The 3.9L Cummins 4BT was an inline 4-cylinder turbocharged diesel engine that was introduced in 1984. This small-scale Cummins engine was designed with simplicity and durability in mind. The 3.9L 4BT Cummins was initially created for agricultural, industrial, and light-duty commercial use. This engine received the nickname the “bread truck” because it was frequently used in delivery trucks. Many components from the 12 valve 6BT Cummins were shared with this engine including the solid foundation of a cast-iron block, internal engine components, and a direct injection fuel system. The lack of electronic controls in this engine also provided increased reliability and simplicity.

Similar to the 12 Valve 6BT Cummins, the 4BT Cummins had an overhead valve design with 2 valves per cylinder and a forged-steel crankshaft. The 3.9L Cummins was constructed with a cast-iron block and cylinder head capable of enduring the harshest conditions. This engine contained cast-aluminum pistons and forged-steel connecting rods to handle increased cylinder pressure. For more efficient combustion the 4BT Cummins utilized a direct injection fuel system with a gear-driven injection pump. The highly reliable Bosch P7100 injection pump was paired with mechanical injectors that sprayed fuel directly into the combustion chamber. Fitted to the 3.9L Cummins was a Holset fixed-geometry turbocharger that was completely mechanical, which reduces failure points. The simplicity and reliability of this engine makes it a popular choice for diesel engine swap projects on Jeeps, SUVs, and small pickups. The 4BT Cummins can be paired with a variety of different transmissions which makes diesel swapping different vehicles even easier. In addition, this engine was relatively small compared to other diesel engines at the time, with dimensions of 30.6” in length, 24.6” wide, and 37.7” tall.

Cummins diesel engines are typically known to be fuel efficient and this 4-cylinder turbo diesel was no exception, by delivering almost 21 mpg in certain applications. A stock 3.9L Cummins 4BT was rated at 105 hp and 265 lb-ft of torque, but much like the 12 valve 5.9L Cummins its built to handle increased power. In 1994 the 3.9L Cummins 4BT engine was discontinued, but many of these engines are still readily available. XDP carries parts and accessories from hundreds of the top manufacturers to ensure you have the parts necessary to keep your 3.9L Cummins running the way it should. Find all the diesel performance parts your 4BT Cummins engine needs at XDP.