Written By, Mike McGlothlin
Highlights:
The 5.9L Cummins ISB 24-valve, used in ’98.5–’02 Dodge Ram trucks, can reliably reach 500 horsepower with the right upgrades.
Essential performance parts include a tuning module, electric lift pump, larger injectors, upgraded VP44 injection pump, high-flow turbo, and ARP head studs.
Supporting modifications such as a cold air intake, 4-inch turbo-back exhaust, boost elbow, and transmission upgrades improve durability and drivability.
This guide explains how each upgrade increases horsepower, prevents common failures, and extends the life of the Cummins ISB 5.9L.
When it comes to diesel performance, the coveted, P-pumped 6BT Cummins gets all the glory. But while the mechanically injected, 12-valve 5.9L’s ability to produce and support significant horsepower increases on the cheap makes this understandable, its successor, the Cummins ISB 5.9L 24-valve, isn’t exactly a slouch. In fact, it could be reasoned that the ISB engine—best known for its use in ’98.5-’02 model year Dodge Rams—is the better performance candidate of the two. In this article, we’ll confirm the performance viability of the ISB 5.9L by providing a proven path to making 500 hp with your old, 24-valve Dodge workhorse.
Key Horsepower Upgrades
*Tuning module: adds up to 140 rear wheel horsepower (rwhp)
*Electric lift pump: extends injection pump life
*Performance injectors: 100hp to 150hp gains
*Aftermarket VP44 injection pump upgrade: supports higher horsepower and larger injectors
*Higher flowing turbo: supports added power, cools EGT
*Head studs: eliminates potential head gasket issues
Supporting Modifications
*Cold air intake or upgraded air filter
*4-inch turbo-back exhaust system
*Boost elbow
*Upgraded clutch (NV4500 and NV5600)
*Performance transmission rebuild (47RE)
Electronic Power Adder
No different from any other electronically controlled diesel engine, the quickest and
easiest way to unlock more horsepower from the ISB 5.9L is through the use of an aftermarket tuning module. Popular products like the Edge Juice with Attitude from Edge Products and the Quadzilla Adrenaline can take your ’98.5-’02 ISB-powered Dodge Ram from 180 to 190-rwhp (rear wheel horsepower) stock to as much as 320-rwhp. Achieving this 65 to 75-percent increase in power requires you to splice into the VP44 injection pump’s wiring during installation (i.e. “tapping the wire”), but the performance gains can be had without pushing exhaust gas temperature (EGT) into the danger zone (i.e. beyond 1,200 degrees F).
Opening Up The Intake System
Also, not unlike most engine modifications, one of the first 24 valve Cummins upgrades often made is to free up the air intake 
path feeding the turbo. Aftermarket cold air intake systems—complete with a high flow air filter, tubing and, in some cases, a redesigned air box—are readily available and easy to install. However (and contrary to popular belief), a complete aftermarket cold air intake system isn’t mandatory for Rams in the stock to 500 hp range. As such, many ’98.5-’02 Dodge owners opt for the common replaceable open element air filter from Fleetguard known as the Big Honkin’ Air Filter (or BHAF) that carries PN AH1141. The BHAF completely replaces the factory air box and filter.
Freeing Up Exhaust Flow
On the other side of the equation sits the exhaust system, and while upsizing it doesn’t guarantee you’ll produce a bigger horsepower number; a larger diameter exhaust will help support the gains you make with added fueling and airflow. Think of a larger, freer-flowing exhaust system as a supporting actor’s role in an Oscar-winning motion picture. Without it, you don’t have a well-rounded masterpiece that meets your performance goals. On the Cummins ISB 5.9L platform, use of the 4-inch, HX40 style downpipe is highly common, and an aftermarket 4-inch diameter turbo-back system will provide all the exhaust flow you need to make 300, 400 or even 500 hp with a second-gen Dodge Ram.
Electric Lift Pump—A Must-Have For The ISB Cummins
Lift pump failure is both common and the quickest way to kill the 5.9L ISB Cummins’
VP44 injection pump. Once the OEM lift pump no longer supplies the Bosch VP44 adequate low-pressure fuel (at least 5 psi),which provides the cooling and lubricity the pump relies on to properly function, it will begin to fail. For years, aftermarket electric lift pumps have proven the best way to extend the life of the expensive VP44, with companies such as FASS and AirDog offering pumps as well as comprehensive, chassis-mounted lift pump systems. For noise damping and cold-weather protection, an innovative, in-tank, “PowerFlo” lift pump option is also available from Fleece Performance Engineering (shown). Note: the VP44 needs to see 10-15 psi worth of fuel supply pressure at all times.
