through significant testing and vast improvements. We’ve developed new tests that not only helped revalidate the older CP3 that has been used since 2003, but also helped validate the new CP8. The tests are run with out-of-specification conditions to ensure we are validating beyond what coud be seen in application.
Above: The “isolated loop” fuel lubrication lines (blue “tick-marks”)
are easily identified in the picture of the CP8.
TDR: I understand one of the validation tests of the CP8 was called the “Killer Test” where the pump was fed worst-case fuel (with contaminants) under the worst conditions, testing the pump until it failed. Can you elaborate?
Ram/Cummins: The test is run with out-of-specification fuels, out-of-specification fuel temperatures, as well as pump speeds and pressures that are not possible in application. The equivalent of operating for thousands of miles under the most severe temperatures with the poorest of fuel. It was created to ensure that the fuel pump in a Ram would have the robustness and durability that Cummins is known for.
TDR: What re-engineering resulted from this broader, much more intensive validation testing of the CP8?
Ram/Cummins: The Bosch CP8 is a new fuel pump. The roller and shoe design that was in the old pump has been redesigned to a pinned roller-tappet architecture. Another major difference is the lubrication circuit of the CP8. It’s an independent circuit from the one that feeds the injectors. The fuel used for lubrication goes through a filter, then to the pump, lubricates the rotating pump internals, exits the pump and goes back to the tank. The fuel that comes into the pumping elements, feeding the rail and the injectors, is a separate circuit. So, fuel going into the pump no longer runs in series, it runs in parallel.
Fuel Injectors
TDR: Why the change in injector style?
Ram/Cummins: As we continue with more stringent emissions regulations, fueling accuracy and pressures become more and more important. The next generation of the fuel injector that has those capabilities (both pressure capabilities and fueling accuracy capabilities). So, that’s really what led to the injector body change and also led us to the top-feed design/packaging. And, we wanted to go to a higher feed injector to make the cylinder head improvements we already spoke about.
TDR: What does the higher rail pressures and top-feed injectors bring to the table?
Ram/Cummins: Essentially what we’re getting is a better atomization of the fuel in the combustion charge. When the fuel is injected, we’re getting a better dispersion of the fuel, creating a cleaner burn and creating more power.
TDR: So, the new injectors give a wider spray pattern and finer atomization for better fuel burn?
Ram/Cummins: Yes, that’s where the pressure component comes from. Going from the 2000 Bar system to the 2200 Bar. Again, the accuracy that this fuel system offers is critical.
Cylinder Head Discussion
TDR: Does the new cylinder head and intake lower EGTs?
Ram/Cummins: Overall, yes. With the improved volumetric flow across the cylinder head it helped with the horsepower number. And our torque curve, while peak torque is at 1,075-pounds, we’ve carried that out and broadened out the torque curve a bit more as well as compared to the previous product.
TDR: The turbo is new. What changes were made there, and why?
Ram/Cummins: It’s the newest generation of Holset’s 300 variable geometry turbo. It looks very similar to the earlier version. But, as we talked about from a packaging standpoint, it’s a whole new unit. There are some subtle changes to it that you can see and then some not-so-subtle changes that you can’t. For instance, on the compressor side it’s actually smaller.
TDR: Is that why driving the 2025 Cummins you don’t notice any turbo lag?
Ram/Cummins: Very observant! This change gives almost instantaneous spool-up time and almost zero turbo lag. And, that ratio of compressor-to-turbine wheel has made the turbo itself more efficient. Then, if you had a chance to peek inside, the turbo actually spins in the opposite direction of the previous turbochargers. This allows for our packaging with the engine-mounted diesel oxidation catalyst (DOC). So, it’s part of the efficiency gains that we’ve talked about.
TDR: Does the 2025 Cummins make more boost than the previous version?
Ram/Cummins: Boost manifold pressure remains the same as in ’24. But, again, due to some of the things we’ve done from the overall airflow improvements, it does it more efficiently. That was one of the biggest reasons for product evolution.
