Limitations, Concerns, and Supporting Mods
The limitations of the 47RE and 48RE automatic transmissions are relatively high and quickly realized when modifying the Cummins turbodiesel for greater performance. Basic add-ons like an aftermarket exhaust or air intake system are unlikely to necessitate the need for transmission upgrades, but even mild tuning can put you at risk. The level of concern depends considerably on the mileage of the transmission and if you plan on any major upgrades, don't ignore the weaknesses of the drivetrain. The Cummins has been known to snap input shafts with as little as 500 rwhp, so if your goals put you anywhere near this marker expect to stuff the transmission full of go fast goodies.
Manual transmissions hold up well but the factory clutch is not going to like your performance upgrades. You'll want to go aftermarket with a unit that is rated for your power range. Every major brand has a tiered product line, letting you choose a clutch that balances price, performance limits, and clutch pedal feel.
Head Stud Considerations - When Does My Cummins Need Head Studs?
The factory head bolt design has been known to be extremely reliable on the 5.9L and 6.7L Cummins. However, high boost levels and aggressive tuning can still blow a head gasket with ease. Some trucks may run 45 psi with factory head bolts and no problems, while others may blow head gaskets at only 35 psi of boost. The amount of boost you make before you're at risk for blowing a head gasket varies. To eliminate confusion, high boost does not directly cause heads to lift, but if you've got the fuel to match this airflow, then cylinder pressures may be high enough to cause concern. Upgrading your head gaskets and installing head studs is cheap insurance if you will be running more than 40 psi. In the 40-50 psi range (with fuel to match) on factory hardware, you're playing with fire.
Monitoring Exhaust Gas Temps
A pyrometer is highly recommended in any considerable performance build. A leading cause of catastrophic engine and turbocharger failure is excessive EGT. Trucks do not come from the factory with a pyrometer. Install a pyrometer so that you can monitor exhaust gas temperatures and avoid the danger zone. The ideal mounting location for the thermocouple (probe) is before the turbine housing inlet; the outlet temperature will be significantly lower and is not necessarily of use for the purpose of protecting the engine from damage.
Lift Pump Reliability Concerns
The factory lift pump (low pressure fuel pump) on the 24v Cummins has an expected lifespan of ~100,000 miles and is limited in terms of fuel supply potential. Aggressive tuning, bigger injectors, and other fuel system modifications can greatly decrease the life of the lift pump. Additionally, an injection pump can be damaged if fuel supply demands are not met. A high flow, performance oriented lift pump is therefore highly recommended on these models and is cheap insurance against more expensive repairs down the road.
Valve Float Concerns
Valve float has been known to occur in engines operating near the 50 psi territory in terms of turbocharger boost. This is a relatively high boost pressure for street-able trucks, but worth noting. 12v engines, which can be modified to reach revs greater than the factory design intended, can experience valve float at stock boost levels at engine speeds as low as 3,400 rpm. Heavy duty valve springs are available for all 5.9L engines (12v & 24v) that accommodate greater boost pressures and higher engine speeds.
Killer Dowel Pin (KDP)
The killer dowel pin or simply KDP is of great concern on all 12 valve Cummins engines (1989 to 1998.5 model years). On these engines, a dowel pin is pressed into the engine block that aids in the assembly process by aligning the timing gear housing to the block. The problem is that this dowel pin can dislodge over time as a result of engine vibration. When it makes its plunge from the top of the timing gear system to the bottom of the housing, a number of catastrophic events can occur should the pin become lodged between any pair of the gears in the timing system. It is believed that this risk becomes greater as power is increased. The good news is that the aftermarket has responded with dowel pin elimination kits and they are relatively inexpensive. The bad news is that the installation of such kits is rather intrusive and labor intensive. Regardless, investing in a KDP elimination kit is a no brainer for 12v owners who wish to protect their engine.
53 Block Castings
The # 53 block casting problems affects a large number of 1999 to 2001 model year 24 valve Cummins engines. These block castings are significantly weaker than earlier and later production units. They feature a particularly thin water jacket and are susceptible to cracking. These cracks can then propagate to several inches long and will leak engine coolant. At stock performance levels, problems with 53 block castings are relatively low. However, as performance increases, the potential to develop a crack becomes a greater concern. If you find yourself with a 53 block and are looking to build more power, take this into consideration.
All models of the 6.7L Cummins turbodiesel feature an exhaust aftertreatment system that includes, at minimal, a diesel particulate filter (DPF). Major fuel system modifications, including aggressive tuning, large injectors, and fuel pump modifications, may increase the risk and occurrence of DPF clogging. Any upgrade or modification that causes the engine to produce more soot will not be compatible with these engine unless the DPF system is discarded. Removal of the DPF is illegal under Federal law for vehicles driving on public roads, as is tampering with any emission control component. A DPF delete, though intended for off-road use only, will provide significant improvements in fuel economy, reduced reliability concerns, and open the door for greater performance modifications.
