6.7 Cummins Diesel Engine Guide

Since it first became available for the 2007 model year, the 6.7 Cummins has made a solid name for itself as one of the most powerful and dependable turbo-diesel truck engines. Over the years there have been a number of design changes and problems to be aware of, however.

In this guide we are going to cover everything about the 6.7 Cummins. Starting with its history, specs, and technical details and then moving into common problems and performance modifications.

6.7L Cummins History

The 6.7 Cummins debuted in the 2007 model year inside the Dodge Ram 2500 & 3500 Heavy Duty trucks and Chassis Cab 3500, 4500, and 5500 Commercial trucks. Ford also made the engine an option inside their F-650 & F-750 Medium Duty trucks.

Over the years, the engine has varied in power levels (see below), but inside the Ram Heavy Duty trucks it has produced 350-420 horsepower and 610-1,075 lb-ft of torque. Inside the Ram commercial trucks, it made 305-360 horsepower and 610-800 lb-ft of torque, and in the Fords it made 200-360 horsepower and 520-800 lb-ft of torque. 

The ISB 6.7 has made a name for itself as being both reliable and capable of extreme performance. It is the successor to the 5.9 Cummins, which Dodge put inside their Ram trucks for almost two decades starting in the late-’80s. The 6.7 is now coming up on its own two-decade production run, and it is still looking as strong as ever. Currently, Ram is the only user of the engine, and they put it inside their Heavy Duty 2500 & 3500 trucks. 

In 2011, Cummins introduced a high-output version of the engine for the Ram 3500 Heavy Duty models only. The high-output version bumped up both horsepower and torque, and was only available with the 68RFE automatic transmission. In 2013, the Aisin AS69RC automatic replaced the 68RFE as the only option for the HO 6.7L Cummins. As of 2024, Cummins still produces the high-output version of the 6.7, which makes 420 horsepower and 1,075 lb-ft of torque. 

Engine Specs

Engine	6.7 Cummins
Engine Family	Cummins ISB
Model Years	2007-2024
Displacement	6.7 liters (407.5 cid)
Aspiration	Turbocharged: Holset HE351VE VGT
Configuration	Inline-6
Compression Ratio	2007-2018 – 17.3:1 2019+ – 19.0:12019+ HO – 16.2:1
Bore and Stroke	107mm x 124mm (4.21 in x 4.88 in)
Valve Train	Overhead Valve (OHV), 24-valve (4 val/cyl)
Variable Valve Timing	No
Fuel System	Direct Injection, Bosch CP3 & CP4.2 (2019-2020 only)
Head Material	Cast Iron
Block Material	Gray Cast Iron (2007-2018); Compacted Graphite Iron (2019+)
Horsepower Output	200-420 horsepower
Torque Output	520-1,075 lb-ft

Engine Design Basics

The 6.7 Cummins is a 6.7 liter (407.5 cid) inline-6, turbo-diesel engine. From 2007–2018, Cummins used a gray cast iron cylinder block, but changed to compacted graphite iron (CGI) starting in 2019. The CGI block helped shave more than 50 pounds off the engine’s dry weight. The cylinder head has always been cast iron since 2007. The bore and stroke are 107 mm x 124 mm (4.21 in x 4.88 in), making the engine undersquare. 

For its duration, Cummins has used cast aluminum pistons inside the 6.7. From 2007–2018, the connecting rods were powdered metal, but for 2019+ are forged alloy steel. Compression sat at 17.3:1 from 2007–2018. It increased to 19.0:1 for the standard output versions in 2019, but decreased to 16.2:1 for the high-output version the same year. 

Turbocharger and Fuel System

The 6.7 Cummins has always used the same blower, a Holset HE351VE Variable Geometry Turbocharger (VGT). VGT turbochargers have been around since the late 1990s, and use a sliding nozzle ring that helps allow for a wide flow range. This allows for better fuel efficiency, reduced emissions, and increased performance

According to Cummins, “The Holset VGT is unique because the vanes slide axially so it has fewer moving parts and less wear sites. This improves the durability and reliability.” For cooling, the turbo-system uses a large air-to-air intercooler. Generally, it runs about 20-25 PSI of boost under max load, but varies depending on fuel quality and atmospheric conditions. 

For the fuel system, the 6.7L Cummins uses direct injection, high-pressure, common rail. From 2007–2018, Cummins used the Bosch CP3 fuel pump that was capable of 26,000 PSI max injection pressure. From 2019–2020, they switched to the Bosch CP4.2 pump that made up to 29,000 PSI of injection pressure. However, the CP4.2 proved to be very faulty, and Cummins returned to using the CP3 starting again in 2021. 

Valve Train

The valve train is a mix of both old-school and new-school. It has a traditional pushrod actuated, overhead-valve train (OHV) with a single in-block camshaft. However, the 6.7 Cummins doesn’t use 2 valves/cylinder, but actually uses 4 valves to make it a 24-valve motor. The pushrods actuate 4-valves per cylinder (2 intake/2 exhaust) instead of just 2, which helps improve efficiency and performance. 

From 2007–2018, the lifters were solid, but for 2019+ Cummins has switched to more efficient hydraulic lifters. The valve lash clearance for the intake valves measure to 0.010 inches, and the exhaust valves are 0.020 inches. The pre-2018 engines required valve adjustments after 150,000 miles, but the 2019+ engines do not require any adjustments. 

