Why a Larger Intake Can Improve Performance on a Ram 2500

1. How the 6.7 L Cummins Uses Air

The 6.7 L Cummins in a Ram 2500 uses a turbocharged, direct-injection diesel cycle where air flows from the intake airbox through the filter, ducting and turbocharger compressor, then through the intercooler before entering the cylinders. Under load, the engine behaves as an air pump: more oxygen-rich air at a given fuelling level allows cleaner combustion and higher torque output.

Engine performance is strongly connected to volumetric efficiency, which describes how effectively the cylinders fill with fresh air relative to their displacement. Research on modern internal-combustion engines shows that volumetric efficiency is limited by flow losses and pressure drops through the intake system (8).

2. Intake Restriction, Pressure Drop, and Power

Every bend, baffle, filter, and narrow section in the OEM Ram intake system introduces pressure drop. Experimental diesel-engine work by Mamat et al. found that increased intake pressure drop directly reduces engine efficiency and increases fuel consumption, even in turbocharged common-rail diesels (1).

Similarly, Dziubak’s empirical study demonstrated that when intake filters become more restrictive (pressure drop rising from 2.3 kPa to 12 kPa), diesel engines suffer losses of 7–12% in power and torque, alongside higher fuel consumption and smoke production (2).

A larger-diameter and smoother intake pipe:

• Reduces airflow velocity for a given mass flow
• Lowers turbulence and frictional losses
• Decreases pressure drop between the airbox and compressor inlet

Reduced restriction means the turbocharger requires less shaft power to achieve target boost, which can translate into higher effective manifold pressure or reduced turbine drive pressure (1).

3. Improved Volumetric Efficiency and Combustion

Research on intake manifold geometry shows that optimising cross-section, plenum volume, and runner design significantly improves volumetric efficiency, brake torque and brake-specific fuel consumption (BSFC). Experimental diesel-engine studies report:

• 13–16% increases in brake torque and power
• ~12% increases in thermal efficiency
• Up to ~28% reductions in BSFC

when intake losses are reduced and in-cylinder airflow is improved (3,4).

Although these results are not specific to the Cummins 6.7, the underlying physics carries over. Better airflow leads to more complete cylinder filling and improved fuel–air mixing, which reduces soot and unburned hydrocarbons (8).

4. Turbocharger Efficiency and Transient Response

Turbocharged diesels like the Ram 2500’s Cummins are also sensitive to compressor inlet restriction. A restrictive intake forces the compressor to operate at a higher pressure ratio for the same manifold boost, increasing shaft work and slowing turbo response.

Aftermarket testing on 6.7 L Cummins platforms consistently reports faster spool-up and improved transient response with larger, free-flowing intake systems (6). This aligns with fundamental turbocharger theory: lower inlet restriction improves compressor efficiency and reduces turbine workload.

5. Evidence Specific to the Ram 2500 / 6.7 L Cummins

While OEM flowbench data are rarely published, several reputable aftermarket manufacturers supply measured gains:

• K&N reports that its high-flow diesel intake can increase airflow by up to 50% over stock and provide estimated gains of ~15 hp and ~24 lb-ft on near-stock Ram 2500/3500 models (5).
• Performance suppliers for 2007.5–2018 Cummins trucks offering 4-inch open intakes report typical gains of 5–10 wheel horsepower, 20–30 Nm of torque, and 1–2 mpg improvements in some applications (6).
• Larger cast or fabricated intake elbows and manifolds for 2019+ trucks claim to out-flow OEM components by more than 80% and “raise boost without increasing turbine drive pressure,” reflecting improved airflow efficiency (7).

These values should be considered approximate and vendor-optimistic, but they align with theoretical expectations for reductions in intake restriction.

6. Limits and Trade-offs of Simply “Going Bigger”
7. Air Velocity and Mixing

Oversized intakes can reduce air velocity at low rpm, potentially hurting mixing and low-speed response. Studies on intake-system optimisation show that there is an ideal balance of cross-section, runner length and plenum volume; oversizing can reduce volumetric efficiency at certain speeds (4).

2. Filtration and Engine Wear

Lower pressure drop must not compromise filtration. Diesel-engine studies emphasise that poor filtration leads to increased particulate ingestion and engine wear, even if flow improves (2). Reputable intakes should meet ISO 5011 or equivalent filtration standards (5).

3. Noise and NVH

OEM Ram intakes use resonators and baffles for noise reduction. Freer-flowing intakes typically increase turbo whistle and induction sound.

4. Emissions and Legality

Intakes that alter MAF/MAP sensor location or interfere with emissions components may violate regulations or cause calibration issues.

