24 Valve Cummins

Horsepower road blocks

Published in the April 2009 Issue April 2009 Build, Cummins

It has been almost a year since we started this series, discussing how to make 500, 750 and 1,000 horsepower with various factory engines. The more we talk to people, the more ways we find in getting to various horsepower levels. It is amazing that a diesel can reach "X" horsepower 10 different ways. A gasoline can reach "X" horsepower a couple different ways and then there are quite a few different components that work within that recipe. For a diesel, it isn't just a matter of switching to a different component that makes the difference; it could be going in a completely different direction.

Never is this more true than with the 24-valve 5.9l Cummins built between 1998.5 to 2002. In 1998.5 when Cummins switched from the 12-valve to the 24-valve, it redesigned the head, replaced the p-pump with a VP44 (electronically controlled) and made a few other minor changes. This marked Cummins' first voyage into the electronic diesel engine in the light duty truck market.

In the aftermarket, this pump is loved and hated. In recent years, companies have started investing time and money in the research and development of this pump. The results include quite substantial flow increases. From the factory, the engines were rated at 235 hp and 460 lb-ft of torque. The high flowing aftermarket VP44 pumps are now almost capable of supporting 800-plus horsepower on straight No. 2 (No. 2 is in reference to using only pump fuel) and more than 1,000 horsepower with nitrous.

The aftermarket has for many years taken the VP44 injection pump off the engine and installed p-pump conversions (the necessary components to add a 12-valve p-pump). The p-pump conversion is the most popular way to reaching high horsepower with a 24-valve engine.

In addition to the differences in injection pumps, you have those that are hard core, diesel No. 2 power fanatics. Typically these are people who are sled pullers where the rules state no nitrous. On the other side of things, you have those who love nitrous and heavily rely on the additional air supplied by the nitrous to boost the horsepower numbers by 200 to almost 600. These are typically drag racers who have always been allowed to run nitrous and believe it is a safe, cost-effective alternative. Then somewhere in the middle of the spectrum are the people who believe in adding everything they can. So they will be adding the propane, nitrous, water/meth, No. 2, fuel additives and anything else they think they can add to get them where they want to be. We won't be discussing any of those options here, as finding the right mixture is extremely hard and often times massive engine failure results from the wrong combination.

We will simply focus on the most common and popular ways. Where you live and what you do determines how you achieve the horsepower you are trying for. So, what we thought would be the easiest engine in this series of stories to write, actually became one of the most challenging.

We have worked to compile a list of the most common ways of reaching 500, 750 and 1,000 horsepower with a 24-valve engine, but by no means is this the only way possible. We can probably write 15 articles on this and not one will repeat the recipe. Then on top of that, you have the different brands that make each component and before you know it, you are probably talking about more than 100 ways of reaching these goals.

500 Horsepower

Reaching 500 hp with an engine rated for 235 is a challenge in itself. But thanks to the recent diesel boom which we have all contributed to, it is becoming easier to reach. High-flowing intakes and exhaust systems are necessary and are usually one of the first modifications made by enthusiasts. For 500 hp, a 4-inch exhaust is sufficient and available pretty much anywhere.

To handle the air requirements needed for 500 hp, a 64 mm to 66 mm turbocharger is needed. Either turbocharger is capable of handling the air, but the 64 mm is better suited for daily driving, while the 66 is better for a weekend warrior and someone with top-end in mind. While changing the turbo, a higher flowing manifold will help reduce backpressure and lower exhaust temperatures.

For the fuel requirements, an aggressive programmer teamed up with a fuel box make a great combination. Together they tell the pump to stay on and pump out lots of fuel and adjust the timing to make big power. To take full advantage, the VP44 pump needs to be reworked to flow more. So, sending it out to someone like PDR, to have them custom build/modify the pump to flow and support the 500 hp is key. In order to keep up with the fuel demand from the modified VP44 pump, an upgraded lift pump is required.

A good lift pump will flow a very high volume but do it at a high pressure. On the other side of the spectrum are the injectors. They flow very little (relatively compared to a fuel pump) at extremely high pressure. So, to flow the amount the VP44 pushes, 150-175 over injectors are needed.

The stock automatic transmission won't handle this type of power very long, if at all. So, a billet input shaft and an upgraded set of clutches will help to hold the power. Depending on the driving habits of the driver, billet intermediate and out put shafts might be a good idea if the driver demands performance at the push of the pedal. A higher stall converter will help spool the 64/66mm turbo easier and make daily use much easier.

750 Horsepower

Taking the 24-valve to the next level is where most of the differences between builders came from. Many said do a p-pump conversion while others said keep it. For us, we were conflicted.

We decided that readers who were interested in doing a p-pump conversion could re-read our 12-valve road blocks story and use the same basic outline for 750 hp. So, let's talk VP44.

The intake and exhaust systems have already been replaced. The VP pump will need to be sent out to be converted to a Monster Pump. The Monster Pump flows enough to keep the 300 over injectors flowing at their max.

With the fuel now available, it is time to move onto air. If the vehicle is daily driven, a good compound setup with a small charger around 62 mm and a large compressor around 74 mm will provide the air from throughout the rpm range, making driving a 750 horsepower truck daily possible.

The factory intercooler isn't designed to handle this much CFM (cubic feet per minute) of air or the pressure it will be flowing at. Consequently it won't handle it very long. So upgrading to a good aftermarket intercooler is necessary. Most will support around 1200 hp while only having a minimal pressure drop between the inlet and outlet.

With the intercooler now able to support the flow, the cylinder head becomes the next restriction. Cutting the intake manifold off of the cylinder head and having an expert port and polish the head can make all of the difference. Be careful, as many people can port and polish, but few can do it as well as Dealer Machine or other companies who specialize in Cummins' cylinder heads.

While the head is off, upgrading the valve springs will help keep the pressure on the valve, which prevents the valve from floating with high boost pressures and/or rpms. In addition, adding a custom cam tuned for your particular use will help direct the exhaust out and fresh air in when you need it.

Once the air and fuel are in the cylinder, it creates a lot of pressure as it ignites. So, upgrading to a high quality head stud is a must. Some experts recommend upgrading to a 14 mm stud if you already have the motor apart, but not everyone agreed that it was needed at this horsepower level. With the head back on, a sheet metal intake manifold is used to direct the air from the intercooler back into the intake runners.

1000 Horsepower

One thousand hp with a VP44 pump is possible, but only a handful of people in the country have done it. Those that we know of just smile and say it is the same as the 750 hp with a few "special tricks." As to what those tricks are, no one wants to say.

We would assume that the injectors probably need to be custom extrude honed to handle the fuel requirements. Multiple stages of nitrous need to be utilized to help fully burn the massive amount of fuel the injectors inject. The nitrous also helps reduce the exhaust temperatures which, at this level, could get out of control very quickly.

Lowered compression is usually required. Somewhere between 14:1 to 14.5 seems to be a popular range. We would also suspect the pistons have been ceramic coated to help handle the heat. ARP 625 head studs are strongly recommended. The rest of the modifications that are needed, or rather tricks, well, who knows but the select few who have done it?


Dealer Machine

Farmboys Diesel

Texas Diesel Power

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