500HP On A Budget: 12-Valve Cummins Edition

• February 27, 2021
• Story By
  Mike McGlothlin

20 years ago, making 500 horsepower at the wheels was a huge deal in the diesel world. Today, it’s essentially what every mildly-tuned late-model truck makes. Sad, but true. However, what isn’t sad is the fact that older diesel owners don’t have four-digit monthly truck payments or EGR, DPF and SCR emissions system failures to worry about. What they do have is an endless array of proven horsepower recipes to choose from. This is especially true for ’94-’98 Dodge Ram owners, where you’ll find the coveted 12-valve P-pumped 5.9L Cummins between the frame rails. For these trucks, 500 ponies is a number that can be achieved with minimal investment and without killing the engine—even a candidate with 200,000 or 300,000 miles on the clock.

Luckily, at this point the path to 500rwhp is a well-worn one for 12-valve owners. Below, we’ll give you one of many horsepower-making blueprints that has been dyno-verified over the years.

Stock Bottom End, Zero Worries

Getting to the 500rwhp mark requires zero upgrades in the 12-valve Cummins’ rotating assembly, but before you get started stacking horsepower on top of it it’s best to address any issues. You may even need to entertain a re-seal (these things can leak with age) or a compression test before you let the games begin. That said, the factory forged-steel connecting rods will be more than fine (they can handle north of 1,000 hp) as will the OEM cast-aluminum pistons. However, we would advise a pyrometer gauge to monitor exhaust gas temperature, with an added piece of advice to make sure you keep things under 1,400 degrees F as best you can. For optimum peace of mind (or if you happen to be pulling the leaking oil pan off anyway), ARP rod bolts are a great upgrade for the factory connecting rods.

Head Gasket Insurance

Though it’s quite restrictive, the factory cast-iron 12-valve cylinder head will allow you to reach 500 hp, but that aged head gasket might not live at 35-45 psi of boost. For their deeper thread engagement in the block, superior tensile strength and stretch-resistance, ARP head studs are great insurance here. And, instead of pulling the head, having it decked and sourcing a fresh head gasket, the studs can be threaded in one at a time. ARP 425 studs will suffice here (no need to spring for the higher-dollar Custom Age 625+ units) and have been proven more than capable of holding down the fort at more than 1,000 hp.

3K/4K Governor Spring Kit

From the factory, the Bosch P7100 in ’94-98 Ram applications is governed at roughly 2,700 rpm. Worse yet, defueling can start as early as 2,400 rpm. To force the P-pump to fuel to higher rpm and to effectively extend the horsepower curve, higher rpm governor springs are mandatory. Most aftermarket governor spring kits come with both the 3,000-rpm and the 4,000 rpm springs. It’s up to you to decide how fast you want your Cummins to spin. If you plan to upgrade valve springs, which we’ll recommend below, it will pay to install the 4,000-rpm springs.

Stiffer Valve Springs

With higher rpm comes greater potential for valve float. And with elevated boost and drive pressure in the mix there is a higher potential for valve creep. To keep the intake and exhaust valves closed when they should be, stiffer valve springs are highly recommended. One of the most popular valve spring upgrades in the 12-valve segment comes from Hamilton Cams. The company’s beehive springs offer each valve a 165-lb seat pressure and come with the retainers and locks needed to install them. Like head studs, upgraded valve springs can be installed one at a time, just make sure to bring each cylinder to top dead center (TDC) before you dig in.

5-Hole Injectors

Injector selection is a giant market with nearly endless options in the 12-valve world. Depending on the builder, a set of 5x12  injectors (a 5-hole nozzle, each hole measuring 0.012-inch) commonly referred to as 90hp units can get you to 500rwhp with the right supporting mods. Other common injector sizes that aren’t overkill for a 500-600hp application are 5x13’s (+110 hp) and 5x14’s (+145 hp). While there are 6 and 7-hole nozzle injectors in the aftermarket, 5-hole versions are the most proven.

Larger Delivery Valves

You can’t get around performing a few P-pump tweaks when pursuing higher horsepower on a ’94-’98 12-valve Cummins, but luckily either of the P7100’s offered on these engines can easily support 500rwhp (be it a 160hp, 180hp or 215hp version). Sitting between the P-pump and its injector lines sit the delivery valves. Bosch 024 delivery valves have long been an effective upgrade for moderate horsepower levels. Their higher flow allows for a longer duration of the injection event, the obvious side-effect being more horsepower but larger delivery valves also improve throttle response.

AFC Live

Tuning a 12-valve Cummins is all about dialing in the fueling of the injection pump. With its ability to infinitely control the P7100’s fuel rate (by way of rack travel), the pump’s maximum fueling and even for its ability to fine-tune EGT, Power Driven Diesel’s AFC Live in-cab tuner has revolutionized the 12-valve market. Adjustments can be made on-the-fly, which rules out the trial and error that comes with making one mechanical tweak at a time. To well-educated Cummins guys, AFC Live might not be mandatory, but it sure makes life easier. One mod that is mandatory is a timing increase for the P7100. From the factory, most are set with roughly 12-degrees of advancement. Bumping things up to 18-21 degrees makes a considerable difference in power output. Just remember that going much further than 18-21 degrees can lead to hard-starting issues in colder climates.

Supporting The P-pump

While a fresh mechanical (cam-driven) lift pump or a pusher (i.e. helper) pump can get you to 500rwhp with a 12-valve, for utmost peace of mind (i.e. consistent fuel pressure and adequate volume) we would go with a full electric fuel system such as a frame-mounted kit from FASS. Its 140-gph Titanium Signature series system comes preset to deliver 45-psi right out of the box and has proven capable of maintaining that pressure at up to 700rwhp.

62mm To 64mm Turbo

Factory-based Holset turbos and even hybrids can take a 12-valve fairly far into 400rwhp range, but to break 500 you’ll need a little more airflow. A drop-in T3 charger with a 62mm to 64mm compressor will support north of 500rwhp and maintain sufficient drivability. BorgWarner’s T4 S362 SX-E or S363 SX-E units, equipped with the 68mm turbine wheel, will require an exhaust manifold change but are great for this horsepower range also. The SX-E line is known for its quick spool-up, great top-end power and solid reliability while producing more than 40-psi of boost.