A Cummins swap means installing a Cummins inline-six diesel, usually a 5.9L or 6.7L from a Dodge or Ram pickup, in a truck that did not come with one. The 12 valve 5.9 is the traditional choice because its injection is mechanical, while later 24 valve and common rail engines depend on electronics. Weight, cooling, transmission and emissions rules all need to be planned before you start.
What is a Cummins swap?
Cummins diesels powered Dodge and Ram heavy-duty pickups starting with the 1989 model year. The engines are long, tall and heavy compared with the gas V8s most trucks came with, but they are known for torque and durability, which is why people swap them into other trucks for towing and long service. Our Cummins vs Duramax vs Powerstroke guide compares the main diesel families.
Which Cummins is easiest to swap?
- 12 valve 5.9 (1989 to 1998 in Dodge trucks): mechanical fuel injection, so it can run without an engine computer. That simplicity is why it is the traditional swap engine.
- 24 valve 5.9 (1998.5 to 2002): still relatively simple, but its injection pump is electronically controlled, so it needs its wiring and control module.
- Common rail 5.9 and 6.7 (2003 onward): fully electronic. They need the engine computer, the full wiring harness and the sensors, and they are often designed to communicate with other modules in the donor truck. Newer engines also came with more emissions equipment.
Our 12 valve vs 24 valve vs common rail guide explains these generations in more detail.
Main systems in a Cummins swap
Engine mounts
Swap-specific mounts or fabricated brackets are needed to place the engine in the new frame. Check firewall, radiator support and hood clearance, since the inline-six is long and tall.
Weight, suspension and brakes
A Cummins adds substantial weight over the front axle compared with most gas engines. Front springs, steering and brakes should be checked, and often upgraded, to handle the extra load and the heavier trailers many owners plan to pull.
Cooling and intercooler
A diesel working hard makes a lot of heat, so the radiator must be sized for it. Turbocharged, intercooled versions also need room in front of the radiator for the intercooler and a clear path for its piping.
Fuel system
The truck needs a fuel supply set up for diesel: a suitable tank and lift or supply pump, filtration and the return line the engine expects. A fuel system built for a gasoline engine is not a substitute.
Exhaust
Plan the turbo outlet and downpipe routing around the frame and steering. Keep every emissions component the engine came with in the exhaust system.
Transmission and adapter
The Cummins bellhousing pattern differs from GM and Ford gas engines, so you either use a transmission that was originally paired with the Cummins or an adapter made for your transmission. Check that the transmission is rated for diesel torque.
Driveshaft, electrical and gauges
The driveshaft length usually changes. Cummins-powered Ram trucks came with two batteries, and the charging and starting system needs to be sized for a diesel. Most swappers add gauges for boost, exhaust gas temperature, coolant temperature and oil pressure so they can watch the engine under load.
Emissions rules come first
Rules vary by state, and some states are much stricter than others. Many emissions programs expect a swapped engine to be the same model year or newer than the vehicle and to keep all of its original emissions equipment, including the exhaust aftertreatment that newer diesels use, such as a diesel particulate filter and, on later engines, a system that uses diesel exhaust fluid. Never plan a swap around removing emissions equipment. Check your state’s current rules before you buy an engine or start the work; this guide does not say whether a particular swap is legal.
Cummins engines we carry
The D&J short blocks, long blocks and engines we carry are made for 2003-and-later common rail Ram trucks, covering the 5.9 and the 6.7. We do not carry 12 valve or 24 valve engines. Browse Cummins 5.9 and 6.7 blocks and engines or the 5.9 Cummins engines page, and confirm the exact model year range with a parts specialist before ordering.
More guides: 5.9 vs 6.7 Cummins · Cummins swap transmission options.
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