Which Cummins 4BT Diesel Engine Do I Have?

• November 9, 2021
• Story By
  Mike McGlothlin

Perhaps no engine did more to kick off the diesel swap craze than the 4BT Cummins. It was built for the construction, agriculture, marine, power generation, forestry, freight and transportation industries, so it stands to reason why they’re so plentiful—but also why so many different variations of the engine exist. It’s enough to make newbies feel like they’re venturing down a rabbit hole when they first begin to learn about the legendary 3.9L. Seriously, you could find the 4BT in bread vans, gen-sets, boats, old utility tractors, backhoes, wheel loaders, skid-steers, crawlers, swathers and even forklifts, and each engine varied from application to application.

With so many different 4BT’s out there in the wild, it pays to know what you’re looking at before you commit to buying that junkyard, eBay or Marketplace engine. Below, we’ll show you how to identify which 4BT you’re looking at, where to find the all-important CPL number and what the most common CPL numbers mean. Automotive, industrial or marine, the following information could help you narrow down your 4BT search and keep your swap project as straightforward as possible.

Types Of 4BT’s

It may sound like an old record for those in the know, but it is very important that you know exactly what each Cummins acronym system means for this engine. In total, there were four different platforms produced over the years. As basic as basic gets, the “4” represents the cylinder count and the “B” stands for the series of engine (i.e. Cummins B series). The 4B models were non-turbo, the 4BT was turbocharged (T for turbo), the 4BTA was turbocharged (T) and after-cooled (A), and the 4BTAA was turbocharged with an air-to-air intercooler (AA).

What Does CPL Mean?

When you spend any time around the 4BT Cummins you quickly learn how important the engine’s CPL number is. CPL stands for control parts list and it relates to the specific components the engine was assembled with (i.e. emission controls, injectors, injection pump, turbocharger, etc.). Intentionally offering endless configuration possibilities, Cummins could make the 4BT applicable for a wide range of vehicles and equipment—and this is precisely why knowing your engine’s CPL is so important. The 4BT’s CPL is located on the engine data tag. In cases where the data tag is missing, you’ll have to refer to the engine’s serial number for your part ordering needs. The serial number can be found at the back of the block, just below the cylinder head.

Converting An Industrial 4BT For Road Use

Despite the dozens of CPL numbers that exist for the 4BT engine, there are four primary automotive versions: CPL 1839, 2001, 2195 and 2304. Keep in mind that, while the latter engines are often kept in on-road applications, many other versions of the 4BT can be converted (and have been) for road-use. A lot of readying a 4BT for an automotive application exists in changing the pump’s governor to allow for a broader rpm range rather than a set rpm. Another common item that requires addressing is switching from the industrial oil pan to the automotive version for proper clearance within the vehicle.

Common CPL Numbers

To give you an idea as to the different power ratings on some 4BT’s with common CPL numbers, we’ll take a look at CPL 767, 857, 858 and 986. CPL 767 and 858 are standard 4BT models with Bosch VE rotary injection pumps, rated for 105 hp at 2,500 rpm and 265 lb-ft of torque at 1,700 rpm. CPL 857 and 986 were VE-pumped as well, but were intercooled (CPL 857 was a 4BTA and CPL 986 was a 4BTAA) and rated at 120 hp at 2,500 rpm and 300 lb-ft at 1,700 rpm. As a wildcard, we’ll throw in the CPL 1963, a 4BT that packed an inline injection pump but not the Bosch P7100. Rather, it ran a P3000 and is reported to have been rated at 130 hp.

P-pumped 4BT’s Are Rarer Than You Think

Judging by what you may have seen in 4BT swaps, the Bosch P7100 inline injection pump (i.e. P-pump), the pump with the most performance potential, might seem commonplace. On the contrary, factory P-pumped versions of the 4BT are rare. CPL 1839 is one of those rare engines. Intended for an automotive application, this particular 4BTAA features a Bosch P7100, an air-to-air intercooler and was rated for 130 hp and 327 lb-ft when it left the assembly line.

Factory Water-to-Air Intercooling

The 4BTA’s came with water-to-air intercooler built into the intake, such as this one (CPL 857), technically an on-road 4BTA rated for 120 hp at 2,500 rpm and 300 lb-ft at 1,700 rpm from the factory. The water-to-air intercooler operates at the same temperature as the engine coolant, perfect for compact packaging and low-speed applications. As you can see, this CPL also called for the Bosch VE rotary injection pump.

Don’t Turbocharge The 4B

The only notably undesirable 4BT swap candidate is the non-turbo 4B. This engine is typically a no-no because not only is it naturally aspirated, but its compression ratio is high and its power rating is generally low (think 80 hp). Outfitting a naturally aspirated 4B with a turbocharger is asking for head gasket trouble, not to mention that adding boost on top of high compression is much harder on engine internals.

Still More CPL Numbers

With the 4BT Cummins catering to so many different end-user’s needs, it stands to reason why a CPL was included for each engine. Different emissions, power levels and working rpm all played into each 4BT. The on-road versions are notably different than the off-road, emissions-free 4BT’s, with components such as the camshaft, injection pump (timing, CC’s of fuel, hp rating), injectors (high psi and low psi, 7mm and 9mm, nozzle hole size and count), turbos and intercoolers (air-to-air vs. water-to-air) many times being different. And with the 4BT being available in everything from a gen-set to a bread van to a boat, it’s no wonder there were so many different options associated with them. As you’ll find in the extensive list of CPL’s below, most were 4BT versions (turbocharged only, no intercooler).