4BT Cummins: Everything You Want to Know | Specs and More

In the off-road community engine swaps can be a touchy subject. Most of the time torque is what you’re looking for. Because of that, Chevrolet LS engines are pretty common, especially the truck version of that engine. But, diesel engines are becoming increasingly popular, specifically the 4BT Cummins.

Before I tell you what makes the 4BT so awesome for off-roading, I must first inform you of the basics of the engine. You can find even more 4BT information on Wikipedia.

4BT Cummins: Engine Basics

If you’re at all familiar with the 6BT Cummins, then you’re in luck. Other than the obvious fact of one being a 6-cylinder and one being a 4-cylinder, they are extremely similar. The pistons, injectors, connecting rods, and valvetrain design are straight off of the 12v Cummins.

  • Displacement: 3.9L – 292ci
  • Cylinder Head Material: Cast Iron
  • Engine Block Material: Cast Iron
  • Compression Ratio: 17.5:1
  • Valvetrain: OHV – 2 Valves per Cylinder
  • Horsepower: 105hp
  • Torque: 265 lb-ft

One thing that really sticks out from this whole chart is the weight. The 4BT Cummins weighs about 750 lbs, which can drastically change the handling of your vehicle if you plan on swapping a 4BT in.

4BT Cummins: Real World Applications

Diesel engines are really common in heavy duty applications. Things like semi-trucks, tractors, and large generators use diesel engines. But what about things that are sort of heavy duty, but sort of not? Something like a bread truck falls into that category, and that’s where the 4BT comes into play.

The 4BT was extremely common in step trucks, as well as other heavy-ish duty applications. Today in 2016 the 4BT has been replaced with much more efficient diesel engines, but the 4BT is still being used today.

4BT Cummins: Performance Data

The 4BT is by no means a performance engine. As I said above it was used in applications such as bread trucks. The 4BT produced 105 horsepower @ 2,300 RPM and 265 lb-ft @ 1,600 RPM. This was perfectly fine for the applications that it was used in.

But, what can the 4BT really do? After all, it’s basically a 4-cylinder version of the 12 valve Cummins which is known to respond excellently to modifications.

4BT Cummins: Tuning Potential

I will tell you right now, I am by no means an expert in diesel engines. But, after poking around some diesel forums it seems the most you can really make reliably with a 4BT is about 300whp.  The same common modifications that you’d find on a 12 valve apply to the 4BT. Things like a turbo upgrade, injector upgrade, and fuel pump work will keep the 4BT reliable whilst making more power than stock.

Although it doesn’t make a whole lot of horsepower with those upgrades, it does make a ton of torque. With those common upgrades, the 4BT can make as much as 700 lb-ft.

4BT Cummins: Why Swap?

So from everything, I’ve told you so far, why would you want to swap a 4BT into your vehicle? If you’re able to fit a 6BT 12 valve into your vehicle, then that is probably the way better option. It’ll make more power, last just as long, and might be cheaper to buy.

RELATED: 6BT Cummins: Everything You Want to Know

The real reason you might want to swap a 4BT is for fuel mileage, and size constants. A 4BT barely fits into an XJ Cherokee with a 6″+ lift, so a 6BT is definitely out of the question for many Jeep owners. If fuel mileage is your legitimate reason for swapping, then the 1.9 TDI from VW is a far better option.


So what have we learned so far? The 4BT came in heavy duty applications such as bread trucks, it’s nearly identical to the 12 valve, it responds to modifications just like a 12 valve, and it’s incredibly reliable. Many 4BT engines have gone way past 300,000 miles.

Jeep people love the 4BT because its pretty much the best diesel that can actually fit inside of a Jeep other than the much less common 1.9 TDI swap. Let me know what you think of the 4BT in the comments below!

About Bryce Cleveland 267 Articles
Bryce founded Dust Runners Automotive Journal in 2014 as a way to write about the cars he found interesting. When he's not writing for Dust Runners he's writing for Power Automedia as a freelancer. He currently drives a 2015 Fiesta ST and absolutely loves it.


  1. What I’m curious about is the horsepower and torque ratings for the Cummins 4BT diesel. 105hp and 265lbs-ft torque doesn’t seem like much for an engine of 3.9 litres or for most apps.

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