Emissions Systems

The 6.7 Cummins uses a complicated emissions system that involves several different systems working together. The first is the exhaust gas recirculation (EGR) system, which recirculates post-DPF exhaust gasses back into the intake manifold. This way they can re-enter the combustion chamber to be reburned again instead of getting released to the atmosphere. The next is the diesel oxidation catalyst (DOC) and is part of the exhaust. The DOC is basically a catalytic converter that is designed specifically to work with diesel emissions. 

The engine also uses a diesel particulate filter (DPF), which helps reduce and eliminate diesel soot. The DPF collects soot and burns it off through either active or passive regeneration. Passive regeneration happens from normal driving, while active regeneration happens from injecting diesel fluid into the DOC. From 2007–2012, the DOC and DPF systems were separate. However, beginning in 2013, Cummins merged the two together. 

From 2007–2012, the Cummins also used a NOx Abosrption Catalyst (NAC). The NAC helped absorb nitrogen oxide, and in 2013 Cummins replaced the NAC with a new selective catalyst recirculation system (SCR). The SCR is more efficient, and uses diesel exhaust fluid (DEF) to help control and reduce emissions. 

6.7 Cummins Reliability and Problems

Overall, the 6.7 Cummins is a reliable engine. However, that does come with a few caveats. Compared with its predecessor, the 5.9 Cummins, it’s actually less reliable. This is mainly due to the addition of several emissions features. While the emissions filters do help reduce pollution, they have also been shown to be problematic and prone to failure. 

The biggest issue with the emissions parts failure is their high cost. Considering most diesel owners do not want them on their trucks in the first place, paying hundreds if not thousands in repair costs is extremely unwelcome. In addition, considering you can delete most of the emissions equipment with a tune for about the same price, many owners go that route instead.

Still, the Cummins 6.7 — aside from the emissions issues — is a very robust and stout engine. It has a B10 life (or point where 10% of the engines will fail) of 250,000 miles, while the B50 life is at 350,000 miles. Considering Cummins has been producing the engine since 2007 and it is still in production today, that’s a pretty good endorsement for reliability. 

However, the engine is far from perfect, and there are a few common problems in addition to the emissions issues. Previously, we looked at the 5 most common ISB 6.7 Cummins engine problems, so we’ll just summarize them here. We also have a YouTube video below summarizing the issues. 

Common Problems

• Clogged DPF
• Turbo failure
• Head gasket failure
• Fuel dilution
• Cracked EGR cooler

The most common 6.7L Cummins problem is a clogged DPF. The DPF is part of the exhaust and emissions systems, and it burns exhaust soot. However, it can easily become clogged, which kills performance and increases heat. As long as you are under warranty the cost isn’t bad, but paying out of pocket is easily $1,000 minimum. 

The Holset HE351VE turbo is also prone to failure, especially around the turbo seals. Many turbos have gone bad in as little as 120,000 miles. Replacements are also expensive, and many people opt for a larger turbo as a replacement swap. 

Head gasket and fuel dilution problems can also present themselves, especially with mods and/or excessive idling. The final problem is EGR cooler failure. The EGR cooler helps reduce the temperature of exhaust gasses before they are routed back into the intake manifold. They are highly prone to failure, which can hurt the entire EGR system. Like the DPF, many people simply delete their EGR-systems if they fail instead of replacing them. 

6.7 Cummins Performance Potential

Now let’s talk about the best part of the 6.7 Cummins: performance and modding. From the factory, inside the 2023 Ram Heavy Duty, the standard output Cummins makes 370 horsepower and 850 lb-ft of torque. For the HO Cummins, that jumps to 420 horsepower and an incredible 1,075 lb-ft of torque. 

This equates to a max payload of 6,120 pounds and a max towing capacity of 34,650 pounds for the HO Cummins. For the standard Cummins, the payload increases to 6,390 pounds, but the towing capacity drops to 22,220 pounds. Both of them beat the larger displacement 6.4 HEMI V8, which has a max towing capacity of 17,750 pounds. 

Bolt-on Performance Upgrades

• Tuning
• Cold Air Intake upgrade
• Exhaust upgrade
• Intercooler upgrade
• Intake horn upgrade

Best Performance Mods

While the 6.7 ISB Cummins already has some outstanding performance, you can always get even more with some basic bolt-on mods and tuning. Previously, we looked at the top 5 best 6.7 Cummins performance mods. We’ll just summarize here, so make sure to check out the article for the full breakdown.

First up is tuning. Tuning the 6.7 Cummins is by far the most cost effective way to add gobs of horsepower and torque without making any bolt-on changes. With just a tune, you can add up to 175 wheel-horsepower. There are many different tuning options, and we suggest using EFI Live and going with a reputable local tuner.

After tuning, a cold air intake is the next upgrade. With our own Boosted Performance’s 4” open intake you can up to 10 wheel-horsepower and 30 wheel-torque in gains. The BP intake uses a larger S&B style filter and really outflows the stock unit. Check out our intake guide for even more recommendations. 

Next up are exhaust upgrades. Upgrading the downpipe is a great way to reduce back pressure and free up lots of extra horsepower and torque. You can check out our 6.7L Cummins downpipe guide for the best downpipe recommendations. 

After the exhaust, we’d suggest looking into a bigger intercooler. The intercooler cools down the post-turbo charged air, and the stock intercooler is very undersized for heavy duty use. A larger intercooler will reduce intake temperatures, which increases and sustains performance under prolonged use. 

Finally, upgrading the intake horn is a solid mod. Upgrading the horn will lower exhaust gas temperature (EGT) and increase airflow, resulting in 15-20 wheel-horsepower and torque gains. Check out our 6.7 Cummins intake horn upgrade guide for the top recommendations. 

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