This 7.0L Duramax is built around one goal: diesel response that can hang in a monster truck. That starts on the exhaust side. If the cylinders do not scavenge cleanly, leftover exhaust contaminates the intake charge and limits cylinder fill no matter how much air you force in. That is why we start with our high-temp cast and ported Duramax race manifolds, large up-pipes, and a turbo system sized to move exhaust out as well as air in. From there, the super-turbo layout does two jobs. The supercharger gives us boost at idle and immediate hit off the line, which matters with a loose monster-truck converter. Then the twin turbos come on to carry the airflow and raise the overall pressure ratio. A bypass around the blower and a blow-off valve are there to manage that transition and keep the compressors out of trouble when airflow demand changes fast. The whole package is aimed at short, violent bursts of power with the response needed to chase a 1,300-horsepower target.
Gale Banks introduces the Banks Super-Turbo Diesel, a compound-boost Duramax build aimed at monster-truck use. The engine had previously been tested in Dyno Cell 1 with only a supercharger and zoomie-style exhaust, where it produced 666 horsepower. Banks was not satisfied with that result. Based on testing of the Monster Mud truck, he concluded that a competitive monster truck needs roughly 1,200 to 1,300 horsepower, so the objective became a diesel package with the immediate response of a blown 540-cubic-inch alcohol big-block Chevy while retaining diesel characteristics.
The next phase adds a pair of Precision turbochargers on top of the previously tested blower system. Banks describes the arrangement as "blowing the blower," meaning the turbochargers compress air upstream of the supercharger. The plumbing appears complex, but each tube and valve serves a specific purpose in managing airflow, temperature, pressure ratio, and transient response. The system is being assembled with the expectation that the engine will need both turbocharger control and supercharger bypass control once it returns to the dyno cell.
Banks emphasizes that high-performance diesel airflow is not only about forcing more air and fuel into the engine; it also depends on getting exhaust out efficiently. He frames this in terms of cylinder fill percentage, the percentage of intake-manifold air density that actually makes it into the cylinder. Poor exhaust scavenging leaves residual exhaust gas in the cylinder at the start of the intake stroke, which compromises the effectiveness of the compressor, intercooler, intake manifold, intake ports, and valve sizing. For that reason, the system begins with better exhaust flow: larger exhaust valves, improved exhaust ports, and a higher-flowing manifold or headers feeding the turbochargers.
The Banks high-temp cast and ported exhaust manifolds are substantially larger than stock. Banks notes that the stock Duramax exhaust ports are relatively small, while the Banks manifold is designed to fit 2001 through 2006 engines in that range, with a separate casting planned for the L5P. He also points out that the manifold port sizing will accommodate any commercially available cylinder-head port currently available. Outlet sizing is increased as well. The stock manifold outlet is about 1.75 inches in diameter, while the Banks manifold outlet is sized to support much larger tubing.
From the manifolds, the engine uses 2.5-inch stainless up pipes with 0.150-inch wall thickness, giving an inside diameter of about 2.200 inches, slightly larger than 2.208-inch nominal sizing. The bend radius is 3 inches. Banks contrasts this with the stock Duramax up pipe and says that even aftermarket up pipes are smaller than this setup. The goal is to minimize restriction on the hot side before the turbochargers.
Because exhaust gas temperature may reach around 1,600 degrees, Banks expects the stainless pipes to become somewhat flexible under heat. To control movement without making the system too rigid, the team machined collars to tie the two pipes together and added what he calls a compliance bend. That bend allows controlled movement so the system can expand and shift without fracturing. Additional bracing is planned from the pipe structure to the plate beneath the intercooler to further control motion in multiple directions.
The turbochargers are Precision 6870 ball-bearing units. Banks says they are sized to support the target power level while still delivering strong response. Each turbo uses a 2618 forged-aluminum compressor wheel and a 713C Inconel turbine wheel for high-temperature durability. The bearing system is dual ceramic ball bearing, chosen to improve transient response.
On the compressor side, the current configuration uses a 4-inch inlet and a 2.5-inch outlet. When the engine goes back into the dyno cell, Banks expects to feed the system with two large air filters and dual mass-air sensors into that 4-inch inlet to avoid pressure drop in the intake tract. He is also considering another compressor cover version, referred to as the H, with a 4-inch inlet and 3-inch outlet. To support either arrangement, the system already includes Banks-made diffuser hose connections that transition from 2.5 inches to 3 inches.