Exhaust System
TDR: Explain the engine-mounted DOC and how the downpipe has changed in 2025.
Ram/Cummins: The exhaust system on the ’25 engine is far different from those used on previous Cummins diesels. We moved the diesel oxidation catalyst (DOC) right up to the turbo, so it lights-off fast and heats up quicker than it would if it were farther downstream (like in the previous engines). That’s better for emissions. Additionally, we went to the close-coupled DOC for better thermal management of the overall after-treatment system. So, to your point, having that catalyst there does give us a better and faster control over the exhaust temperature, which is of course is what’s needed for the diesel particulate filter (DPF) that is a little bit further downstream.
TDR: Explain the changes to the diesel particulate filter (DPF).
Ram/Cummins: I’d say the biggest thing that’s changed on the DPF is that we are now using an external hydrocarbon doser to do the regeneration of the DPF and we’re not as dependent on the upstream components as we once were. So, in that respect, we have the ability to better to improve the soot loading and the soot accumulation on the DPF with this architecture.
TDR: What is the external hydrocarbon doser?
Ram/Cummins: So, during the regeneration cycle we are using a separate nozzle, a seventh injector if you will, that’s spraying diesel fuel in the exhaust stream directly upstream of the DPF to provide the extra fuel for its regeneration. Collectively, putting the DOC closer in the exhaust stream and implementing the doser at the DPF has definitely reduced any DPF clogging concerns.
Glow Plugs, Anyone?
TDR: Why the change to glow plugs in the 2025 Cummins?
Ram/Cummins: The primary motivation to get away from the grid heater was about the wait-to-start time associated with the grid heaters, compared to glow plugs, in sub-zero operating conditions. As an example, think of those emergency vehicles that use a chassis cab. “Wait-to-start” becomes a major concern.
TDR: How fast is the wait-to-start time now with glow plugs?
Ram/Cummins: Changing from a grid heater to glow plugs made a huge difference during cold (below 0 F) weather operation. The start time in cold weather is now around three seconds, where a grid heater in these very low ambient temperatures could take upwards of 30 seconds before engine start. Essentially the new engine is “instant start” even in severe cold operating conditions.
TDR: Has the removal of the grid heater and redesign of the intake manifold improved air flow?
Ram/Cummins: It has. We certainly recognized the flow impact that the grid heater always presented. Being able to take that restriction out of the system was taken advantage of as well.
Ease of Maintenance
TDR: On the maintenance side, how accurate is the 2025 Cummins oil life monitor?
Ram/Cummins: You can absolutely rely on that gauge. It’s not just a timer or something like that. We have spent many, many hours compiling the algorithms that are used to provide a percentage of oil life based on duty cycle. So, oil life indications will vary based on the amount of heavy towing and extreme environments. So, it’s more than just a digital life indicator. It’s a program that’s taking the calculations of the vehicle duty cycle to provide an accurate remaining oil life.
TDR: Is the maximum service interval for oil changes still at 15,000 miles?
Ram/Cummins: Yes. But it is really dependent on the duty cycles and how the truck’s being used and in what conditions. The oil life monitor is a good tool to help the owner in that regard. If anything, we are airing on the slightly conservative side. The last thing we want to do is say the oil does not need to be changed and have someone have a problem.
TDR: Did you achieve your mission with the 2025 Cummins?
Ram/Cummins: Without a doubt. We have a 50-state approval. We’ve improved fuel economy. We improved overall performance. We’ve improved reliability. So, with our new engine, transmission and axle ratio pairing, the 2025 Rams are accelerating faster. For those customers towing in mountainous regions with the 1075-pounds of torque, the truck can maintain speeds up long grades. We can take advantage of the new lower axle ratio (yep, better fuel economy) with our increased number of gears and ratio split.
Bruce Smith
TDR Writer
