In today's economy, is it worth it to refresh and rejuvinate a worn-down 12-valve?

Published in the April 2009 Issue April 2009 Build, Cummins

Ahh, the 12-valve 5.9L Cummins. Probably the most sought-after diesel power plant when it comes to making big, reliable power. The 1994-98 Dodge Ram was very popular when it was still being built and has continued to be even after 10 years of retirement. None of this emissions stuff, no fancy electrical sensors, PCMs, IDMs or FICMs-just some throttle linkage between your foot and an injection pump. The turn of a screw here, adjustment of some springs there and you're basically on your way to making decent power.

With the recent fuel crisis and price jump in new trucks, we've seen an overload of e-mails and letters from readers looking for ways to get more out of their current trucks. Whether they have fuel mileage or performance in mind, it seems readers just want to see inexpensive and reliable ways to make their older trucks better. We've done builds on a couple Power Strokes, some 24V Cummins stuff and even some extensive Duramax builds. We figured it was about time to go back to the original leader in aftermarket diesel performance, the p-pumped 12V Cummins.

In stock form, the 12V 5.9L was actually a pretty strong competitor in the performance department back in 1994-95, but needless to say, it is falling behind in today's standards. Your average everyday 12V would produce anywhere from 180-215 hp in stock form, depending on which injection pump it was equipped with. It was also very limited in rpms and a useable powerband. However, there is major potential in these trucks and we're here to help you find that hidden horsepower.

Lenny Reed, owner of Dynomite Diesel Performance (DDP) in Monroe, WA, has been around diesel performance for quite some time. His company specializes in performance injectors, injection pump work and aftermarket turbocharger development. DDP has been in the performance Cummins game for quite a while and has built a 12V Cummins powered race truck that produces well over 1000 rear wheel horsepower on diesel only. Needless to say, the company knows how to make these trucks run. So it was a no-brainer when it came time to build up this 1998 Dodge 2500. While our current plans for this truck include extensive injection pump work and some compound turbos to take it past the 550 hp mark, this part of the build looks at the more basic modifications you could accomplish yourself over the course of a weekend in the garage.

Injection Pump Mods

First things first. Let's look at the injection pump mods you can do to improve actual output and capacity. The Bosch P-Pump is a pretty eccentric piece of equipment with a lot of little moving parts that need to be dialed in near perfect if you want it to work to the best of its abilities. Luckily, DDP has done extensive testing and work to put together a list of parts that will do that. While we did all these mods with the injection pump sitting on a bench, they can be done with the pump installed on the truck.

First the fuel plate and android housing adjustments. After removing the factory AFC housing you'll find the fuel plate held down with two screws. It's common for most owners to just slide the factory fuel plate fully forward to improve fueling in the injection pump. Actual performance gains from that will be marginal-10-30 hp at best. DDP has developed a replacement fuel plate with a completely redesigned profile to work in conjunction with aftermarket injectors and other fueling modifications that we'll get into later. The DDP plate profile is cut to decrease fueling at lower rpms, then get more aggressive as boost and rpms rise. The plate is cut back again to decrease fueling at wide-open throttle for EGT control. With today's injector technology pulling fuel out at low rpms, the DDP fuel plate will help control smoke and egts as well.

The 1994-98 12V Cummins came equipped with a few different pumps, the best of which was the 215 hp pump. Our truck is an early 1998 model with an automatic transmission and came with a 180 hp p-pump. On these smaller 180 hp pumps swapping out the OEM Rack Travel Plug found on the front of the pump with one of DDP's deeper plugs can improve actual rack travel from a stock 18 millimeters to more than 21 millimeters. While that increase of 3 mm may not sound like much, Reed said the installation of the deeper Rack Travel Plug can make a noticeable difference in performance.

The next modification we made to our p-pump was with the factory governor springs. These are found under a plug on the side of the injection pump hiding under the throttle linkage. Note: be careful not to lose the small half moon woodruff key found on the post the linkage attaches to. When the plug is removed you'll be able to turn the motor over manually by the crank until you'll see the springs. There will be two sets of springs in the pump. Both need to be swapped out. Replacing the factory springs with the DDP aftermarket parts allows the pump to continue fueling heavy at higher rpms. That means power won't fall off as soon.

DDP makes two governor spring kits for the p-pump: a 3000-4000 kit and a much stouter Comp 5000 kit. While the 3/4K kit would be more than enough for, say the 400-450 hp range, we knew we would eventually be taking this truck farther so we went ahead and installed their 5K kit. When removing the factory springs, pay attention to how many clicks the retainer takes before it's removed. This will help dial in the new springs when it goes together. The factory setup uses four total springs per side while DDP's kit replaces those with just two, which are much stronger than the factory equipment. When the governor springs are reinstalled, be sure both sets of springs are adjusted to the same tension, according to the clicks on the retainer. If the springs are tightened too far you'll experience a major jump in your rpms when it's revved. Too loose and it will make for a slow rev up. Just be sure to tension both sets of springs the same.

