Cummins 4BT 101 | BASICS AND PERFORMANCE

4BT BASICS AND PERFORMANCE

THE POPULARITY OF diesel-powered vehicles here in the U.S. has jumped dramatically in recent years. More and more manufacturers are offering new diesel power plants in ½-ton trucks, cars and midsize SUVs. Maybe the reasons for the boost are better highway fuel efficiency and the giant increase in torque offered by a diesel engine, but it’s probably an attempt to meet everincreasing CAFE (Corporate Average Fuel Economy) numbers. Either way, these smaller V-6 and four-cylinder engines will be sticking around. But back in the day, it was Cummins that developed its own small diesel engine market with the 3.9L 4BT.

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4BT History

The 4BT—which stands for “fourcylinder B series turbocharged”— was used mostly in midsize box trucks, agricultural equipment and small industrial vehicles, and is basically a smaller version of the popular 5.9L 12V Cummins found in 1989-98 Dodge trucks. The 4BT shares virtually all of its parts with its big brother, the 6BT (e.g. pistons, connecting rods, injectors and valve-train design).

The 3.9L 4BT Cummins diesel engine has become an extremely popular platform for conversion projects throughout the past couple of years, and for good reason. Sharing virtually every internal and external piece with its big brother, the 5.9L 12V Cummins found in the 1989-98 Dodge Ram pickups, and coming as regular equipment in hundreds of commercial and industrial applications, parts availability, power potential, fuel mileage and the lack of electronics make it an easy go-to engine when it’s time to squeeze a diesel platform into the frame rails of just about anything.

The major internal difference comes from the lack of two cylinders, which means two fewer journals on the crankshaft, a shorter camshaft, two fewer pistons in the injection pump, etc. But even these pieces are the same as the 6BT, just in an inline four-cylinder version. Because of these similarities, the 4BT Cummins has an extremely strong aftermarket, since many 5.9L 12V performance parts can be used in smaller 3.9L engines. This, paired with the somewhat compact size of the 4BT, makes it a great candidate as a transplant engine for just about any vehicle. We’ve seen 4BTs in everything from Jeeps to old-school rat rods. The simplicity of the mechanical injection system also helps make it an easy swap because there’s little to no wiring or electronics required.

The 4BT engine has been used in commercial utility trucks and industrial construction equipment since the late-’80s, and because of its extremely basic functionality, it works well as a transplant engine when space is tight. With the cylinder head off the 4BT engine, someone with 12V Cummins experience should feel right at home. The 4BT is virtually the same, just two pistons shy.

Since the engine was originally developed for industrial applications, big horsepower wasn’t a major concern, and the 239-cid motor most commonly came from the factory at around 105 hp at 2,300 rpm and 265 lb-ft of torque at 1,600 rpm. But these numbers could vary as much as 150 hp depending on the application.

The 4BT engine uses a simple two-valve-percylinder system, one for intake and one for exhaust. While this design became somewhat outdated with the introduction of the fourvalve- per-cylinder design found in the 1998.5- plus 6BT engines, it’s still a sufficient and robust design, especially on the smaller cubic inch, low 130-180-hp applications for which most of the 4BT engines were designed.

The 4BT engine weighs 750- 780 pounds, which is heavier than most of the gas engines it would replace in a conversion project, but much lighter than the sixcylinder 6BT version. The inlinefour also offers a fairly compact size at just 30.6 inches long and 37.7 inches tall, which is useful with space constraints. The engines came with a few different injection pump systems, but the P7100 is, by far, the most popular, since it’s capable of producing larger amounts of fuel and more easily modified by the aftermarket to increase power outputs.

