If you drive a common rail Cummins, you already know it’s one of the most upgrade-friendly diesel engines ever built. Whether you're working with a 5.9 or 6.7, it doesn't take much to wake these engines up. And with the right combo of airflow, tuning, and fueling upgrades, you can safely add 300 horsepower or more at the wheels.
This guide walks through real-world stages of a performance build, from mild bolt-ons to compound turbos and dual CP3s. We’ll break down which parts make the biggest impact, how to avoid blowing your head gasket or torching a piston, and the best upgrade path for your horsepower goals. If you’ve ever wondered how far you can push a Cummins (and how to get there without blowing your budget), you’re in the right place.
Why Add 300HP to a Common Rail Cummins?
Adding 300 horsepower to a common rail Cummins isn’t just about flexing on the dyno. It’s about unlocking real performance gains that you’ll notice every time you get behind the wheel. Whether you're towing, commuting, or just having fun on the weekend, the extra power delivers meaningful results:
- Confident towing at high altitudes. More boost and torque help offset power loss in thinner mountain air.
- Stronger highway acceleration with a loaded trailer. Passing is easier, and you won’t need to downshift as often.
- Improved throttle response off-road. More torque helps turn larger tires and power through rough terrain.
- More fun when daily driving. Whether you’re cruising empty or hauling a load, throttle response and mid-range power feel noticeably sharper.
- Better efficiency at cruising speeds. A well-tuned build can actually improve fuel mileage under light load, thanks to reduced strain on the engine.
Best of all? A 300HP gain is entirely doable without compromising drivability or emissions equipment, as long as you follow the right build path. Let’s break down how to do it, step by step.
How Much Horsepower Can a Cummins Handle?
One of the biggest advantages of owning a common rail Cummins is how much horsepower it can handle before you need to crack open the engine.
The 5.9L Cummins, especially earlier models with forged rods, is known for holding up to 800–1,000 horsepower with proper tuning and careful torque management. Many street builds comfortably push 750HP on stock bottom ends by upgrading airflow, fueling, and monitoring systems.
The 6.7L Cummins, while slightly newer and more powerful out of the box, uses a different connecting rod design that’s known to be more brittle under extreme stress, particularly with aggressive low-RPM torque from tuned VGT turbos. This means it’s smart to keep torque under control, or plan to upgrade rods if you're targeting high-end numbers.
Here’s a rough breakdown of safe power limits without internal engine work:
- 5.9L Cummins: Safe up to 750–800HP on stock bottom end (if torque is managed)
- 6.7L Cummins: Safer to cap around 650–700HP unless you’ve upgraded rods or run a gentler turbo setup
If you want to push beyond these limits, you’ll need to start thinking about forged internals, cam swaps, and block work, which we’ll cover later in the Stage Four section.
How to Increase Cummins Horsepower: Quick Upgrade List
Want the short version? Here’s a high-level look at the best mods to add up to 300HP (and beyond) to your common rail Cummins. Each step stacks on the last, so follow the order below to build smart, avoid rework, and keep your engine safe as you climb the horsepower ladder.
- Cold Air Intake + 4" or 5" Exhaust: ~+30–50HP. Improves airflow, lowers EGTs.
- ECM Tuning (Edge, EFI Live, HP Tuners): ~+100–150HP. Biggest bang for your buck.
- Intercooler + Banks Intake Horn: ~+25–40HP. Reduces charge temps, adds boost.
- Head Studs + Pushrods + Valve Springs: 0HP. Keeps your top end alive under boost.
- Turbo Upgrade (Stock mount or 2nd Gen swap): ~+50–100HP. Better spool, more air, more fun.
- Lift Pump (e.g. Fleece PowerFlo): Supports fueling. Needed once you exceed ~500HP.
- Dual CP3 + Larger Injectors: ~+100–150HP. Required for builds over 650HP.
- Transmission Upgrade or Clutch: Required around 500HP+. Keeps power to the ground.
Total Potential Gain: 300HP+
That means a well-built 5.9 or 6.7 Cummins can reach 700–800HP at the wheels — all while staying emissions-equipped, street-drivable, and fun to tow with.
