The diesel horsepower war has officially entered a weird, and honestly pretty surprising new chapter.
For years, the Cummins guys have had the easiest argument in the room:
- Who makes the biggest power? Cummins.
- Who holds the records? Cummins.
- Who dominates the extreme horsepower diesel world? Yep, still Cummins.
That part is not really up for debate. When you start talking about the absolute highest horsepower diesel trucks on earth, the Cummins platform is still the king.
Buuut, there is a different conversation happening now.
And that is:
If you want the most power with the least amount of hard parts, the modern 6.7 Powerstroke and L5P Duramax are the tune-only kings right now.
The New Diesel Horsepower War
Over the last few years, tuning support for the newer L5P Duramax and modern 6.7 Powerstroke platforms has opened up in a major way.
For a while, these trucks were locked down. The engines were strong, the fuel systems were capable, the turbochargers had potential, you just couldn't tune the darn things.
Once the aftermarket started making real progress with unlocking and tuning these trucks, everything changed.
Suddenly, lightly modified trucks were putting down numbers that used to require a WAY longer parts list.
What Do We Mean by “Tune-Only”?
When people say “tune-only,” they usually do not mean the truck is literally untouched.
Most of the time, they mean the truck still has most of the factory hard parts in place, such as:
- Factory injection system
- Factory high-pressure fuel pump
- Factory turbocharger
- Factory long block
- Factory transmission in many cases
There may still be supporting upgrades, especially airflow-related parts, maintenance items, monitoring, or drivetrain improvements.
But, you're not talking about a built engine, S400 turbo, big injectors, or anything of the sort
You're talking about a mostly stock truck with tuning and a few smart supporting modifications making a seriously impressive number.
Why the L5P Duramax Is So Impressive
The L5P Duramax changed the game.
Compared to earlier Duramax platforms, the L5P brought a stronger foundation, improved fueling capability, and a factory setup that responds extremely well once tuning enters the conversation.
The stock fuel system, stock turbo, and factory engine have proven they can support excellent rear-wheel horsepower numbers with very little hard-part modification.
Depending on the dyno, weather, correction factor, truck setup, and who is doing the tuning, these trucks are often talked about in the 590 to 610+ rear-wheel horsepower range with tuning and airflow-style upgrades.
That's wild for a modern heavy-duty diesel truck with almost no physical mods.
Why the 6.7 Powerstroke Is Right There With It
Ford’s modern 6.7 Powerstroke is a monster with good tuning.
The newer 6.7 Powerstroke trucks have strong factory fuel systems, capable turbos, and engines that have shown they can make huge usable power without needing a giant list of aftermarket parts.
Just like the L5P, modern 6.7 Powerstroke trucks can live in that same general 590 to 610+ rear-wheel horsepower conversation with tuning and a few key hard parts.
Again, the exact number depends on the dyno, the weather, the correction factor, the truck, the tune, and the setup.
Why the 2024 and Older 6.7 Cummins Aren't Quite There
This is where the Cummins crowd gets mad. And we get it—we love Cummins around here.
The 6.7 Cummins is an incredible engine (duh). It's simple, it has a massive aftermarket, and it is still the engine you want when the goal big horsepower.
But in the modern tune-only conversation, the 2024 and older 6.7 Cummins isn't quite on the same level as the newer L5P Duramax and 6.7 Powerstroke.
Throw an S472 and some 100% over injectors on a Cummins and you've got a party—but that's not the point of this article.
What About the 2025+ Cummins?
The 2025+ Cummins can't be tuned quite yet. That will likely change soon—and when it does, it may steal the tune-only crown.
It probably will eventually.
But right now, if someone wants a new or lightly used diesel truck, very minimal modifications, and roughly 600 horsepower on tap, the L5P Duramax and 6.7 Powerstroke are the two platforms everyone is watching.
The Bottom Line
The diesel horsepower war is alive and well.
The Cummins platform still owns the top of the mountain when it comes to all-out horsepower records.
But, in the tune-only world, the L5P Duramax and 6.7 Powerstroke are leading the charge.
With factory fuel systems, factory turbos, and factory engines capable of supporting tire-shredding power, these trucks have become the go-to choice for owners who want big power with minimal hard-part modification.
Have questions? We're here to help.
- Phone: 636-429-7020
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Email: info@fassmotorsports.com
FASS Motorsports
25 Town and Country Drive
Washington, MO 63090
