Ram 2500 6.7 Cummins compound turbo build Houston Drop Forged Diesel
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Ram 2500 · 6.7 Cummins  ·  Houston, TX

RAM 2500
CUMMINS
COMPOUND BUILD

The S300/S400 compound turbo build is the most-requested Stage 3+ path on the 6.7 Cummins. Here's how we build it, what it requires, and what it realistically produces.

500+RWHP Potential
1,000+LB-FT Torque
4Prerequisite Systems
Why Compound Turbos

A SINGLE TURBO
CAN'T DO WHAT
TWO CAN.

A large single turbo on a 6.7 Cummins makes big peak power numbers — but it spools late and produces a power curve that's narrow at the top and hollow in the mid-range where towing and daily driving actually live. A compound setup changes that completely.

A small secondary turbo (the inner, or "secondary" in Cummins compound terminology) spools immediately and builds boost in the low-RPM range where the engine is most responsive. A large primary turbo takes over as RPM climbs, producing high-volume airflow at the top of the power band. The result is power that's usable across the entire RPM range — not just on a dyno sheet.

The compound build requires doing the fuel system correctly first — FASS lift pump and CP3 conversion for 2019+ trucks. The turbo sizing has to match the fuel delivery capability. The transmission needs to be built before a high-output EFI Live tune goes on. We plan all four systems at the consultation.

S300 S400 compound turbo kit Cummins 6.7 Houston
Compound Build — What's Involved
FULL BUILD SCOPE
  • FASS 150 or FASS 220 lift pump — fuel delivery foundation
  • CP3 injection pump conversion (2019+ 6.7 Cummins only)
  • S300 secondary + S400 primary compound turbo kit
  • Intercooler upgrade — larger core, high-flow end tanks
  • 68RFE or Aisin transmission build — compound torque requires it
  • EFI Live Stage 3 compound tune — calibrated on dyno
Turbo Configurations

S300/S400 Compound Configurations on the 6.7 Cummins

Compound sizing depends on the power target, use case, and whether the truck needs to also tow or compete. We size the combination at the consultation — bigger isn't always better for street and tow applications.

Street / Tow Compound
S300 + S400
STAGE 3 STREET
Primary: S400 — 75mm inducer, 1.00 A/R
Secondary: S300 — 62–64mm inducer, fast spool
Power range: 500–650 rwhp / 900–1,100 lb-ft
Best for: Street, daily driving, towing — broad power band, strong low-end. Most requested configuration.
Trans requirement: 68RFE or Aisin build
Most Common
High-Output Street / Competition
S300 + S480
STAGE 3+ HIGH OUTPUT
Primary: S480 — 80mm inducer, 1.10 A/R
Secondary: S300 — 64mm inducer, fast spool response
Power range: 650–800 rwhp / 1,000–1,200+ lb-ft
Best for: High-output street, tow competition. Big top-end with secondary covering low-RPM.
Trans requirement: Full Aisin or 68RFE build required
Competition / Sled Pull
S366 + S480
COMPETITION
Primary: S480 — 80mm inducer, 1.32 A/R
Secondary: S366 — 66mm inducer
Power range: 800–1,000+ rwhp depending on fueling
Best for: Sled pull and high-competition builds. Requires full drivetrain plan.
Trans requirement: Full built Aisin with trans brake
Before the Turbos Go In

Prerequisites That Can't Be Skipped

The most common mistake on compound builds is installing the turbos first and figuring out the supporting systems later. That sequence produces damaged injection systems, failed transmissions, and poorly calibrated engines. These are done first — before the turbo kit gets ordered.

01
LIFT PUMP — FASS 150 OR 220

The compound turbo build demands injection pump fuel supply that a stock lift pump cannot sustain. The FASS 150 is standard for Stage 3 street builds. High-output compound builds (S480 primary) get the FASS 220. Lift pump first — injection pump second — compound turbos third. Non-negotiable sequence.

02
CP3 INJECTION PUMP (2019+ ONLY)

The 2019+ 6.7 Cummins uses a CP4 injection pump from the factory. The CP4 cannot sustain the injection rail pressure demand of a Stage 3 compound build — catastrophic pump failure is the outcome, not a possibility. CP3 conversion is completed before any compound turbo work begins on a 2019+ truck. 2013–2018 trucks are already CP3 — no conversion needed.