Start at the Bottom
Starting in 2003, the standard output 5.9 liter common-rail Cummins produced 235hp and 460lb.ft. of torque, and the high-output version of the same year made 305hp and 555lb.ft. Halfway through 2007, the larger 6.7 liter model was released which was rated at 350hp, and brand new 2019 models are available with 400 horsepower and 1,000 pounds of torque, which makes Ram the first automaker to release a pickup truck with a four digit torque rating. If you want to move Mt. Rushmore on the back of your gooseneck, the Ram will get the job done. But if you want to go fast, you need to bump those numbers a bit further.
There are tons of speed parts out there for the Cummins, and it can be difficult to determine which ones you need, and in what order to install them. Depending on who you ask, you’ll get different opinions on what order is best, but one thing is for sure: if you put the cart before the horse, you can certainly do damage to your engine. The horsepower figures we’ll be referring to are all at the rear wheels, and we’ll mostly be dealing with round numbers since every year of truck is different. We’ll go through the steps required to build a stock truck into a monster, talk about the parts needed to make it happen, and why those parts are important.
Stage One: 430HP with Basic Bolt-Ons
Stage One is all about building a strong foundation: more airflow in, more exhaust out, and the right tune to bring it all together. These are low-effort, high-reward upgrades that set you up for future horsepower gains without touching internal engine components.
Even before the warranty is up, most owners will perform what I consider a “stage one” set of upgrades. There is minimal work required, and its all about getting a little more air into and out of the engine. The additional airflow will prepare the engine for a performance tune which is where the majority of the power will come from. You’ve no doubt heard it before, but cooler air is denser, and denser air can make more power; that’s the whole name of the game. A cold air intake system from S&B starts with the largest and freest flowing filter possible and isolates it from engine bay heat in a sealed airbox, which is fed by cool outside air. When combined with a larger and freer flowing intake tube, the turbo will have all the cold air it can ask for, and the engine can operate to its full potential, giving a touch more power and fuel mileage. Plus, you can select a reusable oiled filter, or a dry filter if you prefer.
On the opposite side of the turbocharger, we need to deal with the spent gasses. The stock exhaust system does a great job of restricting flow and keeping noise down, but it’s time to let that Cummins breathe. It’s a very easy job to replace the whole system from the turbocharger to the tail pipe, and it’s smart to install the system which supports the final amount of horsepower the truck will make. There are really two options for tube diameter, 4 or 5 inches. The internet will tell you a 4” exhaust will make more low-end torque since a turbo “needs more back pressure” to operate at low engine speed. I’m here to tell you that’s FALSE. A turbo does not need any restriction, in fact, the less restriction the better. The main tradeoff between the two sizes is sound, and the total amount of power it can support. If you plan on making anything less than 600 horsepower, a 4-inch exhaust will be adequate. However, if you want to run a 5-incher on your near stock truck, there’s no reason you can’t. Just be prepared for a little more up-front cost, a little more weight, and some more noise. Either size you choose will result in an increase in power, lower EGT, and an increase in fuel mileage. A great high flow system which will last throughout all stages of the build would be a 5” MACH Force XP turbo back kit from AFE. It’s made from stainless steel, so you know it wont rust out, has a high flow muffler to keep the noise at a respectable level, and it even includes a polished tip for good looks.
Finally, we get to programming, and this is where the real power gains will come from. The ECM for the Cummins engine has gone through many changes throughout its production run, and each generation requires different “tools” or software to reflash the computer. If you are happy with a “stage one” type of build, a box programmer like an Edge or Bullydog will be all you need, however, if you want to push further, it’s a smart financial move to choose custom tuning which can grow with your build. For 2003 to 2007 5.9 trucks, one of the best custom tuning platforms is HP Tuners, and Ryan Milliken from Hardaway Performance can reprogram your ECM to meet whatever horsepower goals you have, even when starting with a bone stock truck. The best part about custom tuning is as you add more hard parts, it’s very a simple process to update the tune file to keep everything working in balance.
For later model trucks, its advantageous to use the EFI Live tuning platform, since it has the capability to switch between power levels on the fly with an optional switch. Calibrated Power provides their tunes on an Autocal device which you simply plug into the OBDII port and re-flash the computer. Once the CSP switch is installed, you can enjoy towing, daily driving, or racing, all with a clean running truck that gets better fuel mileage than stock.
Stage Two: 550HP - Upgrading Support & Airflow Systems
At this stage, we’re increasing airflow and heat management while reinforcing critical components inside the engine. You’re not just adding power. You’re making sure the motor can live with it.