EGT- How hot is too hot?
For daily drivers, tow rigs, or street driven trucks, you should not exceed 1250 degrees F and should not maintain 1200 - 1250 for extended periods of time. Some will argue that the engine/turbocharger can take more than this in short bursts, but we feel there is no need to push the limits and prefer to take a conservative approach. Excessive exhaust gas temperatures do not cause "minor" damage - it'll be an expensive bill. Under load, try to keep you exhaust temps between 1000 and 1200 degrees F. If you're EGTs are unmanageable, you have too much fuel and/or not enough airflow. Look into an upgraded turbocharger, or install a water injection system to keep things cool when you decide to mash the skinny pedal. For race rigs, it all depends on how the engine is built. Some race trucks hit 1800 degrees F during a 1/4 mile run, but don't expect to do that in your daily driver.
General Performance Recommendations (All Cummins Engines)
Intake/Exhaust - Intake and exhaust system upgrades should always be the first step. For an exhaust system, look into a kit that replaces every inch of the factory exhaust from the downpipe to the tailpipe. When installing intake upgrades, don't neglect the air horn. It's not included in air intake kits, but is worth upgrading while you're under the hood. The goal of intake and exhaust mods is to reduce pumping losses by replacing restrictive factory bends and kinks with smooth transitions. With regard to intake kits, "cold air" is typically a marketing spell; select a kit that promises superior filtration above all else; the performance benefits will follow.
Tuners/Programmers - Applicable to all 5.9L 24v and 6.7L Cummins engines, tuning can unleash extraordinary horsepower and torque gains. A tuner (other names include programmer, module, etc) works by modifying the factory engine calibration, altering injection timing, duration, maximum fuel delivery, and additional parameters. These devices are available in an abundance of settings, ranging from mild increases for fuel economy and towing to wild increases for racing and sled pulling. DPF equipped trucks will have more limited options, as high performance tunes will cause particulate filter clogging. Read and understand the manufacturer's warnings, and consider the fact that extra power translates into increased stress on drivetrain components when selecting one of these devices.
Injectors - Larger injectors flow more fuel, it's that simple. Injector upgrades are readily available for Cummins engines. It's best to speak with the injector manufacturer before choosing a set, as they can provide recommendations based on your current/future upgrades as well as the intended use of your pickup. Bigger is not always better; you'll want a set of injectors to match the airflow characteristics of your engine.
Intercooler - An upgraded intercooler typically has a low cost-to-performance ratio, but can help with exhaust gas temperatures by reducing intake air temperatures. For these reasons, most owners do not upgrade the intercooler as a first step in their build. However, the upgrade is nonetheless valuable.
Heater grid delete - In case you missed it, the Cummins engine does not use a traditional glow plug system. Rather, it uses a single "heater grid" in the intake tract. For most owners, this restriction is negligible and isn't a huge source of power loss. However, in all-out performance applications, the heater grid is usually deleted in favor of enhanced airflow. This is obviously not an ideal modification for the average truck, as cold starting will become difficult and likely impossible in extremely cold conditions. It is worth noting that the 6.7L Cummins suffers the worst from the heater grid restriction. It is a 6.7L engine with the valvetrain and therefore breathing characteristics of a 5.9L. Fortunately, there are aftermarket heater grid upgrades that do not delete the system, but reduce its restriction without negatively impacting cold start efficiency.
Turbocharger - The factory Cummins turbocharger leaves much to be desired in high performance applications. There are no shortage of aftermarket turbos on the market that will reduce lag considerably and improve airflow overall. If you have performed or are considering performing major fuel system upgrades, especially big injectors, you'll want to address the factory turbocharger to maximize gains and keep EGTs within a manageable range.
12v Cummins Performance
VE44 Power Pin - For 1989 to 1993 model years, the 12v Cummins used a VE44 injection pump. While not as potent as the later P1700, swapping out the "power pin" is an affordable way to gain 20 to 30 horsepower. Aftermarket power pins replace the factory pin (which controls the fuel flow rate) and have a more aggressive geometry, essentially increasing maximum fuel delivery. There are many designs on the market, and a quality pin shouldn't run you more than $150.
P1700 Delivery Valves - Delivery valves are located within the P1700 injection pump found on 94-98 12v Cummins turbodiesels. The delivery valves, or "DVs" for short, serve as check valves for the fuel system, but also play an integral role in injection duration. Upgraded DVs typically create a sharper injection event with increased duration, which translates into greater power (or more realistically, power potential). Several stages of delivery valves are available, but don't get greedy; opting to install competition DVs on a truck that is used regularly as a tow rig or needs to remain street-able isn't necessarily a wise choice.