ACD Engines of Salt Lake City is a strong Cummins engine and parts dealer with years of experience in both the 6BT and 4BT platforms. It’s gained a reputation for its 4BT conversion projects and has developed new engine internals to take the average industrial 130-hp four-cylinder diesel to impressive performance heights. Starting with a one-of-a-kind connecting rod and piston design, ACD will soon offer complete Stroker Kits to pump up the power of 4BT platforms. The new H-beam 4340 billet connecting rod (left) was engineered specifically for the 4BT engine. These rods not only help increase engine stroke, they also provide unmatched durability to withstand extreme cylinder pressures from running massive power and torque through these engines. The new H-beam rod (top right) is pictured with a factory 4BT rod (bottom right). An untrained eye may not notice much, but the design and material of the ACD connecting rods is far superior to the standard.

Performance Mods

As previously mentioned, the 4BT can easily be modified to produce higher than stock power levels when outfitted with the P7100 (P-pump). Fueling mods can be taken to the same extremes as with the 5.9L 12V Cummins: 12mm and 13mm pumps with laser-cut delivery valves, high-rev governor springs, full-travel rack plugs and modified injectors can all be used in the 4BT platform. To go along with major fuel upgrades, common cylinder head and turbocharger upgrades are required, but the aftermarket already has most of that covered as well with head studs, better valve springs, larger valves and even performance exhaust manifolds and camshafts built for four-cylinder diesels. While these upgrades can take the 4BT to all-new levels, we have to mention that because of its lack of cylinders and nearly identical operating rpm range, each piston is going to undergo a combustion cycle much sooner than that in a 6BT Cummins, so things like camshaft profiles and pump timing become critical for maximum efficiency at higher horsepower levels.

A close-up of the two connecting rods’ piston ends show where some of the additional piston stroke comes from. Notice the much smaller diameter used to encase the piston’s wrist pin. This new connecting rod design runs exclusively with ACD’s custom-forged pistons using a tool-steel wrist pin. The combination of rod and piston raises the 4BT’s piston stroke from a factory 4.72 inches to a massive 5.430 inches. This alone will increase the engine’s cubic inches from an OEM 239 to just over 275, turning the average 3.9L 4BT into a 4.5L engine.

Knowing that customers interested in a 4BT Stroker Kit would want to make as much horsepower as possible, ACD decided robust forged pistons would be the best option to ensure maximum strength and durability. The combination of the forged piston and tool-steel wrist pin, with special coating to reduce wear and friction, should create a near indestructible product. The piston bowls have also been worked over compared to a stock piston to promote a better swirl effect for a cleaner, more efficient burn in the combustion chamber.

ACD Stroker Kit

Like any engine platform, it’s a well-known fact that more cubic inches generally means more power, and there’s only so much a 239-cid motor can produce, at least safely and efficiently. With this in mind, ACD Engines of Salt Lake City has developed its Stroker Kit to take the 4BT to heretofore unheard of performance heights.

LIKE ANY ENGINE PLATFORM, IT’S A WELL-KNOWN FACT THAT MORE CUBIC INCHES GENERALLY MEANS MORE POWER, AND THERE’S ONLY SO MUCH A 239-CID MOTOR CAN PRODUCE, AT LEAST SAFELY AND EFFICIENTLY.”

Also known locally as “All Cummins Engines,” ACD has been a full-line Cummins dealer for more than 20 years, specializing in midrange and industrial engines. It offers virtually everything Cummins: new or remanufactured engines, new genuine Cummins parts, used engines and even salvage parts. Since it deals in nothing but Cummins, ACD stocks many hard-to-find parts, and if it’s not in stock, the staff knows where to get what you need. Through their years of experience, the staff has become extremely wellversed in the 4BT platform and has the conversion process down to a science, inserting the small Cummins engine into Jeeps, small SUVs, pickups and even a mid- ’50s ambulance.

Sitting side by side on the bench, the stock piston on the left looks quite a bit different from the ACD version. The shorter skirt and much higher wrist pin location were used to assist piston stroke, allowing more displacement and performance potential. More cubic inches means more air and fuel can be drawn into the cylinders to create more power.

