We start with a complete 6.6L Duramax engine as shipped, then strip away the stock front drive, intake, EGR, turbo outlet hardware, and other systems that don’t belong in a supercharged package. The point isn’t just to bolt on a blower. A diesel responds to airflow, so the whole engine has to be built around moving more air cleanly and keeping the valvetrain stable while doing it. That’s why this Banks R866SC gets a proprietary Comp cam, matching valve springs, Trend pushrods, a custom Banks Fluidampr and crank pulley, larger injectors, and a modular two-piece intake manifold with an integrated charge-air cooler. On top sits a 3.8-liter billet supercharger driven hard enough to put the blower in its working range without overspeeding the engine. We also keep an eye on what actually fails and what doesn’t. That’s why some factory hardware stays when it proves it can do the job. The result is a Duramax that’s engineered as a system, not a pile of parts. More airflow, better control of cylinder pressure, and cleaner tuning all matter if you want a blown diesel to live.
The build begins with a 2021 Duramax engine in "engine as shipped" form, meaning it arrived essentially as GM sends it from the Duramax assembly plant to the truck assembly plant. These engines are complete enough to serve as a useful starting point, but much of the factory hardware is removed for the LockJaw project. Similar engines are also being used in other development work, including monster-truck engine programs, camshaft development, and the broader Killing a Duramax series.
On the front of the 2021 engine, one immediately noticeable change from earlier Duramax layouts is the dual belt-plane arrangement. The rear belt plane is the conventional accessory drive, while an additional pulley system bolted to the vibration damper, along with its own pulley and tensioner, drives only the engine fan. GM added this to increase cooling and oil-cooling capacity, supporting towing loads up to 36,000 pounds. Even so, for this project nearly everything on the front of the engine is discarded: the thermostat assembly and duct casting, accessory mounts for the air conditioning compressor and alternator, the fan-drive hardware, and even the stock vibration damper.
The stock intake hardware is also stripped away. Gale points out the factory intake manifold casting, nicknamed the "sad giraffe" because of its shape, and notes that it goes straight to the scrap pile. The associated EGR plumbing and control hardware are removed as well.
At the rear of the engine, the turbocharger's variable-geometry mechanism is visible along with the compressor outlet, EGR cooler, control valves, and the exhaust path leading into the first emissions device. The catalytic converter bolts directly to the back of the turbocharger, followed by the downpipe. All of that is removed for this racing-oriented build.
Gale makes a distinction between legal emissions compliance for street applications and what is appropriate for a dedicated racing engine. This engine will run without emissions equipment, including no DPF, but he emphasizes that it still must be tuned cleanly so it does not smoke. His goal is to calibrate it to a nominal Euro 3 cleanliness level, an older standard that can still produce a substantially cleaner-running engine without relying on modern aftertreatment, provided the tuning and airflow strategy are correct. That strategy becomes clearer once the intake manifold and supercharger system are installed.
Attention then shifts to the supercharger drive system. A blower pulley was machined onto the outside diameter of the damper assembly, but the team quickly decided it was not large enough. The replacement pulley is dramatically larger, to the point that Gale jokes it resembles an old Raider Mag wheel. Despite the humor, the sizing is deliberate: the lower pulley diameter relative to the small upper blower pulley establishes the overdrive ratio needed to spin the supercharger fast enough.
The stock L5P drive plane is about 10 percent smaller in diameter than the stock vibration-damper setup being replaced. The assembly also incorporates a timing wheel. L5P engines normally use a rear trigger, but Gale prefers moving the trigger to the front when using one of Banks' crankshafts. That allows a full counterweight at the rear of the crank instead of machining the rear counterweight to carry a timing wheel. He acknowledges there are arguments for both front and rear trigger locations, but if the crankshaft is strong enough and vibration levels remain acceptable, he is comfortable with the front-trigger arrangement. A custom piece positions the stock sensor correctly, although that particular setup will not be used on this engine.
The damper itself is finished in a new Banks Red Cerakote color intended for introduction at the 2021 SEMA show. Gale notes that the shade includes a bit of gold flake to warm the color compared with earlier versions of Banks Red.
A major internal change is the second-generation blower camshaft. Gale had previously developed a first diesel-specific blower cam with roughly 0.400-inch nominal lift that worked with stock valve springs and stock valve gear. That cam improved airflow and power, but he wanted more. Working again with Billy Godbold at COMP, the team went through multiple iterations and completed a full cam-development program before arriving at the new design.
The new camshaft increases nominal lift from 0.400 inch to 0.500 inch. That additional lift created a problem with the stock valve springs, which would coil-bind and bend pushrods. To solve that, a new valve spring was developed that preserves OEM-style packaging. It uses the correct top and bottom diameters, fits with the factory seal and spring-alignment hardware, and retains the factory retainer and keeper assembly. Gale specifically wants this kind of OEM-compatible solution because he is trying to create components that could, in principle, be installed on the assembly line while still carrying factory-style design cues. The new spring also supports higher engine speed and improves overall valvetrain stability.