Next come the delivery valves. These will require a special tool you can get from your local tool guy. It's specific for the Bosch P-Pump delivery valve application. DDP's new delivery valves will increase pump output by another 50ccs. More injection pump flow means more fuel and more fuel means more power. Swapping these out is pretty straightforward, just be sure to lube the new o-rings when reinstalling to prevent tearing them.

Finally on our list of pump mods is the actual AFC cover and star wheel adjustments. For most, Reed says placing the AFC cover right in the center will get you the closest to dialed-in setup. Adjustment of the AFC star wheel can then be made to fine tune smoke and throttle response. The star wheel is found under the small plug on the top of the AFC housing. Rotating the wheel towards the motor loosens preload and increases low-end smoke, while rotating the wheel away from the motor will increase spring load, decreasing low-end smoke. In the end, this adjustment really comes down to personal preference.

With these modifications made, all parts that most could accomplish in a few hours we've actually doubled total pump output. DDP says the combination of these parts will increase flow by more than 200cc of fuel-not bad considering the stock unit produces just 180cc.


With our injection pump now fueling heavier and providing more fuel in the upper rpm range, it's time to look at improving actual injector flow. For our application DDP recommended its 90 hp injectors. On a basically stock truck these injectors will improve stock output by the advertised 90 hp. However, as more mods are made to the truck, these same injectors could provide enough fuel for more than 500 hp to the rear wheels-perfect for our final goals. The beauty of Dynomite Diesel injectors is in the nozzle work. Through its very precise extrude hone process, these injectors can burn as clean and as efficient-if not better-than stock units, even though they flow a much higher rate of fuel. Installing injectors in your 12V is about as easy as tying your shoes and can be done in just about no time at all.

Turbo And Intake

So now that we've got the fueling side of things wrapped up, it's time to look at providing the engine with more air. While the factory HX-35 charger is a stout unit that is more than capable on a stock 200 hp truck, at say 400 hp, you'd really be pushing it hard and egts could be through the roof. Again with the help of DDP, the company set us up with its new 62 mm single charger, a direct bolt-on replacement that will supply more than enough air to support upwards of 525 hp. The charger is supplied with the needed down pipe and fit and finish on both pieces couldn't be better.

It'll be tough to get past 400-450 hp with our current injection pump setup. So this new charger will flow more than enough air, for now at least. We also installed an AEM Brute Force intake system on the truck to replace the restrictive factory air box. The better flowing paper element filter and direct ducting supplied with the Brute Force not only looks better than stock, it filters better as well. We soon found out after a few hard, full-throttle runs that the new DDP single charger was still almost too much for the AEM intake. The factory filter minder was sucked down around 50 percent after a few hard runs on the dyno. Turns out even a Hoover can't hold a candle to the amount of suction this charger can apply on a high performance intake system.

For now, this DDP 62/71 turbocharger has been developed to provide awesome spool-up and enough air to keep our new and improved 12V running cool. The 62/71 mm should work perfectly for towing applications, while still providing enough umph for you performance-oriented guys.

Killer Dowel Pin

The last thing we had DDP help us out with while we were under the hood of the truck is installing its Killer Dowel Pin mod. In the 12V Cummins engine there is a small dowel pin behind the front cover that has a tendency to work itself loose under the miles and extreme vibration these motors are subjected to. Problem is, if or when this dowel pin works itself completely loose and falls out, it will find itself falling onto one of the front gears of the engine. The gear continues to turn, the pin will bind up between it and the front cover, blowing the side of the cover out. And that's something that can be very expensive and time-consuming to fix. So as a precautionary measure, DDP installed its Killer Dowel Pin, which put a small metal tab in front of the factory pin. This tab will block the pin from being able to come completely out, preventing future issues.

What We Have At This Point

The charger and power comes in smooth and continues to pull hard all the way through the rpm range. After our initial test drive we'd guess our truck's a solid 400 hp to the tires and no matter how hard we pushed it, that pyrometer wouldn't get over 1275 degrees F. That's 400 useable, streetable and very drivable horsepower. Smoke clears up almost instantly, making for clean, efficient power with this combination of parts.

The best part is, you can grow into all of these parts and you've just laid the groundwork to a solid 550-600 hp truck. You're just some internal pump modifications and a little more air away. There's no need to swap these parts out for different ones should you decide you need more power in the future. The injectors will support 550-plus horsepower, the 62/71 turbo can be used as the top turbo in DDP's compound turbo set-up and the injection pump parts will all be used again once the internal mods are made. So no wasted cash and that's always a good thing, right?

Keep an eye out for future issues of Diesel Tech where we'll go a little deeper into the pump, swapping out some of its internal parts for even more flow. We've still got a set of very trick digital AEM gauges to install and we'll be adding a set of Dynomite Diesel's compound turbos down the road as well. We've really only just begun .

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