So you want to build a 900 horsepower 6.7 Cummins. Not 500. Not 650. Not “it feels quick.”
We’re talking about a rowdy street truck that absolutely rips, and pulls like a freight train with an attitude problem.
Good news — the recipe is pretty simple.
Bad news — while it might be simple, it ain't cheap…
Here’s a simplified breakdown of what it takes to build a 900HP Cummins.
Step 1: 2nd Gen Swap w/ S472 Turbo (or Similar)
First things first — the stock turbo setup has to go.
A 2nd Gen swap moves the turbo to a more efficient, central location and opens the door for larger, more capable chargers.
A common choice for 900hp? S472 (or similar S400-frame turbo)
This gives you the airflow needed to support serious horsepower.
Bonus: it also sounds incredible.
Step 2: 100% Over Injectors + 12mm CP3 + FASS 165GPH Fuel System
Air is only half the equation. Now we need fuel.
This step is technically three upgrades, but we’re bundling it because....we can.
- 100% over injectors
- 12mm CP3 (or dual CP3 setup if you’re feeling spicy)
- FASS 165GPH Fuel System
More fuel + more air = better burnouts.
Step 3: ARP 625 Head Studs
At 900HP, cylinder pressure is no joke.
If you like your head gasket where it belongs, you’ll want:
ARP 625 head studs
This helps keep everything sealed when boost and cylinder pressures start getting aggressive.
Step 4: Pushrods + Valve Springs
Once you start pushing serious power, the valvetrain needs attention.
- Upgraded pushrods
- Heavy-duty valve springs
Again, technically two steps — but we’re still pretending this is simple.
This keeps everything stable at higher RPM and boost levels.
Step 5: Build the Transmission (Seriously)
Let’s be clear: Your stock transmission will not survive 900HP. Either on day one or a month from now, you will shred whatever stock transmission or clutch came with your Ram from the factory.
Your options:
- A fully built 68RFE
- A built Aisin
- A built clutch (for G56 trucks)
- Or go all-in with a 48 swap
Whatever route you choose — buy the best you can afford. Your trans is not the place to cut corners.
Step 6: Talk to Your Tuner (Ask for the Spicy Stuff)
Now it’s time to bring everything together. Contact your tuner of choice and let them know what you’ve built.
This is where calibration matters. The recipe given here will make between 750 and 900 wheel horsepower all day every day—depending on the truck, the dyno, the weather, and the tuning.
A good tuner will dial in:
- Fuel delivery
- Timing
- Boost control
- Drivability
And yes… this is where things get spicy. Tuning options like hard limiters and ultra-aggressive fueling are good for showing off, but can shorten the life of your engine.
What About Reliability?
A 900HP truck can be reliable — but it depends on:
- Build quality
- Tuning quality
- How you drive it
- How well you maintain it
This isn’t a “set it and forget it” build. Your 6.7 Cummins' stock bottom end will likely take 900hp very well—but constantly hammering on it will shorten your engine's life.
The Reality Check
We called this “6 easy steps.” In reality, it’s a serious investment of time, money, and planning.
But the result?
A 6.7 Cummins that makes 900 horsepower and absolutely dominates the street. The beauty of this power level is that it can be reliable and daily-drivable, while being absolutely nasty when you put your foot down.
Have questions? We're here to help.
- Phone: 636-429-7020
- Email: info@fassmotorsports.com
FASS Motorsports
25 Town and Country Drive
Washington, MO 63090
