If you're looking to wake up your truck, a compound turbo for 6.7 Cummins is easily one of the best upgrades you can make to get that perfect balance of power and drivability. Let's be real for a second—the 6.7 is a beast of an engine, but it definitely has its limitations when you start chasing higher horsepower or trying to pull a heavy trailer through the mountains. You usually have to pick between a quick-spooling small turbo that runs out of breath or a big single turbo that takes forever to get moving. Compounds basically tell you that you don't have to choose.
What Exactly Is a Compound Setup?
Before we get too deep into the weeds, let's clear up a common mix-up. People often use "twins" and "compounds" interchangeably, but they're actually different. Twin turbos usually sit side-by-side and are the same size. A compound turbo for 6.7 Cummins, on the other hand, involves two different-sized turbos working in sequence.
You've got a smaller "high-pressure" turbo (often your factory VGT) and a much larger "low-pressure" or "atmosphere" turbo. The big guy sucks in the air first, compresses it a bit, and then shoves it into the smaller turbo, which crushes it even further before it hits the engine. It's like a two-stage relay race where everyone wins. You get the instant spool-up from the small turbo so your truck doesn't feel like a slug at stoplights, and you get the massive airflow from the big turbo when you're really leaning into the throttle.
Fixing the Infamous 6.7 Lag
If you've ever tried to merge into fast-moving traffic with a heavy trailer, you know that "dead pedal" feeling. You mash the gas, wait three seconds for the boost to build, and then you finally move. It's frustrating and, honestly, a little sketchy sometimes.
By adding a compound turbo for 6.7 Cummins, you're essentially filling in that power gap. The smaller turbo is sized to handle that initial take-off, getting you off the line without a massive cloud of black smoke. Once you're moving and the engine RPMs climb, the larger turbo takes over the heavy lifting. The transition is usually seamless—you just feel a constant, linear pull that doesn't seem to quit. It makes the truck feel much lighter than it actually is.
Keeping Your EGTs Under Control
One of the biggest enemies of the 6.7 Cummins is heat. When you're towing a 15,000-pound 5th wheel up a 6% grade, those Exhaust Gas Temperatures (EGTs) can skyrocket quickly. If you're running a single turbo that's pushed to its limit, you're basically just blowing hot air into the engine.
A compound setup is a total game-changer for towing. Because you have two turbos sharing the workload, neither one has to work quite as hard. They stay in their "efficiency map," which means they're moving a higher volume of air without heating it up nearly as much. You'll often see a drop of 200 to 300 degrees in EGTs just by switching to a compound setup. That's the difference between having to back off the throttle halfway up a hill and being able to maintain your speed comfortably while your gauges stay in the green.
Daily Driving and Street Manners
Some guys worry that putting two turbos under the hood will make the truck "touchy" or hard to drive in traffic. It's actually the opposite. A well-tuned compound turbo for 6.7 Cummins makes for an incredible daily driver.
Because the air-to-fuel ratio is much better across the entire RPM range, the truck runs cleaner. You won't be "rolling coal" every time you leave a stoplight, which your neighbors (and the local cops) will probably appreciate. The power delivery is smooth and predictable. It's not like an old-school big single where nothing happens and then suddenly you're sideways. It just feels like a much larger, more powerful engine than what came from the factory.
What's in a Typical Kit?
If you start shopping around for a compound turbo for 6.7 Cummins, you'll notice a lot of "Add-a-Turbo" kits. These are popular because they allow you to keep your factory Variable Geometry Turbo (VGT). The kit usually includes:
- The large S400-frame atmosphere turbo.
- Heavy-duty piping and boots.
- A new exhaust manifold (sometimes).
- Oil feed and drain lines.
- A massive air filter.
The cool thing about keeping the VGT is that you still get to keep your exhaust brake. If you do a lot of heavy towing, that exhaust brake is a lifesaver, and most compound kits are designed to work right alongside it. It's basically the "having your cake and eating it too" of the diesel world.
Supporting Mods You'll Probably Need
You can't just bolt on a massive set of turbos and expect everything else to stay happy. If you're going the compound route, you've got to think about the rest of the truck.
First and foremost: Head Studs. The 6.7 Cummins is a stout engine, but the factory head bolts aren't really meant to handle 60+ PSI of boost. If you don't swap them out for some high-quality studs, there's a good chance you'll stretch a bolt and blow a head gasket. It's a "do it once, do it right" kind of situation.
You'll also need to look at your transmission. Whether you have the 68RFE or the Aisin, more power means more stress. A stock 68RFE, in particular, will not be happy for very long if you're throwing 600+ horsepower at it. At the very least, you'll want a heavy-duty valve body and a better torque converter, but a full build is usually the smart move if you plan on using that new power.
Lastly, don't forget the fuel. To make the most of a compound turbo for 6.7 Cummins, you need enough fuel to actually spin those turbines. A lift pump (like a FASS or AirDog) is basically mandatory, and depending on your goals, you might want larger injectors and a modified CP3 pump.
The Cost vs. Reward Factor
Let's be honest—compounds aren't cheap. Between the kit, the turbos, the tuning, and the supporting mods, you're looking at a significant investment. But you have to look at what you're getting for that money.
If you try to get the same power out of a single turbo, you're going to sacrifice something. You'll either have a truck that's laggy on the street or a truck that runs way too hot when towing. The compound setup gives you a truck that can do everything. It can be a 700-horsepower street machine on Friday night and a reliable heavy-hauler on Saturday morning.
Most guys who make the switch to a compound turbo for 6.7 Cummins say the same thing: "I should have done this a long time ago." It completely changes the character of the truck, making it feel more refined, more capable, and a whole lot more fun to drive.
Final Thoughts
At the end of the day, choosing a compound turbo for 6.7 Cummins is about making your truck the best version of itself. Whether you're tired of watching your EGTs while towing your camper or you just want that "pinned to the seat" feeling when you hit the highway, compounds deliver in a way that other setups just can't match. It's the gold standard for a reason. Just make sure you've got the supporting mods to handle the extra grunt, and you'll be grinning every time you hear those two turbos start to sing.