Why the 6.7 Cummins Is the Go-To Tow Truck
Torque characteristics that suit heavy towing
The 6.7L Cummins is a long-stroke inline-six that builds big torque at low RPM — exactly the power delivery heavy towing demands. Instead of revving to make power, it pulls hard right off idle, which keeps a loaded trailer moving up a grade without hunting for gears. That low-end grunt, plus a stout rotating assembly, is why the 6.7 Cummins has earned its reputation as one of the best heavy-tow platforms on the road.
Where factory emissions equipment hurts towing
The engine isn't the weak point — the factory emissions stack is. Under sustained towing load, three things work against you: the DPF (diesel particulate filter) fires forced regens that dump fuel and spike exhaust temps at the worst moments; the EGR system recirculates hot, soot-laden exhaust that fouls the intake and stresses a failure-prone EGR cooler; and the added backpressure and fueling overhead quietly cost you MPG. For a tow truck, that's the stuff worth fixing first. Our breakdowns of common 6.7 Cummins EGR problems and common 6.7 Cummins DPF problems show exactly where the factory setup struggles.
Upgrade #1: Emission Delete Kit
DPF regen interruptions eliminated under load
The number-one towing-and-MPG upgrade for the 6.7 Cummins is a complete emissions delete. The biggest towing payoff: once the DPF is gone and the truck is tuned for it, there are no forced regens — no mid-grade fuel dumps, no surprise exhaust-temp spikes while you're already working the truck hard. Regens also quietly hurt fuel economy every time they run, so eliminating them helps both towing reliability and MPG at the same time. A complete 6.7 Cummins delete kit bundles the hardware and tuning to do this as a one-time job.
EGR cooler failure prevented
The 6.7 Cummins EGR cooler is a known failure point — it can crack and leak coolant, and the EGR system fouls the intake with carbon over time. Deleting the EGR removes that failure risk entirely and stops feeding soot back into a clean intake, which matters most on a truck that tows hard and runs hot. If you want to scope just the EGR side, a dedicated 6.7 Cummins EGR delete kit covers it, though most tow owners do the full delete at once. For the complete decision framework, see our 6.7 Cummins delete kit buyer's guide.
Upgrade #2: Performance Tune
Adjusted fuel tables for tow loads
A delete is only half the job — the tune is what makes the truck run right and is where both towing reliability and MPG are won. A proper tune adjusts fuel tables, timing, and boost so the engine makes clean, efficient power under load instead of running hot and lazy. A quality 6.7 Cummins tuner is mandatory after a delete: the ECM has to be told the emissions hardware is gone, or you'll set codes and risk limp mode. Note the 6.7 Cummins ECM is locked on later trucks — our guide on 2019 Ram Cummins ECM unlock and tuning covers what that takes.
Custom tune vs pre-loaded delete tune
Most tuners ship with pre-loaded delete tunes that work great out of the box. For a dedicated tow rig, look for a tow tune in the stack — smoother power delivery, controlled EGTs, and fueling matched to heavy-trailer duty — rather than a single max-horsepower map. A custom-dyno tune can squeeze out a bit more, but for towing-and-MPG goals, a quality pre-loaded tow calibration is the sweet spot. Wondering whether tuning is even optional? Our guide on whether to tune when you delete settles it: yes, every time.
Upgrade #3: Lift Pump
FASS vs AirDog for Cummins
The Cummins runs a CP3/CP4 high-pressure injection system, and consistent fuel supply matters most under heavy load — exactly what towing creates. An aftermarket lift pump like a FASS or AirDog pulls fuel from the tank, separates air and water, filters it, and delivers a steady positive supply to the injection pump. Both FASS and AirDog are proven on the 6.7 Cummins; the choice usually comes down to filtration preference and flow rating for your power level. On a heavily-tuned or high-mileage tow build, a lift pump supports reliable fueling and adds filtration that protects the expensive high-pressure fuel system. It's a supporting upgrade, most valuable as power and towing demands climb.