- Supporting Mods: Head Studs, Pushrods, & Valve Springs
- Airflow & Manifold Upgrades
- Turbo Options: Stock Mount vs. 2nd Gen Swap
One accessory I consider to be necessary after stage one is a good set of gauges, with the two most important being a pyrometer and a boost gauge, as they are the best indicator of the health of your engine, and they give you a warning to take your foot off the accelerator if things get too hot. For a high-tech look you can install an Edge Insight CTS3 using an external sensor for the pyrometer, plus it will allow you to keep an eye on other parameters like injection timing, rail pressure, fluid temperatures, and a whole lot more.
Parts that Support Power
The parts for stage two are broken up into two separate categories: parts that support power and keep the engine together, and parts that add power through increased airflow. As a precautionary measure, I always recommend the “safety” parts first, which means its time to pull the valve cover off and take advantage of how easy it is to work on a Cummins. At a stock or mildly tuned power level the factory head bolts work great, but since it’s so easy for a Cummins to make a ton of horsepower and boost, the stock bolts will run out of strength, which is why it’s very common to see a tuned Cummins with a blown head gasket. To prevent that from happening, its necessary to swap out the head bolts with a stronger fastener, and the industry standard is a set of ARP Head studs. For most street trucks making under 800hp, the ARP2000 (rated at 220,000 psi tensile strength) studs will work great. For higher power levels, you should step up to the CA625 material. This does represent a pretty steep price jump, but the fasteners are rated at a much higher at 260,000 to 280,000 psi. After all, if your combustion pressure isn’t sealed inside the engine, you’re not going anywhere.
The valve spring is responsible for closing the valve, but it also has to push a rocker bridge, rocker arm, pushrod, and a tappet back down to the base circle of cam. There is a lot of mass to move, plus you have boost and exhaust drive pressure pushing against the backsides of the valves trying to work against the spring. When you combine that with higher RPM, the stock valve springs have a hard time keeping up, and if they cant close the valve in time, the piston will step in and do the job instead, which is not what you want to have happen. To keep the valves where they belong, stronger springs are in order, and it’s an inexpensive and worthwhile upgrade on any tuned Cummins. Hamilton 103 Pound Valve Springs will work much better than the stock 80-pounders and will keep the valves in place without putting too much pressure onto the cam lobes. Since you already have the valve cover removed to install the head studs, valvesprings will only add another hour or two to the job. The final upgrade I’d do while under the valve cover, is stronger pushrods. Since they are so long and made from thin wall tubing, the stock pushrods can bend due to the stronger valvesprings and elevated cylinder pressure, so an inexpensive upgrade to Hamilton Extreme Pushrods will keep you out of trouble. It will cost $630 for both valvesprings and a set of pushrods, but its honestly cheap insurance.
Parts that Add Power
Now that the valvetrain is stabilized and the head is clamped to the block, its time to add a bit more air into the mix. On the driver’s side of the engine, the stock intake horn is very restrictive and only flows 432 CFM of air which becomes a bottleneck, so an easy and inexpensive solution is the Banks Monster Ram Intake and larger boost tube. You can get 3.5- or 4-inch version for your Cummins which will flow up to 1,008 CFM, feed more air into the cylinders, lowers air temp, and actually raise boost pressure without creating any additional exhaust back pressure.
It’s always smart money to upgrade the intercooler during stage two to pull more heat away from the air headed to the engine. The stock intercooler will flow a bit more than it was designed to, but once the boost is turned way up, the stock core becomes a restriction, creates a pressure drop, and is less efficient at removing heat. An AFE Bladerunner can flow 30% more air than stock and has 3/16” TIG welded end tanks, and since its rated at 200 psi it can handle any amount of boost you can pump into it.