Pushrod development was handled with Trend. The engine uses larger-diameter, thicker-wall pushrods with a one-piece construction so the lifter engagement is formed from the tube rather than being a separate inserted piece. A rocker-arm ball cup is pressed into the top. These pushrods have already been tested on the dyno, and Gale describes them as excellent. As with the valve springs, he is also thinking about what a factory-assembly-compatible version might look like.
Because changing the camshaft requires removing the front cover, pulling the heads, and extracting the lifters, the original torque-to-yield head bolts are discarded. They are one-time-use fasteners and are not reused. What is notable is what goes back into the engine: stock GM head bolts.
Gale explains that in Banks' Duramax programs, including L5P builds making well over 1,000 horsepower, they continue to use stock head bolts rather than switching automatically to studs. Although a stud arrangement can provide greater clamping force, he questions whether that makes it inherently superior or even necessary. In his view, studs are not justified until there is an actual head-gasket failure problem to solve, and he says they have not had head-gasket issues on these engines at those power levels.
His reasoning is based on how the system behaves under firing pressure. The head bolts thread into the block deck, and combustion pressure tries to lift the cylinder head slightly. The head gasket has some spring-back capability, allowing it to follow that movement. Gale prefers to preserve that compliance. He argues that the stock bolt system provides some cushioning in the threads, whereas a more rigid stud arrangement can transfer shock loads more directly into the block. He has seen blocks crack around the head-bolt threads in the deck and says that when he sees that kind of failure, he wants to know whether the engine was running stock bolts or studs. His point is not that studs never work, but that making the system more rigid can simply move the failure point elsewhere.
The same philosophy applies to the bolt retaining the vibration damper. Banks continues to use the non-reusable GM bolt. This engine will be an especially severe test because the supercharger drive places substantial cantilevered load on the front of the crankshaft.
Balance is therefore critical. The team already knows the damper assembly itself is balanced and properly doweled, but they still want to verify the large pulley assembly. In principle, a CNC-machined part should be very close, but Gale still wants it checked on the balance machine and zero-balanced if necessary.
The oversized lower pulley and tiny upper blower pulley are central to the drive strategy. The ratio is simply the lower diameter divided by the upper diameter, and the target is roughly 4:1. They want the blower turning at least 16,000 to 16,500 rpm, but Gale believes it really starts to come into its own around 18,000 rpm. The supercharger can operate well above 20,000 rpm. At the same time, he does not want to spin the engine much beyond about 4,400 rpm. That combination of engine-speed limit and desired blower speed is what drives the extreme pulley sizing. With the new springs and increased cam lift, the team expects the valvetrain to remain stable in that operating range.
The intake manifold is one of the centerpiece components of the build. It is a two-piece design intended to support more than one induction strategy. In one configuration, it accepts an integrated charge-air cooler inside the manifold with a blower mounted on top. In another, it can take an inlet casting on top and support a turbo or compound-turbo arrangement.
Gale describes the integrated cooler as the final stage of charge-air cooling. In a compound-turbo setup, there would be an intercooler between the first and second compressor stages, followed by this aftercooler in the manifold. He notes that all of these are charge-air coolers; the terminology simply reflects where they sit in the system. The manifold's modularity is intentional, allowing the same basic architecture to support future development paths.
The version shown here is the first one machined from billet. The lid, being fabricated separately by Mike Thermos of Nitrous Supply in Huntington Beach, California, will include additional provisions. During assembly, the manifold is lowered carefully into place using alignment dowels, one of which comes from the stock setup. Once seated, it establishes a very different top-end layout from the original engine-as-shipped configuration.
By the time the top-end hardware is installed, the engine differs radically from the stock shipped engine. It now carries a custom Banks Fluidampr, a custom crank pulley, the new blower camshaft, Trend high-performance pushrods, Banks valve springs, and the custom two-piece intake manifold with integrated charge-air cooling. On top sits a 3.8-liter billet supercharger with a dual inlet. The engine is also configured for nitrous use, fitted with custom injectors rated at 50 percent over, and equipped with extremely aggressive headers.
Even at this stage, the fuel system may evolve further. Gale notes that the S&S injectors could eventually become 100 percent over, especially once nitrous is added. He also explains that on other projects they eventually reach the limit of the stock Denso pump. With additional lift-pump pressure, these systems can do more work. The stock upper limit is around 60 PSI lift pressure, but Banks has found that pushing that into the 70 to 80 PSI range under high demand, using a pressure-modulated or regulated strategy tied to engine load, can extend capability. Ultimately, however, the preferred solution is an S&S-converted Bosch pump to replace the stock unit. Whether this engine will need that upgrade remains to be seen.
The immediate plan is to install the engine in the truck, fire it there, and then take it to SEMA before moving to dyno testing. With SEMA only days away, the schedule is tight, but the first phase of the LockJaw Duramax combination is now clearly defined: a heavily reworked L5P built around airflow, charge density, valvetrain control, and a supercharger system sized to deliver serious boost without sacrificing mechanical stability.