03
INTERCOOLER UPGRADE

A compound turbo setup produces significantly more compressed air volume than a stock single turbo. The stock intercooler core cannot cool that air mass effectively — inlet temperatures rise, detonation risk increases, and power ceiling drops. A larger-core intercooler with high-flow end tanks is part of the compound build package, not an optional add-on.

04
TRANSMISSION BUILD

A compound 6.7 Cummins produces 900–1,200 lb-ft of torque at the crank. The stock 68RFE torque converter and clutch pack were calibrated for 450 lb-ft. A Stage 3 compound build without a built transmission produces a broken transmission within a few hundred miles. The 68RFE or Aisin gets built before the tune goes on. See the transmission upgrades page for what a built 68RFE or Aisin involves.

The Calibration

EFI LIVE
STAGE 3
COMPOUND TUNE.

The compound tune is not a Stage 2 tune with the fueling tables turned up. The compound turbo system has different boost characteristics, different EGT behavior, and different charge air temperature curves than a single turbo. The calibration has to be written for the specific compound configuration installed — primary and secondary sizes, intercooler core, and fuel delivery capacity all inform the tune.

We calibrate on EFI Live, verify power output and EGT curve on the chassis dyno, and deliver a multi-file tune (street, tow, and economy profiles where applicable). The street and tow profiles are separate calibrations — not the same fueling table with different shift points.

For the full platform context, see the Ram 2500/3500 Cummins page which covers Stage 1 through Stage 3 in the context of the full platform build path.

EFI Live Stage 3 compound tune Cummins 6.7 Houston
Compound Build FAQ

Ram 2500 Compound Turbo Questions

What we're asked most about the S300/S400 compound Cummins build.

What does a compound turbo Cummins feel like compared to a single turbo?+
The most noticeable difference is the power curve breadth. A large single turbo produces strong peak power but with a narrow band and a turbo lag valley below 1,500 RPM. A properly configured compound setup has power available from idle — the secondary turbo is small enough to spool immediately, and the primary takes over before the secondary runs out of flow. The result is a truck that pulls hard in the 1,200–1,800 RPM range where you actually tow and drive, not just above 2,200 RPM where a big single finally comes on.
Is the CP3 conversion required on all Ram 2500 compound builds?+
Only on 2019 and newer 6.7 Cummins trucks. The 2013–2018 Ram 2500/3500 6.7 Cummins uses a CP3 injection pump from the factory — no conversion needed. The 2019+ model years switched to a CP4 pump as part of a fuel system redesign. The CP4 cannot sustain Stage 3 compound fueling demand, so a CP3 conversion is a required prerequisite on those model years before compound turbo installation. We confirm pump type at the consultation.
What transmission is best for a compound Cummins build?+
The Aisin AS69RC is the stronger starting point for compound builds — it's rated for higher torque stock and requires less extensive modification to handle compound power levels. The 68RFE can be built to handle it, but requires converter upgrade, servo pressure increase, clutch pack upgrade, and a recalibration that goes beyond what the Aisin needs. If you're ordering a new truck with a compound build in mind, we recommend speccing the Aisin. If you already have a 68RFE, we build those for compound duty regularly — it's more work but it's done.
Can a compound Cummins still tow reliably after the build?+
Yes — and the towing performance is noticeably better than a stock or Stage 1/2 truck when done correctly. The compound setup's low-RPM torque advantage directly benefits towing: the truck pulls loaded grades without the RPM surges a single turbo produces under load. The tow tune profile is calibrated specifically for sustained load — EGT management, boost targets, and fueling rate are all adjusted for the towing duty cycle. Stage 3 compound trucks are regularly used as daily tow rigs.
How long does a full compound build take?+
A complete compound build — FASS lift pump, CP3 conversion (if needed), compound turbo kit, intercooler upgrade, transmission build, and EFI Live compound tune — typically takes four to six weeks depending on parts lead times and shop schedule. We place all parts orders after the consultation and before the truck comes in, so the build moves efficiently once started. Planning the build three to six months before you need the truck on a job or at an event is the right approach.
Ram 2500 Cummins compound build Houston Drop Forged Diesel
Plan Your Compound Build

READY TO BUILD
THE COMPOUND?

Bring the model year, current mods, and the power target. We'll scope the full build — fuel system, turbos, trans, and tune — from the consultation forward.

BOOK YOUR CONSULTATION
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