Cummins B Series engine. The Cummins B Series is a family of diesel engines produced by American manufacturer Cummins.  In production since 1984, the B series engine family is intended for multiple applications on and off-highway, light-duty, and medium-duty.  In the automotive industry, it is best known for its use in school buses, public service buses (most commonly the Dennis Dart and the Alexander Dennis Enviro400) in the United Kingdom, and Dodge/Ram pickup trucks.

Since its introduction, three generations of the B series engine have been produced, offered in both inline-four and inline-six configurations in multiple displacements.

General engine features
The B-series features engine bores machined directly into the block (rather than the wet liners used on earlier Cummins engines). It is also set apart by the use of a shallow one-piece head, requiring closer tolerances than in other Cummins products. Unlike earlier diesel engines the B-series Cummins used direct injection and did not need glow plugs for cold starting.  The engine was first manufactured in Rocky Mount, North Carolina, and other plants were later added in Mexico, Brazil, Turkey, and Darlington, UK.

It uses a gear-drive camshaft for extra reliability. Also specified is a deep-skirt engine block and extra-strong connecting rods. A Holset turbocharger is used. The original B Series was updated with 24 valves and an electronic engine management system to become the ISB in 1998.

Engine specifications

B engine

3.9 L
The 3.9-liter 4B/4BT/4BTA Cummins is categorized under the B Engine family alongside the 5.9-liter 6B/6BT/6BTA Cummins diesel engines. The 3.9 is an inline four-cylinder, either naturally aspirated (4B) or turbodiesel (4BT/4BTA), which was popular for many step van applications including bread vans and other commercial vehicles. Additionally it has seen broad usage in agricultural equipment. It has also gained popularity as an engine swap into smaller trucks and SUVs.

4B 
The lowest powered, naturally aspirated 3.9-liter Cummins, the 4B, produces . This variant is most commonly found in equipment such as generators and wood chippers.

4BT 
The 4BT is one of two turbocharged variants of the 3.9L B-Series engine. It has two valves per cylinder for a total of eight. The most common output of this variant is 105 horsepower.

4BTA 
The 4BTA is turbocharged, and aftercooled with four valves per cylinder for a total of sixteen. The most common output of this variant is 170 horsepower.

5.9 L

The 5.9 L Cummins, also known as the "12-Valve" Cummins was the first member of the Cummins B-Series to be used in a light truck vehicle. The 6BT used Bosch fuel systems, injector, and VE rotary pump and P7100 inline injection pumps. Some early 6BTs were supplied with CAV rotary pumps instead, before the Bosch system became the sole standard. This engine started life in 1984 designed as an agricultural engine, for use in Case agricultural equipment.
After 1989, the 6BT engine was used in light duty, medium duty and select heavy duty trucks and buses. The 6BT engine has recently become very popular for use in repowering various vehicles.

6B 
The 6B is the naturally aspirated version of the 6BT with the power output of between 150 and 173 hp and with the compression ratio of 19:1. There were no OEM automotive applications for 6B engines.

6BT 
Appearing in the 1989–1998 Dodge Ram pickup truck, it became a popular alternative to the large gasoline V8 engines normally used in full-size pickup trucks, since it produced torque at low engine RPM, and achieved significantly better fuel mileage. Due to the direct fuel injection, the 6BT has no glowplugs.

6BTA     
The 6BTA is Turbocharged, and aftercooled, with a air to water after cooler mounted on the intake.  Has a compression ratio of 16.5:1.

ISB engine

4.5 L ISB

The 4.5 L ISB is essentially a four-cylinder, two-thirds version of the 6.7 L ISB rated at , used in the New Routemaster, a series hybrid diesel-electric doubledecker bus in London.

5.9 L ISB 

The  ISB (Interact System B) is one of the largest straight-six engines used for light truck vehicles and school buses, and the improved high output 600 version was on the Ward's 10 Best Engines list for 2004.

One unusual feature of the ISB is that it is a multi-valve pushrod engine design, with four valves per cylinder (popularly referred to as the "24-Valve" Cummins). The engine displaces , with a  cylinder bore and piston stroke. A turbocharger is used to increase the output in the high-compression (17.2:1 in recent versions) diesel. It is an all-iron engine with forged steel connecting rods, an assembled camshaft, and a cast aluminum intake manifold. The engine is produced in Columbus, Indiana.

The ISB uses electronically controlled Bosch fuel systems, unlike the 6BT systems which were mechanical. Early ISB engines utilize Bosch injectors and a Bosch VP44 high pressure pump. Later ISB designs have common rail fuel injection, Bosch injectors, and a Bosch CP3 high pressure pump.