Upgrade #4: Larger Exhaust
4" to 5" exhaust gains on Cummins
With the DPF gone, a free-flowing exhaust lets the Cummins breathe and sheds heat under load. The standard move is a 4-inch exhaust, with 5-inch favored on higher-output tow builds for even less backpressure and lower EGTs on long pulls. Lower backpressure means the engine works less for the same load — good for both towing temps and efficiency. Browse Cummins exhaust and diesel downpipes to match your build, and if you're going pipe-first instead of a full kit, a 6.7 Cummins delete pipe replaces the DPF section directly (still requires a tune).
Upgrade #5: Intercooler Upgrade
The intercooler (charge-air cooler) lowers intake air temperature after the turbo — cooler, denser air burns more efficiently. Under sustained towing, the factory intercooler can heat-soak, meaning it stops cooling effectively after prolonged high load, letting intake temps climb and costing you both power and efficiency on a long grade. An upgraded intercooler with more capacity keeps intake temps stable on the kind of extended pulls that heat-soak a stock unit. It's a supporting mod for serious heavy-tow builds rather than a first purchase.
Upgrade #6: Injectors
Stock vs 30% over for tow builds
For most towing-and-MPG goals, stock injectors are plenty — a delete and a good tow tune get you reliability and efficiency without touching fueling hardware. Stepping up to larger injectors (commonly 30% over) is a power-build decision: it supports higher horsepower and bigger fueling demands, but it's overkill for a truck whose main job is towing efficiently. If your goal is a reliable, fuel-conscious tow rig rather than a max-power build, leave the injectors stock and put your money into the delete, tune, and cooling upgrades first.
MPG Improvement Strategy
Delete + tune: real-world MPG gains
The biggest fuel-economy lever on a 6.7 Cummins is the same as the biggest reliability lever: delete + tune. Removing forced regens (each of which burns extra fuel) and running an efficiency-minded tune is where owners typically see the most meaningful real-world MPG improvement, both empty and towing. Results vary by driving style, weight, and tune, but the delete-plus-tune foundation is consistently the highest-impact MPG upgrade — which is exactly why it's also upgrade #1 on this list.
Aerodynamics and tire pressure
Don't overlook the free stuff. Towing MPG is heavily influenced by aerodynamics and tire pressure: keep tires aired to the correct load-rated pressure, avoid unnecessary drag (roof racks, oversized lifts, open tailgate myths aside), and drive smooth — steady throttle and reasonable highway speeds. These cost nothing and stack on top of the delete-and-tune gains. The fundamentals matter as much as the hardware when you're chasing every tenth of an MPG towing.
FAQ
What's the single best upgrade for 6.7 Cummins towing and MPG? A complete emissions delete with a proper tow tune. It eliminates forced regens, removes the EGR cooler failure risk, and is the highest-impact upgrade for both towing reliability and real-world fuel economy. A 6.7 Cummins delete kit plus tune is the foundation every other mod builds on.
Does deleting a 6.7 Cummins actually improve MPG? It's the most impactful MPG upgrade available, mainly by eliminating fuel-burning forced regens and allowing an efficiency-minded tune. Real-world gains vary with weight, driving style, and tune, but delete-plus-tune is consistently where owners see the biggest improvement.
Do I need a lift pump and bigger injectors just to tow? Not necessarily. For a towing-and-MPG focused build, the delete, tune, and exhaust come first. A lift pump (FASS or AirDog) is worth it on heavily-tuned or high-mileage trucks; larger 30%-over injectors are a power-build decision and usually overkill for an efficient tow rig — stock injectors are fine.
4-inch or 5-inch exhaust for a towing 6.7 Cummins? A 4-inch exhaust is the standard for most tow builds; 5-inch is favored on higher-output trucks for even lower backpressure and EGTs. Both reduce restriction after a DPF delete and help keep exhaust temps down on long pulls.
Is an emissions delete legal? For off-road/race use only. It is not legal for vehicles operated on public roads in the U.S. Check your state and local regulations before you buy.
→ Shop 6.7 Cummins Delete Kit
Ready to build a 6.7 Cummins that tows cooler, runs more reliably, and gives back MPG? Start with the upgrade that matters most: a complete 6.7 Cummins delete kit — an all-in-one solution with the hardware and tow tune to kill regens, drop EGTs, and remove the EGR failure risk for good. Pair it with a 6.7 Cummins tuner tow calibration and a free-flowing Cummins exhaust to finish the foundation.