Turbo Time
The turbocharger is very important when it comes to making power, and of course for stage two and beyond you’ll need a larger one, but the big choice is what type. When it comes to picking turbos for the Cummins, there are two separate schools of thought: those who recommend a 2nd gen swap, and those who prefer a stock 3rd/4th gen style. Each has its pros and cons, but first let’s explain what it all means. Common rail trucks from 2003 onward (3rd and 4th generation body style) mount the turbine housing between the 4th and 5th cylinder with the manifold discharge pointed straight down. This puts the turbo much lower in the engine bay and closer to the block. Though the manifolds from the 5.9 and 6.7 look nearly identical, they are slightly different. The 5.9s used a standard T3 flange, and the 6.7s used a slightly larger (but not T4) flange with the VGT charger. In both instances, the runners inside the manifold are restrictive, and the placement limits what turbochargers you can physically bolt up. A second gen swap will ditch the stock design, and instead uses an exhaust manifold designed to fit a 2nd generation 24-valve Ram from 1998.5 to 2002, where the turbine is centered between cylinders 3 and 4, and the manifold has more symmetrical look with even airflow between all the cylinders. The turbo is mounted higher and further away from the engine, which means you can install a larger and more durable S400 style of turbo, with plenty of size options for a range of power levels.
For simplicity sake, you can stick with the stock turbo placement since you’ll be able to re-use the exhaust system and cold air intake you already have, but the manifold itself should be swapped out for a higher flowing replacement like the BD-Power 2-piece exhaust manifold. It’s a direct replacement, will work with your emissions equipment, flows much better, and is made from a much thicker and more durable material so it won’t crack like the stock versions do. For the needed airflow, it can be paired with a BD-Power Screamer turbo, which is a modified VGT with a 64.5mm compressor wheel which will support nearly 700hp and still have excellent street manners and spool up, along with turbine braking ability which is a must if you still use your Ram to tow. If you want even more power potential without losing spool up or drivability, you can also add an Industrial Injection Add-A-Turbo Kit on top of your BD Manifold and Screamer turbo. It works in conjunction with a stock or modified VGT, still allows for all emissions components to operate, and you can install it in an afternoon with basic hand tools. If you have compounds on stock fuel with the supporting mods like studs and valvesprings, you’ll have almost no chance of hurting your engine, but you will max out around 550hp, since you’re fuel limited. But whenever you add more fuel later on, the compounds will really come into their element.
2nd Gen Baby
So, what about that 2nd gen swap? It too has its place, but you have to be willing to give up a few things, most notably, the stock variable geometry turbocharger and its wide power band, but if you’re chasing a quadruple digit power number, it’s a sacrifice you’ll have to make. One major factor for deciding between the two styles is driver preference. Some love the feel of a larger single charger, because instead of a smooth linear spool up, it’s a violent rush of power that hits all at once, and admittedly it’s a blast to drive. To get that S400 installed, you’ll have to ditch your stock manifold and turbo and start with a BD Iron Horn Series Turbo Kit. It can be configured in a variety of ways with your choice of manifold and turbo, but for a mild street build you could start with an S363 and cast manifold, or if you want to go nuts you can swap to an S369 SX-E . This means a single S475 is possible, but you wouldn’t want to run that on stock fuel since the spool up time would be pretty long. But whatever option you choose, stage two is all about getting more air into and out of the engine with less restriction, which paves the way for stage three.
Stage Three: 750HP
By now, you’ve stabilized the valvetrain, upgraded the turbo, and laid the airflow groundwork. But if you want to hit 750HP and beyond, it’s time to tackle fueling — from lift pump to injectors — and understand the limits of your bottom end.
By now the head is clamped down tight, the valvetrain is stable, and there is plenty of cool air making its way into the engine, so the only thing missing is fuel. With the groundwork laid, it’s time to test the limits of your engine. The common-rail inline six has by far the strongest stock internals of the big three, but it’s far from indestructible. The earlier 5.9 sits at the top of the heap, and if a larger single turbocharger is used and low RPM torque is kept to a reasonable level, the connecting rods can survive in excess of 1,000hp. The later 6.7’s used a slightly weaker and more brittle connecting rod, and when combined with a VGT and aggressive tuning, massive low RPM torque can cause the rods to split and window the block, which is a very catastrophic (and expensive) failure. If you insist on low RPM boost and torque, a budget friendly upgrade is to install some shot-peened 12-vave connecting rods in your 6.7. Either way, a conservative number to shoot for would be between 750 horses and less than 1,400 pounds of torque at the wheels, and to get there we need a lot more fuel than the stock parts can supply. So, let’s start at the tank and work our way forward to the engine.
