This chassis had to do more than hold a big engine. It had to package a wide Duramax L5P, an Allison 1000, 5-inch exhaust, full suspension travel, and a ride height low enough to lay out without dragging hard parts. That meant getting the drivetrain as low as possible, which is why the dry-sump setup mattered. It also meant reinforcing the center section and rear structure for the kind of torque that breaks parts, not just the kind of horsepower that looks good on paper. A custom transmission mount keeps the package serviceable, and the Watts link keeps the axle centered through travel so tire clearance stays under control. The result is a chassis built around real packaging limits, real torque load, and real drivability.
The episode returns to Roadster Shop, where the LockJaw chassis is nearing completion. Josh, Mike, and Erik walk through the engineering changes required to package Banks' unusually large diesel drivetrain into the truck's custom chassis. The main challenge was not engine length, which is comparable to many V8 applications, but the drivetrain's overall width. Roadster Shop had to account for the engine, dry-sump system, steering path, motor mounts, and exhaust routing while still keeping the truck functional at full suspension drop.
Rather than redesigning the entire front structure from scratch, the team started with an existing front subframe from its spec platform and modified the geometry where necessary. The goal was to fit the engine as low as possible without creating interference problems. That low placement was especially important because the truck is intended to lay out dramatically, and the transmission oil pan still needed to remain just off the ground when the chassis is fully dropped.
To achieve the required engine height, Banks selected the shallowest available Allison transmission pan. Even with that choice, the engine oil pan remained a limiting factor, which is why the build moved to a dry-sump system. The dry sump allowed the engine package to be tucked higher into the chassis than would have been possible with a conventional wet-sump arrangement.
The resulting fit is extremely tight, but the major systems clear. The front sway bar fits without contacting the dry-sump pump, which had been a concern. The exhaust manifolds also ended up farther from the shock towers than expected. That spacing turned out to be beneficial because, with the selected tire diameter and the truck's ability to lay fully out, the manifolds stay clear of the upper control arm mounts. That should help prevent excessive heat exposure to the suspension bushings while still leaving a small but useful amount of clearance around the engine.
The transmission for the project is an ATS-built Allison 1000. Roadster Shop fabricated a custom tailshaft mount around the OEM transmission mount geometry using CAD data supplied by Banks. The mount was designed not only for strength, but also for serviceability. The transmission can be pulled back far enough to clear the torque converter and allow maintenance without forcing a major teardown of the truck.
Exhaust packaging was another major checkpoint. The chassis has been drawn to accommodate 5-inch exhaust, which had been a point of debate before the visit. The team was able to route that size successfully because the truck body is substantially wider than the frame rails, leaving useful packaging space outboard of the chassis. That extra width gave them room to preserve large exhaust routing without compromising the rest of the underbody layout.
Because this truck is expected to exceed 600 horsepower and produce substantial diesel torque, Roadster Shop strengthened areas that would normally remain simpler on its spec platform. On a typical short-bed truck chassis, the center section does not require extensive triangulation or reinforcement. In this case, however, the torque output changed the design priorities.
The team added a second series of center structure inside the chassis, bulkheaded by the transmission mount and reinforced with gussets and torque-boxed sections wherever possible. Additional gusseting was also added in the rear truss area, where the drivetrain's torque will ultimately be applied to the ground. The challenge was to increase stiffness and durability without sacrificing the suspension travel required by the air-ride setup.
Roadster Shop noted that it has experience with four-digit horsepower builds, including a 1965 C10 short-wheelbase truck on a Fast Track chassis that made 1,200 horsepower at the tires and roughly 980 lb-ft of torque with a manual transmission. Even so, this diesel combination required a different approach because of both the engine's weight and the way diesel torque is delivered. Those factors drove the decision to add reinforcement in places that might not be necessary on a gasoline-powered build.
At the rear, the chassis uses a Watts link rather than a traditional Panhard bar. Mike explained that with the amount of suspension travel required by a bagged setup, a single lateral link would force the axle to move sideways through its arc as the suspension compresses and extends. That lateral shift becomes a serious packaging problem when the build is trying to maximize wheel and tire fitment while also achieving an extreme ride-height range.