In the search for more power, owner Robby Pederson began development of a Stroker Kit that would increase the length of stroke and add some additional cubic inches to the inline-four diesel. In the gas world, Stroker engines are nothing new; the GM small-block 383 Stroker engines have been around for nearly 35 years. The 383 is built using a standard GM 350- cid engine block with a modified 400-cid crankshaft, which changes how far the piston travels.

For the new forged piston design, ACD opted for complete gapless piston ring sets to limit cylinder pressure blow-by and keep the combustion power inside the cylinder where it belongs. This ring design is also durable, but block machining is critical, especially with the use of forged pistons. Where a stock cast piston would only need .005-inch clearance between it and the cylinder wall, a forged piston will swell more under heat and stress, so piston-to-wall clearance needs to be increased to keep the rings from sticking and potentially ruining the piston and engine block.

ACD has plans to install this first monster Stroker 4BT engine into the shop’s H1 Hummer that rests on custom-built axles and 40-inch tires. The shop’s aim is to prove the power potential of the little 4BT and its extreme versatility as the perfect diesel conversion engine for an older vehicle with mild power upgrades (like ACD’s camshaft and injection pump). The goal is to increase a stock 4BT from its underwhelming 130 hp to 200 or even 250 hp to a full-on competition 700-plus-hp engine, like this Stroker should become. It all starts with a clean, bare engine block machined to precise cylinder and crank measurements.

New Rods and Pistons

Because the factory 4BT crankshaft is a robust piece, Pederson didn’t want to do much crankshaft work, so he opted for an all-new piston and connecting rod design to gain the additional stroke he was after. A factory 4BT engine runs a 4.02-inch bore with a 4.72-inch stroke; this is how we come to a 239-ci motor. The new parts from ACD will allow the overall piston bore to expand to 4.402 inches with a much longer 5.430-inch stroke, effectively taking engine output to 333 ci, or 5.46L, almost that of the 5.9L 12V Cummins.

While the 5.9L 6BT Cummins can run into block flex and main cap issues at high power levels, the shorter 4BT won’t be as susceptible to those issues. However, ACD still prefers to use a bottomend Gorilla girdle to tie everything together in the lower part of the engine. ARP main studs are used to ensure proper clamping force is torqued onto the girdle and crankshaft’s main caps.

Knowing that the clientele for such a kit would be after extreme power levels, only the best materials were used to ensure the ACD Stroker Kit would stand up to high boost and high cylinder pressures. Rather than use standard-cast pistons, like the stock units, ACD went with a much stronger forged piston design that offers a different bowl design to improve the air/fuel swirl effect, helping create a more efficient burn in the combustion chamber. The piston design also has a much shorter overall height, and the wrist pin location was moved closer to the deck. These modifications account for most of the additional stroke.

On the cylinder head, upgrades to the ACD 4BT are much the same as those found in performance 12V Cummins builds: high-rev valve springs, titanium keepers, chrome-moly pushrods, etc. For this particular application, ACD will also run fully ported and polished intake and exhaust ports along with larger valves to increase the air volume fed to and expelled from the engine. To help those larger valves perform, ACD spent countless hours developing different camshaft profiles that maximize lift and duration in 4BT engines. Since the injection events are so close together with the inline-four design, the right camshaft profile is critical to how these engines perform. ACD can recommend the correct cam for any build, whether for power or fuel efficiency.

In high-revving and high-horsepower engine applications, the factory press-in freeze plug design is a common failure point. To prevent failure, ACD tapped the cylinder head water ports to accept threaded plugs.

To match the new piston, connecting rods were developed and made from billet 4340, like those being used in all of the high-horsepower diesel engines. The new H-beam rod design is not only stronger than a factory connecting rod, but it also has a much smaller wrist pin journal, which will only work with the ACD piston. While the pistons and rods are the true heart of the Stroker Kit, ACD has also developed a host of 4BT parts to complement them and ensure true peak performance is achieved. Specific camshaft profiles were designed, custom cylinder head work was done and 4BT-specific adjustable injection pump timing gears were installed. The short time between injection events on the four-cylinder engine required a slight engineering change for these parts, and ACD thinks its developed the perfect pieces to turn your run-of-the-mill 105-hp 4BT into a tire-shredding 800-hp monster.