P1700 Fuel Plate - The fuel plate, or fuel stop plate, is another option for 94-98 12v Cummins. It controls fuel flow and upgraded designs allow the P1700 injection pump to simply flow at a higher rate. It's inexpensive and can result in gains of more than 100 horsepower, though a conservative 30 to 50 horsepower increase is more realistic for most street driven rigs.
Intercooler - An intercooler became standard for the 12v Cummins for the 1991 model year. For 1989 and 1990 model year pickups, consider installing an intercooler for cooler EGTs and better overall performance. For the factory intercooled 12v Cummins, a more efficient intercooler will prove beneficial for engines with moderate to heavy fuel system modifications as the cooler, denser air charge will increase overall performance potential and help alleviate and/or prevent problems associated with high EGTs.
Killer Dowel Pin Warning - Don't assume that luck is going to save you from the "Killer Dowel Pin". If you're modifying your 12 valve for more power, you'd might as well invest in a KDP eliminator kit. It's cheap insurance against the possibility of a complete engine failure due to a simple, 50 cent metal pin vibrating loose from the front of the engine block.
24v Cummins Performance
J Hook - The J hook upgrade is applicable to the 2001 and 2002 model year 24 Cummins. The device uses a spring connected to the wastegate lever in order to control the maximize boost pressure at which the wastegate opens. Aftermarket hooks hold the wastegate closed longer, thereby allowing for higher boost pressures. The modification is not only inexpensive, but has proved relatively safe and reliable.
Lift Pump - A lift pump is an electric fuel pump that brings fuel at low pressure to the high pressure injection pump. If you've got a 5.9L common rail Cummins, you should feel lucky to get 100,000 miles on the factory lift pump, as this is a common failure. Fueling modifications, via tuning or mechanical means, put additional strain on the lift pump and reduce its longevity. Most recommend replacing the lift pump with an upgraded model when performing modifications. At the very least, install an aftermarket model when the original fails; they are much more reliable.
53 Block Warning - The #53 engine blocks have weak castings around the water jackets, which are susceptible to cracking. The truth of the matter is that many of these blocks will never experience cracks and many owners likely don't even know they have this less desirable block casting. However, increasing the performance of your engine, and therefore the theoretical stresses on the engine block is likely to increase the risk of cracks forming and propagating. If you have a 1999 to 2001 Cummins, check to see if you have a 53 block casting and seriously reconsider your performance goals accordingly.
6.7L Cummins Performance
DPF Delete - The 6.7L Cummins is equipped with a diesel particulate filter. The device contributes to poor fuel economy and reduced performance, but more importantly can become clogged with soot once owners start tuning for more power. Delete kits are widely available, but are restricted to off-road use only. As such, we can only suggest this modification for off-road applications, as removing this emissions control device renders a vehicle illegal for highway use.
Injectables (All Cummins)
Water Methanol Injection - Water methanol injection is a popular performance modification as it provides a noticeable power increase, but more importantly it reduces EGTs by cooling the incoming air charge. The ratio of water methanol solutions can vary from 100 percent pure distilled water to a 50/50 mixture of water and methanol. A pure water mixture produces maximum cooling effects, while a water/methanol concentration provides cooling effects and additional power. These systems are perfect for keeping exhaust gas temperatures in check while pulling long grades, maximizing fuel economy on long trips, and everything in-between.
Diesel Propane/CNG Injection - Diesel propane injection (DPI) and CNG injection are somewhat of a controversial modification that has become increasingly less popular in recent years. Opponents argue that there are too many risks, and that there are alternative modifications that provide greater benefit. Proponents are quick to point out extremely high increases in fuel economy and a noticeable performance enhancement. Some evidence suggests that propane/CNG injection is perfectly safe, but only if you plan to avoid additional modifications (tuning, fuel mods, etc). Most tend to agree that this is not a recommended modification for towing or other high-load scenarios, as the risk of detonation grows with engine load.
Nitrous Oxide - Nitrous Oxide is literally a combination of the elements nitrogen and oxygen. Therefore, the benefits of nitrous oxide are more oxygen (as it is injected directly into the intake) and cooler intake air temperatures (resulting in a denser air charge). Though nitrous oxide injection has been associated with destroying gas engines, it is relatively safe for diesel engines when using a properly sized kit. To the best of our knowledge, nitrous is illegal for highway use in all 50 states, but rumor has it that some locations allow for the tank to be installed granted that the bottle is turned off while on public roads. Check your local laws before proceeding to install a nitrous oxide injection kit. Regardless, nitrous is not something you use routinely - it's best suited for use in short bursts, perfect for the drag strip or sled pulling events.