- Fuel System Upgrades: Lift Pump, CP3s, Injectors
If you own a Ram, the easiest and simplest way to upgrade the lift pump is with a Fleece Powerflow in-tank lift pump assembly. It installs as a direct replacement to the stock pump and sending unit but has two electric fuel pumps mounted in the bucket. It will flow enough to support 800 horsepower, and will even work with a dual CP3 configuration, but the best part is since the fuel pump sits inside the tank, it requires no drilling to sump the tank, and its very quiet.
When it comes to high pressure fuel, the stock CP3 will throw in the towel somewhere around the 550hp mark. Although you may not need all 1,000hp worth of fuel, the most economical solution is a Deluxe Fleece Dual CP3 kit. It mounts a second belt driven CP3 pump to the engine and comes with a stock displacement CP3K pump which has been modified to supply fuel above 3,000 RPM. And because the fueling duties are now split between two pumps, each has much less work to do, so they will last for a very long time. And if one ever fails, you can simply replace it with an affordable stock displacement pump, rather than a pricey stroker CP3.
Finally, the valve covers need to come off one more time so we can throw some larger injectors into the engine. When choosing injector or nozzle size, you’ll want to keep your overall power goal in mind, and for that 800whp target, you’ll need about 80 percent more fuel than stock, and a BD-Power 180hp injector set will be just the ticket, since they flow 93% more fuel than stock, which wraps up stage three. This is what I would consider to be the upper limit of a “practical” hot street build. At this point you’ll still be able to drive the truck daily, tow a mild load, and have a ton of fun all at the same time. You can push things further however….
Stage 4: No Limits
Built trucks pushing 2,000HP aren't just dyno queens—they're engineering showcases with blank-check budgets. While most readers won’t go this far, it’s worth understanding what separates a 750HP street monster from a competition-ready machine.
Remember the trucks we talked about from the UCC? With seven rigs proving you can make over 2,000hp you can guess where this is headed, and that’s a blank check. Yes, you can take your regular 250k mile Cummins engine to the extreme, but all the parts we had for stage one, two, and three will be thrown out, and we need to start over. The engine has to come out to install stronger pistons and rods, custom machine work will need to be done on the head for more airflow, you want to throw in a larger cam, massive turbos, fire hose injectors, and a couple 14mm CP3 pumps fed by a pair of 200gph+ lift pumps. Is this all practical? Not exactly, but the better question is how fast do you really want to go?
Transmission Upgrades for Cummins Power Builds
Even at the 600HP mark, the factory transmission becomes a liability. No matter which powertrain you’re running—automatic or manual—your drivetrain needs to be just as dialed in as your engine. Here's what to know before you blow it.
68RFE (Automatic)
The stock 68RFE typically taps out around 450–500HP before reliability issues become common. Pushing toward 600HP? You’ll need serious upgrades. Depending on budget and goals, you can go two routes:
- Upgrade your existing transmission with components like BD’s Thermostat Bypass, deep sump trans pan, billet channel plate, triple disc converter, and upgraded shaft kits.
- Replace it entirely with a built 68RFE transmission designed to handle higher torque and towing stress.
G56 (Manual)
If you're running the 6-speed G56 manual, the clutch is your weak point. Once you cross the 500HP threshold, stock clutches tend to slip—especially under load. A South Bend Street Dual Disc Clutch is a common upgrade that can handle serious torque without killing driveability.
Aisin (Automatic)
While there’s less aftermarket support, Aisin transmissions have proven to hold their own at around 600HP. Just know you’ll have limited options if something goes south. At minimum, consider a thermal bypass upgrade and stick to moderate tuning.
Is a Rebuilt or Built Cummins Worth It?
Most owners stop at bolt-ons. But if you’re chasing big power (or rebuilding an aging platform), it might be time to ask: Is a built Cummins engine worth it?
Here’s when a full engine build (or reman) makes sense:
- You’re already pushing 600HP+ and want to go further without risking rod failure or piston damage.
- You’re rebuilding a high-mileage engine and want stronger internal components for longevity and peace of mind.
- You want to futureproof your truck so you can add more power later without tearing it apart again.
A built or remanufactured Cummins long block gives you the chance to:
- Upgrade connecting rods, pistons, and bearings for high boost pressure
- Balance and machine the crankshaft for smoother operation
- Add a performance camshaft and ported head for better airflow
- Start fresh with zero hours on the block
If your goals are north of 750HP or you’re planning compounds, a built bottom end isn’t optional — it’s the foundation.