Because this engine will run higher boost pressures, the cylinder head will be machined to use a custom fi re-ringed head gasket kit and ARP head studs. The factory rocker pedestals must be machined for clearance to accommodate the stronger ARP hardware.

The Bosch P7100 injection pump has come a long way since its start in 1994-98 Ram trucks. Originally developed to support the mid 200-hp range, the 4BT platform with just four cylinders moved even less fuel because it only needed to support 130-150 hp in most applications. Using knowledge from the massive 12V performance market, those same techniques and modifications were used in the ACD injection pump. This 13mm pump uses laser-cut delivery valves, max-rack travel plug, stronger hold-downs and a custom cam design specific to the 4BT pump to maximize fuel injection under the quicker injection events to which the four-cylinder engine is subject. This particular pump is capable of moving up to 800ccs of fuel, more than enough to move the big H1 Hummer down the street—doing long third-gear burnouts the whole way.

The fuel injectors for the 4BT engine were also reworked to maximize the amount of fuel that could be effi ciently injected and burned in the cylinders. The dual-feed injectors and customhoned nozzles should be more than enough to support ACD’s 800-hp goal. The custom highfl ow injection lines will also be used to eliminate any restrictions between the injection pump delivery valves and the injectors.

ACD Engines understands that the complete Stroker Kit might be more than most 4BT project vehicles need, so it has an array of 4BT-specific products that can do everything from increasing power to improving fuel mileage and engine efficiency. It also carries a full line of custom brackets and conversion pieces to make your conversion or transplant project go a little easier.

ACD will use the OEM Cummins valve covers on this high-horsepower build, which offers dual port ventilation. While the gapless piston rings should cut down on most of the engine’s blow-by, the high-flow breathers in these valve covers will be much more efficient than the individual factory cylinder covers found on most 4BT and 6BT engines.

Since the cylinder head intake and exhaust sides were ported and polished to maximize airflow through the head, it’s only natural to upgrade the exhaust manifold. While there are different OEM-style manifolds for the 4BT that suit different installation needs, they don’t necessarily fl ow what a high-horsepower build like this one would need. ACD turned to Steed Speed for help. It offers these customfabricated manifolds with both T3 and T4 turbo flanges along with center- and top-mount exit locations. These different turbo mount locations should be more than enough to fit a 4BT into the chassis of just about anything.

[divider]SOURCE[/divider]

• ACD Engines
877.506.8667
Acdengines.com

FREQUENTLY ASKED QUESTIONS

Are there more modern diesel engine options that might be better choices than the 3.9L Cummins?

Considering Modern Diesel Engine Alternatives to the 3.9L Cummins

Absolutely, there are various modern diesel engine options that might be superior choices compared to the 3.9L Cummins.

Advantages of Modern Diesel Engines

Modern diesel engines often come with advancements that offer:

Improved fuel efficiency
Lower emissions
Enhanced performance

Popular Alternatives

Duramax 3.0L
- Fuel Economy: This engine is designed to deliver excellent fuel economy.
- Power: Offers impressive power and torque, making it suitable for heavy-duty applications.
Power Stroke 3.2L
- Durability: Known for its robust design, which ensures longevity.
- Technology: Equipped with modern technology for better control and efficiency.
EcoDiesel 3.0L
- Emissions: Engineered to meet stringent emission standards.
- Noise Levels: Quieter operation compared to older diesel engines.

Why Choose Modern Alternatives?

Reliability: Modern engines are often more reliable than older models like the 3.9L Cummins.
Performance: These engines generally provide better performance in terms of speed and towing capacity.
Cost-Efficiency: Although initially more expensive, the long-term savings in fuel and maintenance can be substantial.