Larger Injectors
Other than a tuning module, investing in a set of performance fuel injectors is one of the
most affordable and best bang-for-your-buck type of upgrades you can perform on a 24-valve 5.9L Cummins. For 400 hp to 550 hp ISB-equipped Dodge Ram applications, what are labeled as 100 hp or 150 hp injectors are highly common—as are injectors designated according to the nozzle size they’re fitted with (example: 7x.010 or 6x.012). Thanks to their superior durability over VCO style nozzles, SAC style nozzles are preferred by most. The drawback here is that, with the factory turbo still in the mix, EGT is going to climb with larger injectors (and aggressive tuning) fueling the engine.
Aftermarket VP44
Though some ISB Cummins enthusiasts claim the verdict is still out on the performance benefits associated with modified VP44 pumps, we’ve yet to see one underperform on the dyno. Case in point, a Scheid Diesel Lightning VP44 added 103-rwhp to an ’02 Dodge Ram 2500 with no other changes made. On a dual rear wheel 2002 model 3500 equipped with 100hp injectors, the same high output VP44 added 75-rwhp to the truck’s bottom line. And finally, in every instance where we’ve encountered an ISB-powered ’98.5-’02 Dodge Ram making 550-rwhp or more on 150hp injectors, an aftermarket VP44 pump was part of the truck’s horsepower recipe.
Higher Flowing Turbo
To cool EGT back down, as well as add a significant amount of horsepower while doing it,
a turbocharger capable of moving more air is the next logical upgrade. Direct, drop-in turbo options for the ISB 5.9L exist in the form of various factory, Holset HX35W-based aftermarket replacements and Garrett or BorgWarner units. A modified Holset HX35W, complete with a bigger compressor wheel, turbine wheel and/or A/R exhaust housing is a common go-to, as is the BorgWarner S362 SXE or S364.5 SXE. The factory T3 exhaust manifold doesn’t necessarily warrant being upgraded at the 500 hp level.
Boost-Fooling
A boost fooler can be installed on the ISB 5.9L Cummins at any point, but no matter what
one will be needed in order to make more power. Boost pressure will be limited to 21 to 23 psi due to the factory wastegate, but you’ll need 30 to 35 psi (or more) to achieve any meaningful horsepower gains. The boost elbow pictured here (the brass, 90-degree elbow located in the turbo’s compressor housing outlet) is one of the most common solutions for this. It installs in place of the factory elbow, forcing the turbo’s internal wastegate to open later. But not so fast. Due to the higher boost levels this elbow facilitates, significantly more stress can be placed on the head gasket.
Head Studs
With any engine, and especially a turbocharged diesel power plant, additional boost and drive pressure can culminate in a blown head gasket. ARP head studs, with two commonly accepted forms of installing them, are the number 1 go-to solution here. The first method of installing head studs includes pulling, inspecting, and resurfacing the cylinder head, checking the block’s deck surface for trueness, threading in the studs, installing a fresh head gasket, lowering the head back into place, and torquing all nuts to spec. Though unorthodox, the other method of installing head studs entails replacing a factory head bolt for a stud (fully torqued) one at a time, so as not to disturb the factory head gasket’s seal. We can confirm that either method works, especially at stock to 500 hp levels.
The Weakest Link
It’s certainly no arduous task to uncork several hundred extra horsepower from the ISB
5.9L but, depending on which transmission is bolted to the 24-valve Cummins further upgrades will be in store. Ram trucks equipped with a manual NV4500 (five-speed) or NV5600 (six-speed) transmission are easy, with an appropriately rated aftermarket clutch being all that’s necessary to handle the added power (and torque). However, automatic transmissions (namely the 47RE) will require extensive reinforcements to hold up to 400 or 500 hp. The parts list typically includes a billet steel or high-strength steel flex plate, triple disc torque converter, a modified valve body, performance clutch packs, and even a billet input shaft due to the factory unit becoming a liability as early as 400 hp.