Dodge Ram ISB
Midway through model year 1998, the Dodge Ram switched from the 6BT to the ISB to meet updated emissions requirements. Like other ISB's, these engines started out using the Bosch VP44 rotary injection pump. The VP44 setup meant that timing and fuel could be precisely controlled, which led to cleaner emissions. However, VP44 failure rates were higher than the older P7100 injection pump. The compression ratio in these engines was 17.2:1. The 1998–2000 ISB was rated at  and  when equipped with the 47RE automatic transmission. The 1998–2000 ISB was rated at  and  when equipped with a manual transmission. For the 2001–2002 years, a standard output and a high output ISB Cummins engine were offered. The standard output, which was the same as the previous engines was rated to  and  when equipped with either a manual transmission or automatic. The high output ISB was rated at  and , with only a NV5600 six-speed manual transmission available. The high output engine was different in a few ways from the standard output engine; it had higher compression (17.3:1), powdered metal valve seat inserts, a larger flywheel, the Bosch fuel system was reworked to allow higher fuel flows, and fuel-injection timing was altered.

Dodge Ram ISB CR
For the 2003 model year, the Cummins was introduced with Bosch high pressure common rail fuel injection, again increasing power output. On automatic equipped vehicles, the 47RE was upgraded internally to increase durability and torque capacity, now known as the 48RE. The 2003 rating for the Dodge truck was released at  and . Midway through the 2004 model year, the Cummins 600 was introduced, producing  at 2,900 rpm and  at 1,600 rpm. This engine was noticeably quieter than the previous engines.

6.7 ISB

The 6.7 L ISB is the latest version of the B Series. It is currently the largest straight-six engine produced for a light duty truck or school bus. It produces  and  in the 2007.5 and newer Dodge 2500/3500 pickup trucks with the Chrysler-built six-speed 68RFE automatic transmission built at the Kokomo Transmission plant in Kokomo, Indiana. Engine torque is slightly reduced with the Mercedes G56 6-speed manual transmission at  and . The 2007 and newer 3500 Cab & Chassis trucks only get the  and  version of the B6.7, whether it has the Aisin AS68RC or the Mercedes G56 6-speed manual transmission. As for the 2008 4500/5500 medium duty Chassis Cabs or the Sterling Bullet Trucks, they receive the  and  version of the B6.7, whether it has the Aisin AS68RC or the Mercedes G56 6-speed manual transmission. Late model 2011 Ram trucks produce  and , with the exhaust brake rating boosted from  to .

For 2019 this engine has been updated to produce 400 hp and 1000 ft-lb torque.

It is also used in the Blue Bird Vision, Thomas Saf-T-Liner C2, and IC CE school buses and BMC Procity city buses

Changes over the 5.9 L ISB
There are many changes over the previous 5.9 L ISB for the Dodge truck, the most obvious being the larger displacement. The 6.7 ISB had an increase of cylinder bore and piston stroke to , respectively, thereby giving a displacement of .

With the 6.7 L ISB came the introduction of the Variable Geometry Turbocharger (VGT). The VG Turbocharger was introduced to reduce turbo lag by adjusting the vanes by sliding a steel ring in the exhaust housing dependent on engine RPM creating more or less pressure inside the exhaust housing and controlling the speed of the turbocharger. It also works as an integrated exhaust brake system and is all controlled by an electronic actuator on the turbocharger. This VGT system has been an extremely common issue with the 6.7 L ISB and is typically diagnosed by the loss of the trucks exhaust brake.

QSB engine

5.9 QSB 
The 5.9 L QSB (Quantum System B) is an off-road, heavy duty version of the ISB. Typically used in marine, agricultural, and construction applications, these engines share many of the same parts as the ISB and utilize the same Bosch fuel system.

Fuel system

Mechanical injection with mechanical timing 
In the earlier models of the Cummins B-Series Engine, it was almost entirely mechanical including its fuel system. The fuel pump used in these engines was the Bosch P7100 injection pump, this pump is driven off the camshaft gear and drives its own internal camshaft to inject fuel to the individual injectors. This pump itself was one of the most popular options for fueling for the B-Series Engines because of this simplistic design and how reliable it was. The P7100 injection pump also allows for large amounts of fuel to be delivered into the system with simple tweaking to the system to allow for larger injection events.

Mechanical injection with electronic timing 
In the later models of B-Series Engine, the fuel system was switched from mechanical injection and timing to mechanical injection with electronic timing. This was all thanks to Bosch's new VP44 radial distributor injection pump. The VP44 injection pump is driven at half the camshaft speed and produces an injection pressure of up to .

Mechanical injection with electronic timing and common rail pressurization 
The most recent method of fuel injection used in Cummins B Series engines is electronically controlled common-rail injection. It has been used in Cummins B Series engines and the B-Series based NEF engine since 2003.

References

Chrysler engines
Cummins diesel engines
Diesel engines by model
Straight-six engines