In summary, while the 3.9L Cummins is reliable, newer diesel engines like the Duramax 3.0L, Power Stroke 3.2L, and EcoDiesel 3.0L come with significant benefits that make them worth considering.

What are some drawbacks of the 3.9L Cummins engine?

Drawbacks of the 3.9L Cummins Engine

The 3.9L Cummins engine, while rugged and reliable, comes with several drawbacks that potential users should consider.

Antiquated DesignFirstly, it’s important to note that this isn’t a modern diesel engine. Its design is somewhat outdated, resulting in a lack of the refinement found in newer models.
Noise and VibrationThis older design means that the engine tends to be quite noisy. The clattering and vibration may be off-putting for some, especially if you value a quieter ride.
Limited Tuning OptionsUnlike modern engines, you can’t simply plug in a programmer and achieve significant horsepower gains. Modifying the power output of the 3.9L Cummins requires considerable effort and investment. It’s not a simple plug-and-play situation.
Investment Required for Performance BoostsYes, you can boost the power, but it involves significant work and financial resources. Achieving performance levels that are worth bragging about means you need to invest in various aftermarket parts and labor.

In summary, the 3.9L Cummins provides durability but falls short in areas of refinement, noise levels, and ease of tuning. Assess your priorities and resources before committing to this engine.

Why might fuel economy not be a sufficient reason to swap to a 3.9L Cummins engine?

Why Fuel Economy Alone May Not Justify Swapping to a 3.9L Cummins Engine

Swapping to a 3.9L Cummins engine might seem enticing for those looking to improve fuel economy, but this consideration alone may not be sufficient to warrant the conversion. Here’s why:

Weight and Handling Impact

The 3.9L Cummins engine is quite heavy, weighing about a third of a Jeep Wrangler. This added mass can negatively affect the vehicle’s handling and overall performance. Moreover, the increased weight places additional stress on the suspension and axles, potentially leading to more wear and tear, especially in smaller vehicles like Jeeps.

Challenges with Additional Components

Both the 4BT and 4BTA variants are non-intercooled, turbo-diesel engines. While this eases installation by eliminating the need for intercooler ducting, enhancing performance will likely require you to add an intercooler. Fitting this component under the hood can be challenging and may require substantial modifications.

Fuel Savings May Not Balance Costs

The potential fuel savings vary significantly based on the engine you are replacing. For instance, if your current vehicle averages around 15 miles per gallon, you might not see substantial savings since post-conversion fuel efficiency tends to range between 17 and 21 mpg. This marginal improvement may not justify the costs associated with the engine swap, making it harder to recoup your investment through fuel savings alone.

Vehicle Type Considerations

For heavier trucks and SUVs, the weight added by the 3.9L Cummins engine might not be as critical an issue compared to smaller 4x4s. Weight becomes a relative challenge in heavily modified off-road vehicles, where handling and stress distribution are more crucial.

Conclusion

While improving fuel economy is certainly appealing, it shouldn’t be your sole reason for swapping to a 3.9L Cummins engine. The added weight, potential handling issues, the need for additional components, and modest fuel savings make it essential to weigh all factors before committing to such a conversion. Consider looking at the complete picture, including how the weight and stress impact your specific vehicle type and your particular use case, before making this significant modification.

What are the typical fuel economy figures for vehicles with a 3.9L Cummins engine swap?

Typical Fuel Economy Figures for Vehicles with a 3.9L Cummins Engine Swap

When swapping a 3.9L Cummins engine into a vehicle, fuel economy typically falls within a certain range. Real-world data suggests that you can expect between 17 and 21 miles per gallon (mpg).

However, these figures are influenced by various factors, including:

Vehicle weight:Heavier vehicles tend to consume more fuel.
Driving habits:Aggressive driving can decrease fuel economy.
Load and usage:Towing heavy loads or frequent stop-and-go driving can also affect mpg.

