Understanding the 6.7 Cummins Platform

The Ram 2500 with the 6.7-liter Cummins turbo-diesel is a heavy-duty workhorse prized for its low-end torque and longevity. The engine features a cast-iron block, high-pressure common-rail fuel injection, and a variable-geometry turbocharger (VGT). While stock trucks deliver respectable fuel economy for their size — typically 15–20 MPG unloaded — the platform has significant untapped efficiency potential when modified carefully. Understanding the engine’s air, fuel, and exhaust systems is essential before selecting upgrades. Cummins has an official technical overview of the 6.7L available here.

Fuel Efficiency Modifications for 40+ MPG

Reaching 40 MPG in a three‑ton truck is an ambitious target — but with the right combination of airflow improvements, electronic tuning, and driving habits, gains of 50–100% over stock are possible. Each modification must work in harmony; mismatched parts can actually hurt mileage.

Cold Air Intake Systems

The factory air intake is designed for stock power levels and quiet operation, but it restricts airflow at higher boost levels. A high-flow cold air intake (CAI) pulls denser, cooler air from outside the engine bay, reducing inlet air temperature by 30–40°F. This improves combustion efficiency and allows the engine to burn fuel more completely. Look for filters with washable, high-flow media and heat-shield enclosures. Brands like BD Diesel and S&B Filters offer proven Ram 2500 CAI kits. Expect a 1–2 MPG gain under normal driving conditions, with additional benefits when towing.

Exhaust System Upgrades

Backpressure from the restrictive stock exhaust — especially the diesel particulate filter (DPF) and muffler — robs the engine of efficiency. A turbo-back or DPF-back exhaust system with a larger diameter (4 inches or more) reduces restriction. Deletion of the DPF is illegal on public roads in many regions, but a high-flow catalytic converter and straight-through muffler can help. For those in areas where emissions removal is not allowed, a performance exhaust with a free-flowing muffler still provides gains. Combined with a tune, an exhaust upgrade can add 2–4 MPG while lowering exhaust gas temperatures.

ECU Tuning and Fuel Mapping

Reprogramming the engine control unit (ECU) is the single most effective mod for fuel economy. Aftermarket tuners adjust fuel injection timing, pressure, and pulse width to match the upgraded intake and exhaust. Economy tunes lean out the air‑fuel ratio during light loads and stretch the injection window. Tuners like the Banks Power iDash DataMonster or the Edge Evolution CTS3 allow custom tuning profiles. A well-done economy tune can yield 5–10 MPG improvement, but always get a custom tune from a reputable shop — a generic off-the-shelf tune may damage the high‑pressure fuel system. Banks Power offers Ram-specific tuning with a focus on efficiency and towing reliability.

Turbocharger Optimization

The VGT turbo on the 6.7L is already efficient at lower speeds, but an upgraded turbo with larger compressor wheel and aero improvements can push the efficiency zone higher. A bigger turbo spools later but moves more air per pound of fuel — meaning the engine doesn’t have to inject extra fuel to reach a given boost pressure. For highway cruising, a turbo that maintains 8–12 PSI with low backpressure will improve MPG. Consider a drop‑in replacement like the BD Diesel S360 or the Fleece Performance Cheetah. However, turbo upgrades are most effective when paired with a tune.

Fuel System Upgrades

Stock fuel injectors and the CP4 high‑pressure fuel pump can deliver enough fuel for stock power, but if you are tuning for high MPG, you may not need larger injectors — in fact, oversized injectors can hurt atomization and reduce efficiency. The focus should be on fuel pressure stability and filtration. An aftermarket lift pump (e.g., from FASS or AirDog) ensures consistent fuel delivery to the CP4, preventing pressure drops that cause the engine to enrich the mixture. This alone can improve MPG by 1–2% and adds a safety margin for long‑distance towing.

Towing Efficiency Enhancements

Towing heavy loads — whether a fifth‑wheel camper, a gooseneck trailer, or equipment — magnifies every loss in the drivetrain. Improving towing efficiency means reducing aerodynamic drag, lowering rolling resistance, and maintaining stable vehicle dynamics. These mods also help the engine stay in its peak torque band, reducing fuel consumption per mile.

Suspension Mods: Airbags and Helper Springs

When the truck squats under load, the front-end lift reduces steering stability and increases aerodynamic drag (the truck acts like a plow). Installing air springs or helper springs, such as the Firestone Ride‑Rite or Timber Grove air assist kits, lets you level the truck while maintaining ride quality. At proper inflation (typically 30–60 PSI), the truck sits flat, the drivetrain angles stay correct, and wind resistance drops. This alone can improve towing MPG by 1–2 MPG.