A Watts link keeps the axle centerline aligned with the truck centerline throughout suspension travel. It also fixes the roll center at the center pivot of the Watts mechanism, so the roll center remains consistent as the truck moves through its range of motion. That gives the system both packaging and handling advantages. Roadster Shop described this geometry as part of its in-house proprietary system, developed through years of experience and used across its C10 and truck spec slam chassis. The use of heim joints adds further adjustability, allowing the rear suspension to be fine-tuned more precisely.
The team also reviewed how Roadster Shop models suspension movement during development. A separate front suspension module is built in CAD as a complete independent front suspension assembly, with its own articulation points. That allows each side to be moved independently so the engineers can study what happens on the actual truck, then return to the digital assembly and revise the design as needed.
This process helps verify clearances at full compression, full drop, and steering lock. It also illustrates how carefully the truck has been packaged: the chassis can be adjusted to bottom out simply by changing shock length in the model because the rest of the assembly relationships are already defined. The discussion makes clear that the truck's stance and suspension travel were not improvised visually; they were engineered through repeated digital checks before fabrication.
Wheel and tire sizing turned out to be one of the most important factors in making the truck lay out correctly. The rear combination was chosen specifically to avoid the tire protruding through the top of the bed when the suspension is fully collapsed. Roadster Shop settled on a 295/30R24 rear tire, which measures 31 inches in diameter. That size puts the tire right at the upper limit of what the bed will tolerate when the truck is aired out.
The front uses a 22-inch wheel rather than a 24 because the front package needed both a smaller overall diameter and a narrower section width. Those constraints were necessary to preserve steering articulation from lock to lock. With a 24-inch front wheel, the truck would have had very poor turning radius because the tire would be tucked too far into the body and suspension structure, even at ride height.
The front package also had to clear the inner hood seam and the upper fender-well structure when the truck drops. Without that clearance, the aired-out position could force the tire into the bodywork and require a complete rethink of the front fender and core-support structure, potentially pushing the build toward a tubular front-end solution. Roadster Shop's objective was to preserve usable steering angle at ride height while still allowing the truck to achieve the desired slammed stance.
Aside from the drivetrain width, the front of the chassis did not require a complete departure from Roadster Shop's established 1960-1966 truck knowledge. The company relied on what it already knows works on these trucks and adapted that catalog of geometry and fitment data to this specific build. Even so, the interaction between wheel and tire fitment, track width, and the way the engine cradles over the front suspension made this front-end package highly specific to LockJaw.
The discussion also touched on body details that may need revision once the truck is assembled. With the rocker line and rear bumper position shown in the model, the bumper appears to dip into the ground when the truck is fully laid out. That may require either raising the bumper with revised mounts or removing it altogether, depending on the final visual direction of the build.
The last major unknown is the supercharger and intercooler stack height. Roadster Shop has CAD for the blower, but at this stage the exact hood relationship is still difficult to judge because of the complexity of the surface models. What is already clear is that the drivetrain has been placed as low as physically possible while still keeping the transmission pan off the ground. Lowering the engine any further would create serious safety and clearance problems.
That means the hood line will have to adapt to the powertrain, not the other way around. Banks noted that the newer Whipple 3.8 is slimmer than the 5.0, which may help, but the intercooler beneath it is still substantial. The current cooler is about 7 inches tall, and the combination is expected to run around 30 psi of boost. Earlier testing with the super-turbo setup had shown 7 psi at idle when overdrive was at 200 percent, and after reducing overdrive to 33 percent, boost climbed into the low-30-psi range.
The conclusion was straightforward: the blower will likely break the hood plane, and if it does, the hood will simply need an opening. With the engine already at its lowest viable position, that is the unavoidable outcome of the chosen induction package. The episode closes with the promise that the next visit will move from CAD review to the real chassis downstairs, where the team will inspect the actual Banks chassis in production.