When it comes to diesel pickup trucks, the big three names have traditionally been Powerstroke (Ford), Duramax (GM and Chevrolet), and Cummins (Ram and Dodge). While each brand and its fans are adamant that their engines represent the best in passenger diesel engineering, the reality is that each one has its merits. That said, there is one characteristic that sets Cummins engines apart: namely, their use of six cylinders instead of eight.

Cummins passenger diesel engines, with the exception of the engine found in the now-discontinued Cummins-powered Nissan Titan XD, are inline-six cylinder engines. That means that, instead of the traditional V-8 design, the cylinders are arranged in one row. This style of engine is popular for semi trucks, thanks to the impressive levels of torque, among other things, that these motors can provide. Cummins has been building passenger diesel engines in this style for Dodge/Ram vehicles since 1989. During the decades that followed, the Dodge/Ram passenger Cummins diesel engine has seen five generations. During the first three of those generations, the Cummins engine had a 5.9-liter displacement.

While the 5.9-liter Cummins has since been replaced by the 6.7-liter version, the 5.9 Cummins holds a special place in the hearts of innumerable enthusiasts. It’s an incredibly solid and versatile engine, and due to these characteristics, it’s common for owners to modify 5.9-powered vehicles in various ways. We were curious to see what upgrades 5.9 Cummins owners recommend, so we checked out some popular forums and fan sites and found four interesting mods. So, here are four of the best upgrades for a 5.9 Cummins, according to owners.

A fuel filter is a vital component for any vehicle that relies on a fossil fuel source for its power. While, in theory, the gasoline or diesel that we use to fill our fuel tanks is more or less clean, in practice, fuel can contain various impurities and debris. That can be especially true for older vehicles or those with dirty or rusty fuel tanks. Impurities and debris can harm your engine and form clogs in the fuel system, like in the lines or the injectors. To combat this issue, automakers built vehicles with fuel filters. Like oil filters, fuel filters are designed to prevent those impurities and other debris from getting into the rest of the fuel system. Most fuel filters are located close to the fuel tank, allowing the gas or diesel to pass through the filtration material before entering the rest of the fuel system.

Upgrading the stock diesel fuel filter is a common suggestion among Cummins enthusiasts, with some stating outright that the stock part is less than perfect. Performing this modification can lead to improvements in things like fuel economy, throttle response, and exhaust gas temperatures. Because there are three generations of 5.9-liter Cummins engines, though, there is a substantial amount of variation in recommended brands.

However, we did notice a few names mentioned more than once. Perhaps the most popular brand we saw was FASS, a company dedicated to building high-quality aftermarket diesel components. Other commonly-mentioned names include Airdog and Baldwin. There are various companies that make these components, and FASS is one of the top-recommended names if you’re making other modifications, while Baldwin seems to be popular for keeping things closer to the stock setup.

An internal combustion engine, like the 5.9 Cummins, requires an exhaust system to filter and expel the byproducts of the combustion process. The system stretches from the engine’s exhaust manifold all the way to the tailpipe and includes things like a catalytic converter and numerous pipes and fittings. Modifying a 5.9 Cummins’ exhaust system is a popular upgrade and can take many forms, but commonly includes things like making the system bigger to improve flow and replacing or deleting various other components.

However, it’s important to note that removing or tampering with your Cummins’ emissions control system components, like the catalytic converter, is illegal. Straight piping — deleting all of the emissions control parts and replacing them with a straight pipe running from the exhaust manifold to the muffler — is a very common mod among diesel enthusiasts. It is extremely harmful to the environment, though, and could land you in hot water with local law enforcement.

Instead, you can opt for legal aftermarket exhaust mods. Some of the most popular mods in this category include upgraded exhaust manifolds, larger exhaust piping, and aftermarket mufflers. There are numerous companies that build exhaust systems designed to replace the stock setup while meeting local guidelines regarding emissions. The biggest thing to keep in mind is the catalytic converter, but it’s also important to consider noise ordinances when upgrading your muffler. Check the local and national laws in your area, and consider visiting a professional exhaust shop for this work, especially if you’re not an experienced home mechanic.

A cold air intake is a common modification for gearheads and enthusiasts of all persuasions, not just those who own diesel trucks. These aftermarket upgrades are designed to replace your stock air intake system, including the tubing and the engine air filter. They typically work by repositioning the air filter farther away from the engine, allowing the system to draw in colder air, which contains more oxygen and enables the engine to burn fuel more efficiently. Depending on your vehicle and the type of cold air intake you buy, you can typically expect to see an increase in horsepower of around five to 15 horses.

When it comes to 5.9 Cummins pickups, many owners contend that the best air intake upgrade is a simple modification of the stock air box. That’s because, according to many Cummins enthusiasts, the stock air intake system is adequate until you reach a certain horsepower threshold. The modification involves replacing the stock air filter and modifying the intake tubing so that colder air enters the engine. However, if you are looking to squeeze some extra horsepower out of your Cummins, a cold air intake is a simple upgrade, and there are a few brands that owners recommend.

Some of the top names we saw mentioned include S&B Filters and Banks Power. Both companies build a variety of products for different makes and models, and they could be worth checking out if you’re in the market for a Cummins cold air intake. Just remember to confirm the part’s fitment before purchasing, and if you’re not an experienced home mechanic, consider buying a repair manual for your model or consult with a professional before installing.

One of the top upgrades for a 5.9 Cummins, as recommended by owners, is a performance tuner. These devices allow you to access the vehicle’s computer or powertrain control module, enabling you to modify certain performance settings, like ignition timing, fuel pressure, the air-to-fuel ratio, and more. Car tuners, sometimes referred to as chips, are a popular modification among diesel enthusiasts, and when used in diesel pickups, they’re primarily designed to help optimize fuel pressure and injection timing for performance reasons.

When it comes to purchasing a tuner for your 5.9 Cummins, you have several options. First of all, there are three generations of the 5.9 Cummins engine, meaning that we can’t say exactly which tuner is best for you without knowing a bit more about your specific truck. It’s also worth noting that installing and using a tuner can be complex and may require a certain level of expertise. Because of this, many enthusiasts choose to visit a professional tuning shop to get everything set up properly or get a custom PCM tune, and that service is worth looking into if you’re not an experienced home mechanic.

That said, there are a handful of tuner brands that we saw recommended relatively frequently during our research. Smarty, a diesel performance technology dealer, was the brand we noticed the most often. Various Cummins owners spoke highly of the company and its tuners, noting that the Smarty tuning platform offers various versatile options for modifications. Besides Smarty, a couple of other brands that owners mentioned positively include Quadzilla and Edge.