A farm tractor engine became the diesel heart of Dodge pickups
Introduced in 1984 as an engine for Case farm equipment, the Cummins B Series went on to power bread vans, British buses, almost every new American school bus and Dodge Ram pickups, where its pulling power at low revs made it a popular alternative to big gasoline V8s.
Cummins broke from its earlier engines by machining the cylinder bores straight into the block instead of fitting wet liners, and by using a shallow one-piece head that demanded tighter tolerances. Direct fuel injection meant it needed no glow plugs to start in the cold. A gear-driven camshaft, deep-skirt block, extra-strong connecting rods and a Holset turbocharger were chosen for durability, and the first engines came from Rocky Mount, North Carolina.
The range spans inline fours and sixes. The 3.9-litre four served in step vans and farm machinery and became a popular engine swap, with outputs from 53 hp in the naturally aspirated 4B, found in generators and wood chippers, to 170 hp in the 16-valve 4BTA. The 5.9-litre six, nicknamed the 12-Valve, became the first B Series engine in a light truck, arriving in the 1989–1998 Dodge Ram and winning fans with its low-rev torque and far better fuel mileage.
In 1998 the design gained 24 valves and electronic engine management to become the ISB, and midway through that model year Dodge switched over to meet tighter emissions rules. Its Bosch VP44 pump controlled timing and fuel precisely but failed more often than the older mechanical pump. A high-output version, the 600, made Ward's 10 Best Engines list for 2004.
The 6.7-litre ISB, offered from 2007 to 2018, was the largest straight-six built for a light truck or school bus and brought a variable geometry turbocharger that doubles as an exhaust brake. By 2019 it produced 400 hp and 1,000 lb-ft of torque. Renamed the B6.7, it ended production in 2026, succeeded by the B7.2 announced in March 2025, alongside a B6.7 Octane that can burn propane or gasoline, the first petrol engine Cummins has built on the B platform.
Source: Cummins B Series engine
