Comprehensive 3.9L 4BT Cummins specification

Time: Dec 20, 2022

Comprehensive 3.9L 4BT Cummins specification

4BT Cummins Engine

3.9L 4BT Cummins Engine that is going into a Nissan Patrol GQ SUV

One of the most common Diesel engines used on diesel conversions is the 3.9L 4BT Inline 4-cylinder Cummins engine. It’s extreme durable like its 6BT relative but it takes up significantly less space. We see a ton of 4BT engines swapped into Jeeps, SUVs, and even cars. In addition to their small size, the 3.9L 4BT Cummins diesel engine offers other advantages as well, such as impressive performance specs and the ability to last hundreds of thousands of miles. They’re also fairly easy to locate!

3.9L 4BT Cummins Engine Design

The 3.9L 4BT Cummins is a diesel turbocharged engine that utilizes an inline 4-cylinder design. The acronym, 4BT, means four-cylinder, “B” series turbocharged. It shares many of the same components as the 6BT Cummins, the 12-Valve 5.9L Cummins engine found in the 1st Generation Cummins. In fact, if you take away two cylinders you almost have the same engine.

The 4BT engine uses the same pistons, connecting rods, injectors, injection pump and valvetrain as the famous 12V Cummins. Both the engine block and the cylinder head are made of cast iron. This results in a durable foundation capable of withstanding serious abuse. When the 4BT Cummins was released in 1983, it featured 2 valves per cylinder, for a grand total of 8 valves. After 1998, these engines used a four valve per cylinder design, for a total of 16 valves. This is one of the updates that helped second generation 4BTA Cummins engines produce greater performance specs.

4BT Reliability

Just like the 6BT 12-Valve 5.9L Cummins Engine, the 4BT is rock solid. It is overbuilt, especially for its size. They also last an extremely long time. It’s also essentially service free thanks to the fact that it is gear-driven. Its camshaft, oil pump, injection pump, and accessory drive systems are all gear-driven, meaning there is no timing belt or chain. Early 4BT engines (Pre-1998) also lack electronics, adding to their reliability and simplicity.

4BT Cummins Performance

The 4BT Cummins Engine was originally designed for agricultural, industrial, and light commercial applications. First generation 3.9L 4BT Cummins Diesel engines produce 105 horsepower and 265 lb-ft of torque. Second generation engines, known as 4BTA engines, use 4 valves per cylinder, and produce higher performance numbers. The most common iterations of the 4BTA Cummins Diesel engine produce 170 horsepower and 420 lb-ft of torque.

The 4BT Cummins Engine was way ahead of its time when it was released in the ’80s. It uses direct fuel injection, turbocharging, and an inline-4 design to provide impressive performance specs and fuel efficiency in a tiny package. The only down side of the 4BT is that it runs relatively rough when compared to 6BT engines. This is because the 4BT isn’t balanced, meaning it’s prone to a lot of vibration.

4BT Cummins-powered Jeep Wrangler built by Kyle Martin.

Upgrading Performance

While these numbers are a fraction of what the 12V or 24V Cummins engines produce from the factory, these numbers can go up quick! This is especially the case on 4BT engines that utilize a Bosch P7100, or P-Pump fuel injection pump. By modifying the p-pump injection pump, you can get extra horsepower/torque very easily.

You can improve 4BT Cummins performance specs easily because they share many of the same internals as 12V 5.9L Cummins engines. 4BT Cummins engines are frequently used in swaps in which a Diesel engine is added to a vehicle like a Jeep Wrangler or a light-duty pickup truck. In these cases, the engines are often modified for greater than stock performance. There are a ton of 4BT Cummins performance upgrades out there like modified injectors, turbochargers, and others. Aftermarket intercoolers are a must-have as these engines don’t come with one from the factory. Many people also upgrade them for greater durability by using ARP head studs.

Fuel Economy

Cummins diesel engines are known to be fuel efficient by most diesel truck enthusiasts. This engine holds that stereo-type to be true. The combination of this engine’s design, turbocharging, and direct fuel injection make the 4BT very fuel efficient. This is a major reason in why this engine is commonly used in Jeep Wranglers or even old classic cars. It can offer mpg in the high-teens or 20s in many applications.

3.9L 4BT Cummins Engine Specs

3.9L 4BT Cummins Engine Specs