555 Horsepower isn't the Full Story

What's the first number you look at when a new heavy-duty diesel drops? Horsepower, right? Maybe torque? Yeah, that's where everybody's eyes go, but Gale Banks looks somewhere else. After you see why, you won't go back.

General Motors just reignited the heavy-duty diesel horsepower war with its all-new 8.3-liter Duramax L6P, codenamed "Mongoose." This V8 makes 555 horsepower and 1,230 lb-ft of torque. Big numbers, sure, but the one Gale cares about is horsepower per liter.

See what's coming for the new Duramax 8.3L.

Why Horsepower Per Liter Matters

Here's how we use it: specific output tells you how hard an engine is being asked to work. Picture two guys carrying the same load up a hill. One is a big fella walking it up, and the other is a smaller guy sprinting flat out. They both get there, but you know which one is going to be sucking wind! Same idea inside an engine.
The L6P makes 66.9 hp/L. The outgoing 6.6L L5P makes 71.2 hp/L. Ford's 6.7L Power Stroke, at 500 horsepower, works at 74.6 hp/L.

That lower number is no accident. GM engineers told TFL Truck that adding displacement let them dial back specific output, which lowers combustion and exhaust-gas temperatures and helps hold down NOx. So GM didn't just build a bigger engine to make more power. They built one that makes more power while working less hard for it. 

That gives the L6P room to grow. If GM wants more horsepower down the road, there's plenty of headroom before it reaches the Power Stroke's level of effort.

It also hands Ford a benchmark. Take Ford's 74.6 hp/L and apply it to an 8.0-liter engine and you get about 597 horsepower… essentially 600 hp. If Ford answers the L6P with a bigger Power Stroke, this war could get loud in a hurry.

Material Science Meets Big-Cube Diesel Power

Now for the bones. The L6P starts with a compacted-graphite-iron (CGI) block. Think of CGI as gray iron that's been hitting the gym: substantially stronger, so engineers can control weight and still handle the crushing cylinder pressures a diesel makes.

We know this stuff firsthand. More than two decades ago, we used a CGI block in a military-related marine program and in the development of the 5.9L Cummins-powered Banks Sidewinder Dakota that made 735 horsepower, an astonishing 118.6 hp/L, while being engineered to survive brutal durability requirements. So yes, we're a little biased about CGI!

GM backed the block with a serious bottom end: a fully forged crankshaft, forged-steel connecting rods and steel pistons.

Those steel pistons are the interesting part. Unlike aluminum, steel doesn't conduct heat as readily, so the piston crown and combustion bowl can take a lot more thermal abuse. The catch is that all that heat has to go somewhere, and it has to be pulled out aggressively. GM handles it with electronically controlled piston-cooling jets and a variable-displacement, gear-driven oil pump that ramps up cooling flow under heavy load and eases off to save parasitic losses when you're cruising.

Gale calls this combination a "marriage made in heaven": CGI structure underneath, steel pistons on top.
A Bigger Turbo Without Bigger Numbers… Yet

The L6P also gets a much larger turbocharger. GM has confirmed it's a high-efficiency variable-geometry unit, but hasn't told us the inducer or exducer sizes, so we don't yet know how much bigger the compressor and turbine wheels really are.

What we can tell from the engine's architecture is that this turbo was designed to move a lot more air than the L5P's. And it's paired with a new two-stage water-to-air charge-air cooling system.

Why does that matter? Because making boost is only half the game. Think of a charge-air cooler as a radiator for air. The first-stage "knockdown" cooler yanks heat out of the compressor discharge right away, and a second water-to-air cooler finishes the job before the air reaches the intake manifold. The path is shorter and more compact, too, which means less volume to fill and a quicker response when you stand on the pedal.
For a truck that has to drag enormous loads up long grades, keeping things cool matters every bit as much as peak airflow.

Torque at Diesel RPM

The L6P hits its 1,230 lb-ft peak at just 1,400 rpm, and it stays above 1,200 lb-ft across a broad chunk of the operating range. Rated horsepower arrives at 2,500 rpm, which is 300 rpm sooner than the L5P's 2,800 rpm peak.

That low-speed muscle fits GM's whole strategy. The engine doesn't have to scream to make its numbers. It gets them from displacement, airflow and cylinder pressure at relatively lazy engine speeds. The result is a motor built around what heavy-duty work really demands: massive low-rpm torque, thermal control that doesn't quit, and structural strength.

And that's the most interesting thing about the L6P. Looks to me like GM didn't just build a bigger Duramax. They built a platform with more displacement, lower specific output, and plenty of thermal and structural headroom.

For Ford, the math is already on the wall. If the next Power Stroke grows in displacement while holding its current specific output, 600 horsepower stops being a milestone and becomes a simple calculation.

The diesel horsepower war is back, folks. This time it's being fought with materials, airflow and combustion temperature just as much as with horsepower.

Banks Is Building for the Mongoose

We have big things in store for the new 8.3L. Here's what's coming and why each piece matters.

Getting the Air In

Ram-Air Intake: A bigger turbo breathes harder, and a stock airbox is built for dust collection, not performance. Our Ram-Air intake pairs a massive, low-restriction filter with a big induction tube, and our patented Air Mass Control Module and Crankcase Ventilation Control Module lets us build an intake far bigger than the stock sensor setup would normally allow. 