In essence, while the 3.9L Cummins engine offers a broad range of fuel efficiency, specific results will vary based on how and where you drive.

What types of vehicles are better suited for the 3.9L Cummins engine swap?

Vehicle Suitability

When it comes to engine swaps, the 3.9L Cummins is definitely worth bringing to the table. If you have a full-size application, such as trucks or larger SUVs, the 4BT isn’t a bad option. It’s particularly appealing if you’re looking to build a reliable overland-type rig that can handle long-distance travel and rough terrain.

For more compact and nimble vehicles, like the Jeep Wrangler, the 3.9L Cummins might not be the best option. The weight and size of the engine could affect the vehicle’s handling and performance. There are better-suited engine options for these kinds of vehicles, which are designed to maintain their agility and off-road capabilities.

In summary, the 3.9L 4BT Cummins diesel engine offers a versatile and robust option for a variety of vehicle conversions but shines brightest in full-size vehicles where its power and simplicity can be fully utilized. Whether you’re working on an overland rig or a custom build, understanding the suitable applications for this engine can help you make the best choice for your project.

Can the 3.9L Cummins engine’s power be increased, and what does it entail?

The 4BT can easily be modified to produce higher than stock power levels when outfitted with the P7100 (P-pump). Fueling mods can be taken to the same extremes as with the 5.9L 12V Cummins: 12mm and 13mm pumps with laser-cut delivery valves, high-rev governor springs, full-travel rack plugs, and modified injectors can all be used in the 4BT platform. To go along with major fuel upgrades, common cylinder head and turbocharger upgrades are required, but the aftermarket already has most of that covered as well with head studs, better valve springs, larger valves, and even performance exhaust manifolds and camshafts built for four-cylinder diesels.

While these upgrades can take the 4BT to all-new levels, we have to mention that because of its lack of cylinders and nearly identical operating rpm range, each piston is going to undergo a combustion cycle much sooner than that in a 6BT Cummins, so things like camshaft profiles and pump timing become critical for maximum efficiency at higher horsepower levels.

However, it’s important to note that the 4BT is not a modern diesel. In fact, it’s a bit antiquated and unrefined. For some, the rattle, shake, and noise of this diesel will be too much. These characteristics can be a significant drawback if you’re looking for a smoother, quieter ride.

Additionally, you can’t simply hook a programmer to a 4BT and voila—you have 500hp. Yes, you can turn up the power, but it’s going to take real work and a serious investment of funds to get the numbers into the bragging realm. This means that while the 4BT has a lot of potential, prospective modifiers should be prepared for the commitment in both time and money.

By understanding these limitations and the extent of modifications necessary, you can better assess whether the 4BT is the right platform for your performance goals.

How does the weight of the 3.9L Cummins engine affect vehicle handling and suspension?

The 4BT engine weighs 750-780 pounds, which is heavier than most of the gas engines it would replace in a conversion project, but much lighter than the six-cylinder 6BT version. The inline-four also offers a fairly compact size at just 30.6 inches long and 37.7 inches tall, which is useful with space constraints.

However, this added weight can put more strain on the vehicle’s suspension and axles. For full-size trucks or SUVs, the weight won’t be as much of an issue due to their robust build. Weight is often relative when it comes to heavily modified 4x4s, meaning the impact can vary significantly based on the level of modification.

Key Takeaways:

Weight Impact:The 4BT engine’s weight is heavier than most gas engines but lighter than its six-cylinder counterpart.
Size Benefits:Its compact dimensions help mitigate space constraints in conversion projects.
Suspension and Axle Strain:Added weight increases strain on these components, particularly in less robust vehicles.
Vehicle Type Consideration:Full-size trucks and SUVs are less affected by the added weight, whereas heavily modified 4x4s might experience varied impacts.

