Tech Corner: Top Five 5.9 Cummins Mods and Why They Work

Is there anything more American than a Cummins? A hardy engine that responds notoriously well to power adders, the 5.9 Cummins is a definite favorite in the diesel community. And, as a popular engine for hot rodding, the first thing you’ll likely ask yourself upon scoring one of these powerplants is, “What can I do to make even more power?”

So, today, we’re going to take a look at some proven 5.9 Cummins mods, why they work, and what you need to consider when building.

Computer Programmer

Alright, the first thing you will notice every Cummins build has in common is an aftermarket programmer or custom tune. This really doesn’t come as much of a surprise to most of the diesel community. Sure, some argue this is a waste of time, as there are so many other mods you can do that will increase engine performance. However, I still think it’s worth mentioning.

Why? Because even with a base engine, you can reap some serious rewards with an aftermarket programmer. And when you start tackling some of the other recommended 5.9 Cummins mods, you will certainly want an aftermarket programmer to take advantage of them.

With that in mind, selecting the right programmer will depend on what you toss at it. My advice is to take your time and do the homework on what your ultimate goals are, so you can better decide which tuner will help you unlock the most potential with your particular engine. Quality brands like Bully Dog, DiabloSport, Superchips, Hypertech, and ATS Diesel Performance are all great places to start your search.

Upgraded Cams

As the first real upgrade on our list of 5.9 Cummins mods, let’s talk about camshafts. Diesel engine builds almost always surround the concept of upping the amount of fuel and air introduced to the engine. While turbos and fuel injectors certainly make for major gains, they can only help so much without the use of an aftermarket cam. Most mild builds will leave the stock cam untouched. But when you start aiming to produce over 400 hp, it’s a must-have upgrade.

Aftermarket cams are responsible for when, how far, and how long the valves open up. Even with direct injection, this is critical to making sure the right amount of air is being introduced to the burn. It also makes sure the spent fuel can escape.

Hamilton Cams is a popular brand that diesel enthusiasts turn to when they’re looking to harness more power, torque, and pulling strength. Canadian-based Colt Cams, known for its performance and drivability, is a go-to choice as well.

Improved Manifolds

Just like the fact that many Cummins builds won’t be well-supported by the factory camshaft, the same holds true for the factory manifolds. It’s really cool that late-model stuff often won’t need much attention in this area, but unfortunately, the 24-valve Cummins doesn’t fit the criteria.

Factory-cast equipment is built to work, not perform. They will do the truck well with builds up to about 300 hp, but more than that will require some better flow. Hence why swapping the intake and exhaust manifolds is next on our list of worthy 5.9 Cummins mods. This upgrade, paired with a better fuel system will be key to supporting big power builds.

aFe Power, ATS, and BD Diesel Performance are just a few great names to turn to for durable diesel intake and exhaust manifolds.

Bigger Fuel Injectors

What you will find in your studies, is that virtually every Cummins build (at least the serious ones) has fuel injectors thrown in the mix. Even build plans aiming to make a mere 300 hp feature bigger injectors in place of the factory ones. Some suppliers guarantee that adding bigger fuel injectors will increase wheel power by at least 60 hp—even with just the smallest upgrades. Suppliers to consider for your shopping cart are BD Power, Scheid Diesel, and Sinister Diesel.

This is power you feel behind the wheel. And the bigger the injectors are, the more power you’ll gain.

Why is this? With gas engines, just dumping a ton of fuel in an engine that’s not at wide open throttle is harmful to performance—and they have twice the RPM capabilities that diesels do. Well, this is partly because of the turbo on the motor. Consider that the stock turbo size is 62mm, which is absolutely massive in comparison to what you may find on a gas engine. Also, the way the fuel is injected in a diesel engine allows it to make more use of more fuel.

By feeding more fuel into this massively-compressed engine, it’s only natural that you can unlock more power. Though, you can still out-do the factory turbo by adding too much fuel. With the 5.9 Cummins, 50-hp or 75-hp injectors are about the maximum injector size with the factory turbo. (But with the right combination of injectors, intake, and exhaust upgrades—along with a proper tune—a 400-hp build is possible.)

Keep in mind…

Before slapping the biggest injectors and turbo combination possible onto your Cummins, heed some popular industry advice, and upgrade the lift pump. The bigger injector size is going to require more fuel pressure to achieve the power as the stock lift pumps just don’t pump enough fuel. These mods go hand in hand even with the 50-hp fuel injectors I mentioned before.

MORE TURBO

Everyone’s favorite topic in the diesel world and the top of our list of top five 5.9 Cummins mods. Some would even say that a diesel without a turbo is not worth your time. Considering we just talked about how the stock turbos can only support the addition of so much fuel, I feel like it’s a good time to get into the goodness of boost now.

So, with a 62mm turbo already on board, one looking to still hang low with power output might wonder why they should even consider an aftermarket turbo over the stock one. While the 62mm turbo will push tons of air, the factory Cummins turbo has a really small exhaust side. So, with lower horsepower builds, although the turbos are larger, it’s not by a huge amount. Some builders even reach for turbos that use the same intake side but an upgraded exhaust side. Some great names to look out for here are ATS Diesel and BorgWarner.

Keep in mind…

Moving up to bigger turbos will increase power output but will demand more from the engine. Not only will every other mod we discussed need to be made, but also you need to look out and not blow the block to smithereens.

Yes, the 5.9 is notorious for handling serious amounts of power. But if you’re climbing up toward 800 ponies or more, you should definitely entertain the idea of heading to the machine shop to have the rotating assembly beefed up.

At the very least, you will want to take the time to set your Cummins up with aftermarket hardware. Its factory equipment is pretty rugged, but the nuts and bolts that keep everything together can fall short. You should replace them with aftermarket head studs and rotating assembly hardware to make sure the power is properly managed.

You may also know that the factory transmissions often fall short of handling power from a beefed-up Cummins. There are two ways you can deal with this situation if you’re set up with an automatic. You can either have the auto built, which is plenty viable, but you can also make the swap to a beefy manual transmission—which is something we will be talking more about shortly. So, stay tuned!