Weight Distribution Hitches

For conventional tow trailers, a weight distribution hitch (WDH) uses spring bars to transfer some tongue weight back to the trailer axles and the front truck axle. This keeps the truck level, improves braking balance, and reduces rear‑end squat. The result is less drag and better traction in crosswinds. Brands like Equalizer and Blue Ox offer WDH systems rated for the Ram 2500’s high tongue weights. A properly adjusted WDH can improve towing MPG by 0.5–1 MPG by reducing rolling resistance from tire scrubbing.

Brake System Upgrades

Stopping a 30,000‑pound combined mass safely requires more than stock brakes. Upgrading to larger rotors, better pads, and a brake controller with proportional braking reduces brake fade and allows the driver to maintain higher average speeds (less need to slow down early). Power Stop’s Z36 kit with drilled and slotted rotors is a common choice. While brakes don’t directly add MPG, the ability to maintain momentum rather than constantly accelerating after a brake check can save fuel.

Transmission Cooling

The 68RFE or Aisin transmissions in the Ram 2500 run hot under load. High transmission fluid temperature indicates slippage and power loss. An aftermarket transmission cooler — such as the Derale 54,000 BTU unit or the Mishimoto with fan — keeps fluid temperatures below 200°F. Cooler fluid has better viscosity, reducing parasitic losses and improving efficiency. Expect a 0.5–1 MPG improvement on long grades. Always pair a transmission temp gauge with the cooler.

Performance Monitoring and Gauges

You cannot improve what you cannot measure. After making modifications, real‑time data helps you fine‑tune driving and detect problems before they cause damage. Essential gauges for the 6.7L include:

  • EGT (Exhaust Gas Temperature): Keep below 1,300°F under sustained load to prevent piston damage. A high EGT means the engine is running rich or the air flow is insufficient.
  • Boost Gauge: Monitors turbo performance. A slow spool or low max boost indicates a leak or restriction.
  • Transmission Temperature: Critical for towing. Stay under 230°F (210°F for extended periods).
  • Fuel Pressure: A drop below 40 PSI can starve the injection pump. Aftermarket lift pumps often display pressure.
  • OBD-II Scanner: Use a Bluetooth scanner with an app like Torque Pro to log instantaneous MPG in real‑time.

The Edge CTS3 Insight is a popular all‑in‑one monitor that shows these parameters on a color display. Monitoring your modifications ensures you stay within safe limits and can confirm MPG gains.

Combining Mods: A Balanced Approach

Reaching 40+ MPG is not about a single magic part — it’s a systems integration project. A typical build plan would proceed as follows:

  1. Install a cold air intake and a DPF‑back exhaust (or full turbo‑back if legal).
  2. Get a custom economy tune that matches the increased airflow.
  3. Add a lift pump for stable fuel pressure.
  4. Install airbags or helper springs for towing leveling.
  5. Add transmission cooling and monitoring gauges.
  6. Upgrade the turbo only if you tow heavy at altitude or want to push beyond 450 hp.

Each step must be tuned together; for example, a large turbo without a tune will spike EGTs. Work with a diesel performance shop that specializes in the 6.7L Cummins, such as BD Diesel or local tuners like Firepunk Diesel.

Real-World MPG Results and Driving Techniques

With the above modifications, many Ram 2500 owners report 25–30 MPG unloaded on the highway at 65 mph. A few hyper‑milers have crossed 40 MPG by using very light throttle, coasting when possible, and driving into a tailwind. However, a realistic goal for a daily driver with modest mods is 30 MPG unloaded and 12–15 MPG towing a 12,000‑lb load. To reach 40 MPG, you need:
- A custom tune with aggressive lean calibration
- Low rolling‑resistance tires (e.g., Michelin LTX) at high pressure
- Aerodynamic bed cover or tonneau
- Careful speed control (55–60 mph max)
- Elimination of all unnecessary weight

The Ram 2500 chassis itself is heavy, so every pound saved matters. Removing the rear seat and spare tire is common for competition builds, but for a work truck, focus on maintaining proper tire inflation and reducing electrical loads (e.g., unplugging block heater).

Final Considerations

Before beginning any modification, confirm local laws regarding emission components. DPF and EGR deletes are illegal in jurisdictions that follow EPA regulations and can result in fines or voided warranties. Look for CARB‑approved parts if you live in California or other states with strict smog laws. Also consider your transmission’s capacity — the 68RFE can handle about 650 lb‑ft of torque before requiring upgraded internals. With careful selection and professional tuning, the Ram 2500 with the 6.7L Cummins can become a remarkably efficient tow rig without sacrificing the durability that made the engine legendary.