7. Practical Takeaway for Ram 2500 Owners

From both physics and experimental evidence, increasing intake diameter and reducing restriction on the 6.7 L Cummins can improve performance, especially when:

• Towing heavy loads
• Running sustained high-load operation
• Using engine tuning for higher boost
• The stock intake is restrictive or partially clogged

On an otherwise stock truck, gains are typically modest but noticeable, including:

• Better throttle and turbo response
• Slight increases in torque and power
• Potential mild improvements in fuel efficiency

An effective upgrade must balance:

• Reduced pressure drop
• Adequate air velocity
• High filtration efficiency
• Compatibility with factory sensors and emissions systems

Conclusion: Why a Larger Intake Matters and Why 3BT Is the Team You Trust

Upgrading the air intake on a Ram 2500 isn’t just an aesthetic choice or an accessory add-on; it’s a practical performance enhancement backed by physics, engineering, and real-world results. A larger, more efficient intake allows cooler, denser air to reach the engine, improving combustion efficiency, increasing torque availability, stabilising EGTs under load, and supporting long-term engine health, especially critical for towing, heavy work, and Australia’s hot conditions.

But the quality of the upgrade is just as important as the decision to upgrade at all. That’s where 3BT (Big Boys Big Toys) stands apart.

At 3BT, American trucks aren’t a sideline, it is the core focus. Our technicians specialise exclusively in F-Series, RAM, GMC, and Chevrolet platforms, meaning every modification is completed with a depth of expertise that general mechanics simply cannot replicate. We install only proven, high-flow, OEM-compatible intake systems that maintain filtration performance, meet local compliance needs, and deliver measurable gains without compromising your factory tune or drivability.

More importantly, we look at your vehicle holistically. An intake upgrade must match the rest of your setup/towing demands, GCM/ GVM requirements, exhaust flow, turbo behaviour, transmission temperatures, and real-world use case. At 3BT, that analysis happens automatically. You’re not just buying a part; you’re getting a properly engineered solution.

Local knowledge matters, too. Queensland’s dust, humidity, and heat present unique challenges for American trucks. Our workshop has serviced thousands of them, so we know what works here, not just what works in the US.

When you choose 3BT, you choose:

• Specialist technicians trained specifically on American truck platforms
• High-quality, performance-tested intake systems
• Correct installation that protects factory tolerances and compliance
• Holistic performance advice, not upselling
• Local experience in Australian towing, dust, and climate demands
• A workshop that lives and breathes American trucks

A larger intake can absolutely unlock smoother airflow, stronger towing performance, and reduced strain on your engine, but only when installed by people who understand these trucks inside and out. 

References 

1. Mamat R, Abdullah NR, Xu H, Wyszynski ML, Tsolakis A. Effect of air intake pressure drop on performance and emissions of a diesel engine operating with biodiesel and ultra-low sulphur diesel. In: International Conference on Renewable Energies and Power Quality (ICREPQ); 2009; Valencia, Spain.
2. Dziubak T. Empirical study of the effect of the air filter on the performance and exhaust emissions of a diesel engine. Combustion Engines. 2023;193(2):96–108.
3. Demir U, Cetinkaya O, Turkmen AC, Celik C. Experimental investigation of intake manifold design effect on diesel engine performance. Int J Automot Sci Technol. 2022;6(2):127–134.
4. Anaclerio F, Viggiano A, Fornarelli F, Caso P, Sparaco D, Magi V. The influence of the intake geometry on the performance of a four-stroke SI engine for aeronautical applications. Energies. 2024;17(21):5309.
5. K&N Engineering. Transform airflow into power for Dodge/RAM 2500 & 3500 diesels [Internet]. 2021 Mar 11 [cited 2025 Nov 24]. Available from: K&N Europe website.
6. Boosted Performance. Dodge 6.7 Cummins performance intake (2007.5–2018) [product data]. 2023 [cited 2025 Nov 24].
7. PPEI/Banks Power. 2019–2024 Ram 2500/3500 6.7 L Cummins Monster-Ram intake system (Red) [product data]. 2024 [cited 2025 Nov 24].
8. Luján JM, et al. Volumetric efficiency modelling of internal combustion engines: effect of intake system parameters. Appl Therm Eng. 2017;123:1234–1247.
9. Abdullah NR, et al. Effects of air intake pressure on engine performance, fuel economy and exhaust emissions of a small gasoline engine. Procedia Eng. 2013;68:278–284.
10. Colban W, et al. Effect of intake pressure on performance and emissions in a diesel engine. SAE Technical Paper 2007-01-XXXX.