Cummins ISB 5.9L 24-valve
Horsepower
235–325 hp
Torque
460–610 lb-ft
Years produced
1998–2007
Aspiration
Turbocharged and intercooled
- Configuration
- I6, 5.9 L
- Aspiration
- Turbocharged and intercooled
- Builder
- Cummins
- Designers
- Unknown
- Years
- 1998–2007
Offered in: Dodge Ram 2500, Dodge Ram 3500
The 24-valve ISB replaced the 12-valve 6BT in Ram pickups partway through the 1998 model year, reportedly to meet updated emissions requirements. It keeps the 5.9-liter inline-six layout but moves to four valves per cylinder and an electronically controlled fuel system. Its ratings climbed through the run, with a high-output version arriving for the 2001 model year and higher-rated versions in 2003 and mid-2004. It stayed in Ram HD pickups until the 6.7-liter engine took over in 2007.
What made it successful
It carried over the 6BT's reputation for durability while offering more power and a fuel system that could be adjusted through software as well as hardware. Its long production run and large parts supply made it a common base for repair and modification work.
Market position
Ram raised the engine's power and torque ratings repeatedly during this period, reaching the top of its own lineup at the 2004.5 high-output rating. How those ratings compared with Ford and GM diesels of the time is not yet sourced.
Rebuild Potential
Tier AEditorial opinion.
The 24-valve has excellent parts and community support and strong output for its size. The 1998.5-2002 VP44 years carry a real fuel-system risk that the fixes only partly remove, so the best candidates are the 2003-2007 common-rail trucks. Keeping the factory emissions equipment in place is required.
Best year ranges
- 2003-2007: Common-rail fuel system, which avoids the VP44 injection pump failure risk of 1998.5-2002 trucks. The exact model-year split is approximate.
Known weak points
On 1998.5-2002 trucks the VP44 injection pump is sensitive to low fuel supply and fails when the stock lift pump does.
Common fix: Replace the lift pump with a reliable aftermarket fuel system and monitor supply pressure with a gauge.
Some early 24-valve engines (1998.5-1999) may share the 12-valve's timing-case dowel pin design, which can work loose.
Common fix: Install a dowel-pin retention (tab) kit.
Common upgrade categories
- Lift pump and fuel system upgrades
- Dowel-pin retention kit on early engines
- VP44 or injector service
- Gasket and rebuild kits
- Cooling and turbo service parts
- Bolt-on intake and exhaust within local legal limits
Keep the emissions equipment the truck was built with. Removing or defeating it on a vehicle originally equipped with it is illegal under federal law. Rules vary by state (for example California/CARB), so check local law and model-year requirements before modifying.
Sources
- Cummins B Series engine (Wikipedia) (accessed 2026-09-18)
- Dodge Ram (Wikipedia) (accessed 2026-09-18)