Monster-Ram: Ever felt a truck "cough" under load and blame the road? That can be turbo surge, which Gale Banks calls "silent surge," because you can feel it more than you hear it. Our Monster-Ram is being engineered for smooth, surge-free airflow, and its larger outlet and organic shape raise air density at the compressor, so shaft speeds drop and the engine reaches its target boost sooner. Translation: sharper throttle response, no surge, and a happier turbo. With a compressor as big as the Mongoose's to feed, that matters even more.

Boost Tube Upgrades: Factory charge-air plumbing leans heavily on small-diameter pipes and rubber hose. Our mandrel-bent tubes are larger, smoother and stronger, and billet venturi-style couplers help hold boost pressure and airflow. Think of it as swapping a garden hose for a fire hose. The more air the Mongoose's turbo pushes, the more those pipes matter.

Getting the Exhaust Out

Monster Exhaust: Air that goes in has to come out, and a stock DPF-back system is a bottleneck. Our large 5" diameter system with the patented SideKick tip cuts backpressure and lowers exhaust exit temperatures. It aims exhaust gas out the side of the truck instead of blasting regen heat straight at your trailer. Less backpressure means the turbo spins easier, and an engine that breathes out freely runs cooler. And, thanks to GM's tightened electronic tolerances, reducing backpressure in the exhaust system results in a check engine light... unless you're Banks. Our patented Exhaust Pressure Control Module module currently included in the Monster Exhaust System allows us to reduce backpressure after the DPF without setting codes. 

Keeping Everything Cool

Remember those steel pistons? GM had to build serious cooling around them, because heat that doesn't leave the engine stays in the oil. And oil that runs hot wears out faster. That's why the next upgrades are all about pulling heat out of every fluid on the truck.

CoolRunner Oil Pan: Built with technology from our military engine program, the CoolRunner will add extra oil capacity and far more cooling surface area than a stock pan. Our FlowThru Fins move heat out through the pan, and unlike stock, it lets every last drop drain during an oil change.

Ram-Air Differential Cover: Our patented Ram-Air scoop design forces air across the housing and cools five times better than flat-back covers, all while keeping the same ground clearance as factory. With 1,230 lb-ft going to the rear axle, cooler gear oil is cheap insurance.

Ram-Air Transmission Pan: Same idea, different fluid. Our pan will add extra fluid capacity and far more cooling surface area than stock, plus a breakaway scoop that protects the pan if you hit something. Cooler fluid means a longer-lasting transmission.

Water-to-Air Intercooler Upgrade: GM went water-to-air on the L6P, and so are we. We're designing it to eliminate airflow restrictions and increase boost air density. Everything about the Banks Intercooler for the 8.3L Duramax is bigger. Improving airflow lowers boost loss which increases air density and oxygen content of the air entering the engine. That amplifies power, lowers exhaust gas temperatures (EGTs) and improves fuel economy pull after pull after pull.

Power and Information

Derringer Tuner: Our tuner for the L6P will be warranty friendly, with no reflash required and no trace left after removal. Six power levels can be changed on the fly, and our AutoRate and ActiveSafety circuitry watches the engine and transmission for you. More power, and the engine stays protected… period.

PedalMonster: The Mongoose makes its 1,230 lb-ft peak at just 1,400 rpm, but you won't feel it through a lazy accelerator pedal, and waiting on a response doesn't help you merge, pass, or pull away from a light. Factory throttle tuning holds the pedal back, and PedalMonster fixes that with smooth multi-point torque curves for better take-off, stronger mid-range punch, and a predictable pedal feel.

It's the only torque response controller that talks to the engine control module in real time, in both directions, reading your speed, gear, and powertrain data so its adjustments are tailored to your truck at that moment.

High-Torque, Mid-Range, and High-Performance modes each offer 10 sensitivity levels, controlled through your iDash or the mobile app. Banks ActiveSafety returns the truck to stock torque delivery if it detects a fault, Reverse Safety restores stock throttle response when you're backing up, and the whole system is warranty friendly and leaves no footprint after removal.

iDash Data Pro: A brand-new engine means nobody knows what "normal" looks like yet, so let's find out. The iDash unlocks data the factory dash never shows, and it can record up to 100 parameters at once. It also controls the Derringer and PedalMonster. You'll see what's happening under the hood before you ever feel it.
New engine. Same Banks playbook: breathe in, breathe out, stay cool, and know exactly what's going on.

See what's coming for the new Duramax 8.3L.

Beating an L6P with Your L5P

It's worth noting that Duramax owners have the option to add Banks upgrades to beat the L6P's rated horsepower. For example, assuming a 10% drivetrain loss, the L6P will put 499.5 hp to the ground. A Banks Derringer tuner-equipped 2020-23 Duramax will make 523 at the rear wheels, and a Derringer-equipped 2024-26 Duramax will put down 519 hp to the ground. And that’s just one of the Banks performance parts already available.

If the L6P's power and torque is appealing but the price tag of a new truck isn't, adding a Banks to your L5P is a cost-effective, engine-safe and warranty-safe solution.