ISB 6.7 Cummins engine
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6.7 Cummins Diesel Engine Guide

Chandler Stark

Meet Chandler

Chandler is an automotive expert that joined the DieselIQ and 8020 Media teams in 2022. He’s been working on and modifying cars from a young age and has a passion for JDM builds. However, Chandler is also a big fan of American muscle & diesel trucks. He delivers endless automotive knowledge and hands-on experience, and is a seasoned writer who spends some of his free time writing for The Grunge.

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. The engine has 6.7 liters of displacement and is a traditional inline-6 style motor. Depending on the year and model, the 6.7L Cummins produces 200-420 horsepower and 520-1,075 lb-ft of torque. It has both above average reliability and above average performance all wrapped up in a fantastic package. Read on to find out all about the 6.7 liter Cummins ISB turbo-diesel. 

Make sure to check out our other ISB 6.7 Cummins content, including: 5 most common ISB 6.7 Cummins engine problems, 6.7 Cummins intake horn upgrades, 6.7 L Cummins downpipe upgrades, 6.7 L Cummins emissions systems guide, 6.7 Cummins DPF delete guide, 6.7 Cummins best performance mods, ISB 6.7L Cummins cold air intake upgrades, and ISB 6.7 L Cummins tuning guide.

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. It has many nicknames, the 6.7 Cummins ISB, 6.7 ISB, ISB 6.7, or just the 6.7 Cummins. The ISB stands for Interact System B, which means it uses electronic controls and is a Cummins B-series engine.

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. 

6.7 Cummins Specs

Engine6.7 Cummins
Engine FamilyCummins ISB
Model Years2007-2024
Displacement6.7 liters (407.5 cid)
AspirationTurbocharged: Holset HE351VE VGT
Compression Ratio2007-2018 – 17.3:1 2019+ – 19.0:12019+ HO – 16.2:1 
Bore and Stroke107mm x 124mm (4.21 in x 4.88 in) 
Valve TrainOverhead Valve (OHV), 24-valve (4 val/cyl)
Variable Valve TimingNo
Fuel SystemDirect Injection, Bosch CP3 & CP4.2 (2019-2020 only)
Head MaterialCast Iron
Block MaterialGray Cast Iron (2007-2018); Compacted Graphite Iron (2019+)
Horsepower Output200-420 horsepower
Torque Output520-1,075 lb-ft

6.7 Cummins Vehicles

The 6.7 Cummins turbo-diesel appeared in the following vehicles:

  • 2007–2024 Dodge/Ram 2500 & 3500 Heavy Duty Trucks
  • 2007–2021 Dodge/Ram Chassis Cab 3500, 4500, & 5500 Commercial Trucks
  • 2007–2015 Ford F-650 & F-750 Medium Duty Trucks

2007–2024 Dodge/Ram 2500 & 3500 Heavy Duty Trucks (350-385 horsepower, 610-1,075 lb-ft)

  • 2007–2010 Dodge Ram 2500 & 3500
    • 350 horsepower, 650 lb-ft (68RFE Auto Transmission)
    • 350 horsepower, 610 lb-ft (G56 Manual Transmission)
  • 2011–2012 Ram 2500 & 3500
    • 350 horsepower, 610 lb-ft (G56 Manual Transmission)
  • 2011–2012 Ram 3500 (High Output)
    • 350 horsepower, 800 lb-ft (68RFE Auto Transmission)
  • 2013–2018 Ram 2500 & 3500
    • 350 horsepower, 660 lb-ft (G56 Manual Transmission)
    • 370 horsepower, 800 lb-ft (68RFE Auto Transmission)
  • 2013–2014 Ram 3500 (High Output)
    • 385 horsepower, 850 lb-ft (Aisin AS69RC Auto Transmission)
  • 2015 Ram 3500 (High Output)
    • 385 horsepower, 865 lb-ft (Aisin AS69RC Auto Transmission)
  • 2016–2017 Ram 3500 (High Output)
    • 385 horsepower, 900 lb-ft (Aisin AS69RC Auto Transmission)
  • 2018 Ram 3500 (High Output)
    • 385 horsepower 930 lb-ft (Aisin AS69RC Auto Transmission)
  • 2019–2024 Ram 2500 & 3500
    • 370 horsepower, 850 lb-ft (68RFE Auto Transmission)
  • 2019–2020 Ram 3500 (High Output)
    • 400 horsepower, 1,000 lb-ft (Aisin AS69RC Auto Transmission)
  • 2021–2024 Ram 3500 (High Output)
    • 420 horsepower, 1,075 lb-ft (Aisin AS69RC Auto Transmission) 