This nuanced understanding helps in making informed decisions when considering a 4BT engine conversion, ensuring vehicle handling and suspension are adequately addressed.

How do the pre-1998 and post-1998 3.9L Cummins engines differ in terms of valves and power output?

“The 4BT engine uses a simple two-valve-per-cylinder system, one for intake and one for exhaust. While this design became somewhat outdated with the introduction of the four-valve-per-cylinder design found in the 1998.5-plus 6BT engines, it’s still a sufficient and robust design, especially on the smaller cubic inch, low 130-180-hp applications for which most of the 4BT engines were designed.

Pre-1998 vs. Post-1998 3.9L Cummins Engines

Pre-1998 4BT engines feature an eight-valve configuration, delivering power ratings of 105hp and 265 lb-ft of torque. However, post-1998 units, known as the 4BTA, transitioned to a 16-valve setup. This valvetrain adjustment resulted in a significant base horsepower increase to 170hp and a more impressive 420 lb-ft of torque. Power figures can vary depending on the application, but the enhancements made in the post-1998 models are evident.

In summary, while the 4BT’s two-valve-per-cylinder system remains effective for its intended applications, the advancements seen in the 4BTA models demonstrate the benefits of increased valve counts and improved power output. This evolution highlights the ongoing improvements in engine design to meet higher performance demands.”

What are some common applications for the 3.9L Cummins engine?

The 4BT—which stands for “four-cylinder B series turbocharged”—was used mostly in midsize box trucks, agricultural equipment, and small industrial vehicles, and is basically a smaller version of the popular 5.9L 12V Cummins found in 1989-98 Dodge trucks. The 4BT shares virtually all of its parts with its big brother, the 6BT (e.g., pistons, connecting rods, injectors, and valve-train design).

Hitting the market in 1983, the first 3.9L Cummins (known as the 4BT) has been used in everything from delivery trucks to wood chippers. This means they can be found anywhere, and for really cheap. The 3.9L 4BT Cumminsdiesel engine has become an extremely popular platform for conversion projects throughout the past couple of years, and for good reason. Sharing virtually every internal and external piece with its big brother, the 5.9L 12V Cumminsfound in the 1989-98 Dodge Ram pickups, and coming as regular equipment in hundreds of commercial and industrial applications, parts availability, power potential, fuel mileage, and the lack of electronics make it an easy go-to engine when it’s time to squeeze a diesel platform into the frame rails of just about anything.

The 4BT engine has been used in commercial utility trucks and industrial construction equipment since the late-’80s, and because of its extremely basic functionality, it works well as a transplant engine when space is tight.

Why is the 3.9L Cummins engine popular for engine swaps?

Why the 3.9L Cummins is a Top Choice for Swaps

Technical Specifications

Horsepower: 105hp
Torque: 265 lb-ft
Dimensions: 30.6 in long, 24.6 in wide, 37.7 in high
Weight: Nearly 800 pounds

These figures show that despite its relatively compact size, the 3.9L Cummins packs a punch, making it perfect for a variety of conversion projects.

Historical Context and Versatility

First hitting the market in 1983, the 3.9L Cummins, also known as the 4BT, has been utilized in everything from delivery trucks to wood chippers. This widespread use means the engines are not only easy to find but also affordable. Their robust design and mass availability make them a practical choice for enthusiasts looking for reliability without breaking the bank.

Simplicity and Ease of Conversion

One of the standout features of the 3.9L Cummins is its minimal reliance on electronics. This simplicity significantly eases the conversion process, allowing for a smoother integration into various projects. Whether you’re dealing with an older vehicle or a custom build, fewer electronics mean fewer complications.

Transmission Options

The engine’s compatibility with a slew of manual and automatic transmission options adds another layer of versatility. It allows for a wide range of applications, catering to different needs and preferences.

Durability and Reliability

Sharing much of its DNA with the revered 5.9L 12-valve Cummins, the 3.9L offers a similar promise of durability and reliability. This connection gives diesel enthusiasts confidence that the engine can withstand the test of time and usage.

