You could argue that the 4th Gen Cummins is one of the best diesel performance platforms ever.
The legendary 6.7 Cummins. Endless aftermarket support. Tons of fueling options. Countless VGT, compound turbo, and 2nd Gen swap turbo setups available.
And, this is a big one, no ECM encryption. The computer used in the 4th Gen Cummins doesn't require a special unlock of any kind.
So what does it take to build a 900 horsepower 4th Gen Cummins?
Here’s a simple breakdown of the major parts you need to build a 900HP 4th Gen Cummins.
Built Transmission
If you want 900 reliable horsepower, you're going to spend money on your transmission.
For most 4th Gen Cummins owners, that means one of three options:
The 68RFE gets picked on a lot, but a properly built 68 can absolutely work in a serious street truck when it’s built by the right people and matched with the right tuning.
The Aisin is known for being tougher in stock form, but definitely needs attention at this power level.
And if you’re one of the G56 manual guys, the clutch becomes a major part of the build. At 900HP, a stock-style clutch is not even in the conversation.
100% Over Injectors
A set of 100% over injectors is a common choice for this kind of build because they provide the additional fuel volume needed to support serious power.
Cheap injectors, mismatched injectors, or poorly calibrated injectors can make the truck smoke more, run worse, tune harder, and generally act like it hates you.
Even at 900+hp, a quality set of 100% over injectors can be tuned to drive great and be reasonably efficient.
12mm CP3
With 100% overs, you'll need more high-pressure fuel supply.
That’s where a 12mm CP3 comes in.
The CP3 is one of the most proven high-pressure fuel pumps in the diesel world, and a 12mm pump is perfect for street driven, high-horsepower Cummins builds.
For a 900HP truck, you need a 12mm stroker pump will make sure those injectors flow all the fuel your tuning commands.
FASS 165GPH Fuel System
Before the CP3 can do its job, it needs a steady supply of clean, consistent fuel.
That’s where the FASS 165GPH Fuel System comes in.
At this power level, fuel supply is not something you want to gamble on.
A FASS 165GPH System helps provide:
- Higher fuel volume
- Improved filtration
- Air and vapor separation
- Consistent supply to the injection pump
- Better protection for expensive fuel system components
When you’re running 100% over injectors and a 12mm CP3, a FASS Fuel System is not just an accessory.
It’s part of the foundation.
ARP 625 Head Studs
Cylinder pressure is a real thing.
At 900HP, the factory head bolts are no longer what you want holding everything together.
ARP 625 Head Studs are one of the most common upgrades for serious 6.7 Cummins builds because they help keep the cylinder head clamped down under high boost and high cylinder pressure.
Can people make power on lesser hardware? Sure.
Should you cut corners on head studs when you’re trying to build a reliable 900HP truck? Nope.
Pushrods
Pushrods are one of those upgrades that don’t sound very exciting until you understand what they’re doing.
At higher horsepower and cylinder pressure, the valvetrain sees more stress.
Upgraded pushrods help reduce flex and keep the valvetrain more stable.
That means better control, better consistency, and less chance of the stock parts becoming a weak point.
They’re not flashy, but they matter.
Valve Springs
Valve springs are another must-have at this level. As boost, drive pressure, RPM, and overall cylinder pressure increase, the valvetrain needs more control.
Upgraded valve springs help prevent valve float and keep everything behaving the way it should.
That becomes especially important when you’re asking the engine to make serious power and still survive.
Custom Tuning
This is where the whole package comes together.
Custom tuning is absolutely critical on a 900HP 4th Gen Cummins build.
The tuner needs to account for:
- Injector size
- CP3 output
- Turbo setup
- Transmission setup
- Desired power level
- How the truck will actually be used
A good tuner can make a 900hp 4th Gen Cummins have great street manners, while being an absolute animal under heavy throttle.
Please note: Due to federal laws, we do not offer, install, or recommend custom tuning. Please consult with an independent tuning company for more information.
What About the Turbo Setup?
We didn’t list one specific turbo setup here because there are a lot of ways to get to 900HP.
S400-based 2nd Gen Swaps are extremely popular at this power level. However, compound turbo setups definitely have their place too.
The right turbo setup depends heavily on your goals for the truck overall.
A daily driven street truck that tows a lot might be better off with compounds. A dedicated show truck or weekend cruiser might be more fun with a 2nd Gen Swap.
Don’t Forget the Supporting Details
A 900HP truck also needs the "small stuff".
That can include:
- Intake and intercooler piping
- Charge air cooling
- Gauges and monitoring
- Driveshaft and U-joint inspection
- Traction bars
- Proper tires
- Regular maintenance
The bigger the power number, the more the small details matter.
A truck that makes 900HP once is cool. A truck that can do it every day is even cooler.
Is 900HP Streetable?
For sure! But expectations matter.
A well-built 900HP 4th Gen Cummins can daily driven, but it is not going to feel like a stock truck. It may be louder, smokier, laggier, firmer, more sensitive to maintenance, and much harder on parts.
The "Basic" 900HP 4th Gen Cummins Parts List
Here’s the simple version:
- Built 68RFE, built Aisin, or 900HP-capable G56 clutch
- 100% over injectors
- 12mm CP3
- ARP 625 head studs
- Upgraded pushrods
- Upgraded valve springs
- FASS 165GPH Fuel System
- Custom tuning
- Correct turbo setup for your goals
- Supporting airflow, cooling, drivetrain, and monitoring upgrades
That’s the foundation.
From there, the exact build depends on the truck, budget, usage, and how wild you want to get.
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