2007–2021 Dodge Ram Chassis Cab 3500, 4500, 5500 Commercial Trucks (305-360 horsepower, 610-800 lb-ft)

  • 2007–2012 Dodge Ram Chassis Cab 3500, 4500, 5500
    • 305 horsepower, 610 lb-ft (Aisin AS69RC Auto/G56 Manual Transmissions)
  • 2013–2019 Dodge Ram Chassis Cab 3500, 4500, 5500
    • 320 horsepower, 650 lb-ft (G56 Manual Transmission)
    • 325 horsepower, 750 lb-ft (Aisin AS69RC Auto Transmission)
  • 2020–2021 Dodge Ram Chassis Cab 3500, 4500, 5500
    • 360 horsepower, 800 lb-ft (Aisin AS69RC Auto Transmission)

2007–2015 Ford F-650 & F-750 Medium Duty Trucks (200-360 horsepower, 520-800 lb-ft)

  • 2007–2015 Ford F-650 and F-750
    • 200 horsepower, 520 lb-ft
    • 220 horsepower, 520 lb-ft
    • 240 horsepower, 560 lb-ft
    • 250 horsepower, 660 lb-ft
    • 260 horsepower, 660 lb-ft
    • 280 horsepower, 660 lb-ft
    • 300 horsepower, 660 lb-ft
    • 325 horsepower, 750 lb-ft
    • 340 horsepower, 660 lb-ft
    • 360 horsepower, 800 lb-ft

6.7 Cummins Engine Design Basics

6.7 ISB Cummins
6.7 ISB Cummins

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. 

6.7 L Cummins Turbocharger and Fuel System

The Cummins 6.7 ISB 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. 

6.7 L Cummins Valve Train

The Cummins 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 ISB 6.7 required valve adjustments after 150,000 miles, but the 2019+ engines do not require any adjustments. 

6.7L Cummins 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. 

Make sure to check out our 6.7L Cummins Emissions Systems Guide for an even more in-depth breakdown.

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 for the ISB 6.7. 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 6.7 Cummins 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. 

6.7L Cummins Common Problems

The top 5 most common ISB 6.7 problems are:

  • 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 and Top Mods

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. 

6.7L Cummins Bolt-on Mods

Top 5 ISB 6.7 Cummins performance mods:

  • Tuning
  • Cold Air Intake upgrade
  • Exhaust upgrade
  • Intercooler upgrade
  • Intake horn upgrade
6.7 ISB Cummins
6.7 ISB Cummins

Best ISB 6.7 Cummins Bolt-Ons

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 affiliate 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 ISB 6.7 Cummins 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. 

6.7 Cummins FAQ

Is the 6.7 liter Cummins a good motor?

Yes. The 6.7 Cummins is a solid and reliable motor that is capable of some jaw dropping performance. From the factory, the high-output ISB Cummins produces 420 horsepower and 1,075 lb-ft of torque.

Is the 6.7 Cummins a 6 or 8 cylinder?

The 6.7 Cummins is a 6 cylinder inline-6 engine. Even though it is only 6 cylinders, the high-output ISB 6.7 Cummins still produces 420 horsepower and 1,075 lb-ft of torque.

What is the horsepower of a 6.7 Cummins?

For 2024, the 6.7 Cummins puts out 370 horsepower and 850 lb-ft of torque in standard form, or 420 horsepower and 1,075 lb-ft of torque in the high-output version.

What are the cons of a 6.7 Cummins?

The main drawbacks to the 6.7 Cummins are the emissions systems. These hurt performance and diminish reliability. Without the emissions systems, the 6.7 Cummins might have been one of the top turbo-diesel engines ever made.

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