One Cam, 24 Valves
By 1998, Cummins had mastered pushrod-operated non-adjustable four-valve cylinders, and the layout was applied to the 5.9L and the engine was labeled ISB (Interact System B-series). The ISB engine also brought stiffer exhaust valvesprings (for use with exhaust brakes), a new two-piece exhaust manifold, a Holset HX35 turbo with wastegate, a larger oil pump, and a stiffer block. To quiet the new engine, noise-reduction techniques were applied to the valve cover, front covers, and oil pan.
The ISB was fueled by an electronically controlled VP44 rotary injection pump with central injectors. These engines are thought to be the noisiest Dodge Cummins yet, in part because minimum idle speed was computer regulated and not easily lowered as on earlier trucks. The VP44 rotary pump developed a reputation similar to that of the first Getrag gearboxes: more than adequate for stock use but not the best for tuning or running much power through.
DaimlerChrysler's warranty division has boxes of failed injection pumps that were paid for by the customer because the trucks had been chipped. The VP44 injection pumps often fail when the factory electric lift pump cannot supply adequate fuel to it. One of the first recommended accessories for these models is a fuel pressure gauge, because when the factory lift pump goes bad, it's usually not long before the much-more-expensive injection pump goes, too.
We should also note that '99-'00 trucks had the less desirable "code 53" blocks, which were prone to cracking on the rear passenger side. Investigate before investing in that engine.
For 2001, Dodge introduced a new manual gearbox, the NV5600, which was built like a tank and weighed even more than the optional automatics. This extra weight is the reason the towing capacity rating on some of the earlier higher-powered six-speed trucks was actually lower than on the earlier five-speed versions. An NV5600 could give you blisters shifting when it was new, but it had a short action and the stout construction to handle the new high-output HO Cummins engine that became optional.
With one engine power rating for automatic transmission and five-speed trucks, the HO engine added 10 hp and the biggest jump in torque yet (45 lb-ft) to 505 lb-ft. To handle the extra power, a host of changes (like piston cooling) were added to the engine to ensure durability.
High Pressure Common Rail
Common-rail injection went on European Cummins engines in 2001 and the Dodge Cummins for model year '03, bringing much less noise, more power, and lower emissions. Despite the engine being more efficient, a heavier truck, bigger tires, and other factors conspired to drop real-world fuel economy slightly.
Most bottom-end hardware was the same as on the previous 24-valve engines, but the block was stiffened and given a bedplate. The redesigned head got hardened valve seats (intake and exhaust), a new front gear train, a modified HY35 turbo, a 3-1/2-inch exhaust, a crankcase vent system, a belt-driven power steering pump, and electronic control of the viscous fan clutch drive.
Torque peak dropped from 1,600 to 1,400 rpm for better off-idle grunt, while 50-state emissions trucks got another 15 hp and 200 rpm for 250 at 2,900. All the engines ran 22-24 psi boost, and the quiet and wider operating range were the primary advantages to the driver.
The HO model was upgraded with cracked-cap forged rods (still six-speed manual only), and bumped power output 60 hp and 50 lb-ft to 305 hp at 2,900 rpm and 555 lb-ft at 1,400 rpm, respectively. For the mid-'03 models, the HO became available with an automatic transmission, the 48RE, and the five-speed manual and 47RE four-speed automatic fell off the option list for 2004. You still couldn't get an HO Cummins in California.
That all changed on January 1, 2004, with the mid-'04 model "Cummins 600." Inconel valves and high-cobalt content Stellite exhaust valve seats complemented revised ports with less swirl, a bigger turbo compressor wheel, and electronic wastegate control for the HY35 turbo. To feed all that power, a new fuel lift pump and intake air heater that needed no ground strap found their way into the engine. This brought the top engine rating to 325 hp at 2,900 rpm with 600 lb-ft at 1,600 rpm, thanks to 30 pounds of boost-regardless of transmission or state the truck was sold in. For 2005, the torque rating was bumped to 610 to keep it ahead of GM's Duramax LLY engine that received 605 lb-ft rating.
The high-pressure common rail has proven reliable, although a few have found that even this injection system has limits when it comes to "black box" upgrades.