How Much Horsepower Does an L5P Have After Delete?

The 6.6L L5P Duramax — GM's current-generation diesel V8 introduced in 2017 — enters the performance conversation with a solid factory foundation. GM engineers this engine to deliver 90% of peak torque by 1,550 RPM.^[2] 445 crank horsepower and 910 lb-ft of torque^[1] are the numbers GM advertises, and they're legitimate. But crank horsepower and wheel horsepower are two different animals.

Run an L5P on a dyno in stock trim and you'll see 380–400 rear-wheel horsepower after parasitic losses through the heavy-duty Allison transmission and drivetrain. That's a meaningful gap — roughly 45–65 hp disappears between the engine and the pavement .

Understanding this baseline matters because every horsepower claim you'll read about delete kits references one of these two numbers. When someone says a delete adds 150 hp, they may mean crank hp. Nail down which measurement they're using before comparing figures. We always recommend referencing wheel horsepower for honest, apples-to-apples comparisons — it's what your truck actually puts to the ground.

Here's the honest breakdown of what a delete and tune actually delivers across tune levels. These aren't theoretical numbers — they reflect real dyno pulls and verified customer data .

One documented dyno pull recorded 594 rear-wheel horsepower and 1,281 lb-ft of torque on a max-effort tune, with adjustments made for elevation and wheel sizing . That's a beast of a number for a truck that left the factory making 380 hp at the wheels.

Torque is where the L5P delete story gets truly impressive. Diesel owners live by torque — it's what moves trailers, climbs grades, and makes the truck feel alive at low RPM. Here's what the numbers look like after a proper delete and tune.

• Street / Eco tune: +180 lb-ft, bringing total torque to approximately 1,090 lb-ft
• Performance tune: +240 lb-ft, pushing total torque to approximately 1,150 lb-ft
• Max-effort / race tune: +350 lb-ft or more, with documented pulls exceeding 1,260+ lb-ft at the wheels

These torque increases directly improve three things you'll feel every day: launch response from a stop, mid-range pull when merging or passing, and towing capability on grades and in headwinds. The low-RPM torque curve on a tuned L5P is where the real payoff lives — this engine was already a powerhouse in stock form, and tuning sharpens that curve dramatically. Most TDD customers running a performance tune report the truck feels like an entirely different animal under load.

Choosing the right package for your 2017–2023 L5P comes down to how you use the truck. Here's a practical breakdown by use case.

Daily driver / fuel economy focus: A street or eco tune paired with a full delete bundle delivers the best balance of power and fuel economy. Most owners picking this route report 3–5 mpg improvements at highway speeds — a real-world win on top of the performance gains .

Towing and hauling: A performance tune is the sweet spot. The +240 lb-ft torque gain means your truck handles grades and heavy trailers with noticeably less strain. Exhaust gas temperatures (EGTs) also run cooler post-delete because the engine breathes freely without DPF backpressure.

Competition / maximum power: A max-effort tune paired with supporting modifications is the path to 640+ hp. This setup is purpose-built for track use and requires upgraded supporting components to handle the added stress reliably.

Our GM/Chevy Duramax 6.6 L5P Full Delete Bundle covers the 2017–2023 model years and includes everything you need to get started.

Fuel economy improvement is one of the most consistent secondary benefits reported by L5P owners after a delete — and the mechanism is straightforward. The Diesel Particulate Filter (DPF) requires periodic regeneration cycles where the ECM injects extra fuel to burn off accumulated soot. Each regen cycle burns fuel without moving the truck forward. Eliminating that cycle alone recovers measurable MPG.

Real-world data from The Diesel Dudes delete kit testing shows tuned L5P trucks achieving 25 mpg at highway speeds on an eco tune, compared to the stock average of 22–23 mpg — a 2–3 mpg improvement on that tune level alone^[7] . Performance and max-effort tunes trade some of that economy for power, but still outperform stock on the highway when driven conservatively.

Beyond regen elimination, the delete also improves the air-to-fuel mixture by removing EGR (Exhaust Gas Recirculation) — the system that routes hot exhaust gases back into the intake. Cleaner intake charge means more efficient combustion. The result is a truck that's simultaneously more powerful and more fuel-efficient — a combination stock calibration simply can't match.

The delete and tune gets you most of the way there. But if you're chasing 600+ reliable wheel horsepower, supporting modifications close the gap. Here's what our technicians recommend in priority order:

1. Cold Air Intake: More airflow means more power. The S&B Cold Air Intake for the 2017–2023 L5P is a proven first step — expect a measurable boost in throttle response and EGT reduction at high load.
2. Upgraded Turbocharger: The factory VGT (Variable Geometry Turbocharger) has limits. A larger or upgraded turbo allows the engine to move more air at higher boost levels, which is where serious horsepower lives.
3. High-Pressure Fuel Pump (HPFP) Upgrade: At elevated power levels, the stock HPFP can become a bottleneck. An upgraded HPFP ensures consistent fuel pressure delivery under hard acceleration.
4. Injector Upgrades: Larger injectors support higher fueling demands at peak power. This modification is typically paired with a max-effort tune and turbo upgrade rather than a street setup.

According to The Diesel Dudes Technical Team, the most common mistake we see is customers chasing maximum tune power without addressing the fueling side first. Your tune is only as strong as the hardware supporting it.

Buckle up — this is where dyno numbers get nuanced. A deleted L5P producing 594 rear-wheel horsepower sounds incredible, and it is. But that figure comes with context that matters for setting realistic expectations.

Elevation: Air density drops roughly 3% per 1,000 feet of elevation gain. A truck tuned and dyno'd at 5,000 feet above sea level loses meaningful power versus sea-level testing. Documented dyno pulls account for this with elevation correction factors .

Wheel and tire diameter: Larger diameter tires affect how the dyno calculates wheel speed and, by extension, horsepower. A truck running 37-inch tires reads differently than one on 32-inch stock rubber — even with identical engine output.

Ambient temperature: Colder, denser air produces more power. Hot summer dyno pulls consistently read lower than cold-morning pulls on the same tune. Most reputable dyno operators publish SAE-corrected figures to normalize for these variables.

The practical takeaway: focus on before and after dyno comparisons on the same day and conditions, not absolute peak numbers from different setups. Your gains are real regardless of what the atmospheric conditions do to the peak figure.

Here's the full vehicle compatibility picture for the L5P delete ecosystem.

Standard pickup configurations — both crew cab and double cab — use a direct bolt-on exhaust delete pipe with no custom fabrication needed. Cab & Chassis trucks delivered without a bed require modified exhaust routing. Call us at (888) 830-2588 and we'll sort out exactly what your specific configuration needs before you order.