In conclusion, while there might be other diesel options out there, few can match the 3.9L Cummins in terms of cost-effectiveness, ease of conversion, and overall reliability. It’s no wonder this engine remains a favorite among those looking to undertake conversion projects.

How much power and torque does the 3.9L Cummins engine produce?

The engine was originally developed for industrial applications, big horsepower wasn’t a major concern, and the 239-cid motor most commonly came from the factory at around 105 hp at 2,300 rpm and 265 lb-ft of torque at 1,600 rpm. But these numbers could vary as much as 150 hp depending on the application.

One diesel engine in particular that pops up more than most is the 3.9L Cummins. The 3.9L (4BT) Cummins inline-four diesel engine creates 105 hp and 265 lb-ft of torque from its relatively small size of 30.6 inches long, 24.6 inches wide, and 37.7 inches high.

Pre-1998 Models: The pre-1998 4BT engines have eight valves and received power ratings of 105 hp and 265 lb-ft of torque.
Post-1998 Models: Post-1998 units, known as the 4BTA, switched to a 16-valve configuration. With this valvetrain adjustment, the base horsepower bumped up to 170 hp and torque to an impressive 420 lb-ft.

Depending on the application, the power figures can vary, making this engine versatile for various uses.

What are the pros and cons of the 3.9L Cummins (4BT) diesel engine?

The 3.9L 4BT Cummins diesel engine has become an extremely popular platform for conversion projects throughout the past couple of years, and for good reason. Sharing virtually every internal and external piece with its big brother, the 5.9L 12V Cummins found in the 1989-98 Dodge Ram pickups, and coming as regular equipment in hundreds of commercial and industrial applications, parts availability, power potential, fuel mileage, and the lack of electronics make it an easy go-to engine when it’s time to squeeze a diesel platform into the frame rails of just about anything. Because of these similarities, the 4BT Cummins has an extremely strong aftermarket, since many 5.9L 12V performance parts can be used in smaller 3.9L engines. This, paired with the somewhat compact size of the 4BT, makes it a great candidate as a transplant engine for just about any vehicle.

Pros of the 3.9L Cummins (4BT) Diesel Engine

Compact Size and Power: Despite its relatively small dimensions (30.6 in long, 24.6 in wide, and 37.7 in high), the 3.9L Cummins generates 105hp and 265 lb-ft of torque.
Versatility and Availability: This engine has been used in a variety of applications, from delivery trucks to wood chippers, making it readily available and often inexpensive.
Simplicity: With minimal electronics required, the engine simplifies the conversion process.
Compatibility: Sharing many components with the 5.9L Cummins ensures good parts availability and reliability.
Mechanical Injection Pump: The P7100 mechanical injection pump is preferred for its reliability and ease of modification.
Fuel Economy: Offers moderate fuel savings, with real-world numbers ranging between 17-21 mpg, depending on the application.

Cons of the 3.9L Cummins (4BT) Diesel Engine

Weight: Weighing nearly 800 pounds, the engine can negatively affect handling and put additional strain on suspension and axles, especially in smaller vehicles like the Jeep Wrangler.
Non-Intercooled: Both the 4BT and 4BTA versions are non-intercooled, which could be a limitation for those seeking higher power.
Antiquated Design: The older technology results in more noise, vibration, and a lack of modern refinements.
Power Tuning Limitations: Increasing power requires significant investment and effort, unlike modern engines that can be easily tuned.

Overall, the 3.9L Cummins diesel engine stands out for its mass availability, simplicity, and versatility. However, it is important to weigh these advantages against its drawbacks, particularly the added weight and lack of modern refinements. If you’re considering an engine swap, the 3.9L Cummins offers a robust and reliable option, especially for full-size applications. For smaller, more nimble vehicles, you may want to explore other alternatives.