Compressed air leaves the turbochargers through 3-inch tubing and enters a water-cooled charge air cooler before flowing into the supercharger. Banks expects that once the turbochargers are fully active, the supercharger may need a bypass path around it. He is not treating that as a certainty, but he has built in the capability. A 60-millimeter Turbosmart wastegate is used as the bypass valve for this purpose. Because the bypassed air may exceed 400 degrees, an exhaust-style wastegate is appropriate due to its temperature tolerance.
The plan is to modulate that valve based on the pressure difference between the inlet and outlet of the blower. Air can then be routed around the supercharger and into the charge air cooler beneath it, or directed through the supercharger itself. Banks notes that the combined cross-sectional area of the bypass tubes and inlets exceeds the area of the 60-millimeter valve and seat, so the bypass path is not being choked by downstream plumbing.
A separate blow-off valve is mounted on top of the system. Although blow-off valves are commonly associated with gasoline turbo engines that have a throttle downstream of the compressor, Banks explains that a diesel can still encounter a similar surge condition. When fuel is cut after a hard run, engine rpm drops rapidly, and the compressors can momentarily have nowhere to send air. The condition is less pronounced than in a throttled gasoline engine, but still real enough to justify surge protection.
Banks takes time to distinguish between an intercooler and an aftercooler. He notes that many people casually call all charge air coolers intercoolers, but in this system the terminology matters. The smaller water-cooled unit placed between the turbochargers and the supercharger is an intercooler because it sits between one boosting device and another. The larger cooler downstream of the supercharger is an aftercooler because it is located after the final supercharging device. Both are charge air coolers, but they occupy different positions in the compression sequence and therefore serve different roles in the compound system.
On the turbine outlet side, the system uses 3-inch exhaust lines that quickly expand to 4 inches. Turbocharger boost control is handled by 45-millimeter exhaust wastegates with 45-millimeter outlets, which Banks equates roughly to 1.75-inch tubing. Those wastegates will likely dump toward the ground, while the main exhaust pipes are expected to exit through the roof of the monster truck. The sizing and routing reflect the short, violent duty cycle of monster-truck competition, where rapid response and minimal restriction matter more than long-duration steady-state operation.
Banks walks through how the compound system is expected to behave. At idle, the turbochargers are essentially loafing while the supercharger provides boost directly into the intake manifold. That boosted idle is important because monster trucks typically use very loose torque converters with stall speeds around 3,500 to 4,000 rpm. If the diesel uses the same type of converter common in blown Chevy-powered trucks, it may actually be too loose because the diesel should already be making boost and early torque before the turbos fully light.
The blower is expected to provide roughly 8 to 12 psi at idle and is considered effective up to about 22 psi. Beyond that point, Banks says it begins to hurt air density. He stresses that boost pressure by itself is not the real objective; boost is only the force that pushes air density from the intake manifold into the cylinder. What matters is the mass of air, expressed as pounds of air per cubic foot, that the engine can actually ingest.
As engine speed rises, the turbochargers begin to come on line. The initial turbine housing choice is a relatively tight 1.05 A/R to favor response. Banks acknowledges that the turbos may look somewhat small, but says the application is a response program with very short periods at wide-open throttle. Monster trucks spend only about 10 to 15 seconds at maximum load during events such as donuts, with the rest of the action consisting of repeated bursts. For that reason, fast spool and transient performance take priority.
Once fully active, the supercharger remains part of the pressure-ratio strategy, and the bypass system will determine how much compressor output goes around the blower and how much still passes through it. Banks says every super-turbo system they have built follows one of two basic arrangements: the first device to receive the air is considered "first." In this engine, it is turbos first. In other projects, including marine engines, a Pikes Peak 14-liter Detroit Diesel in Mike Ryan's Freightliner, and experimental Navy engines, Banks has also used blower-first arrangements where the blower feeds the turbos. The blower drive ratio is fixed relative to crankshaft speed, so the real tuning challenge lies in how the turbochargers and bypass strategy are managed around it.
The build remains an engineering experiment, but the target is clear: enough airflow, response, and compound-boost efficiency to reach the 1,300-horsepower range needed for a competitive diesel monster truck.