A supercharged Duramax does not want the same camshaft timing a turbo diesel uses. Once engine speed climbs, the stock L5P cam simply does not keep the valves open high enough or long enough to support the airflow a blower-fed engine needs. That is why we developed the Banks Blower Cam for the L5P. The job is straightforward: increase valve lift and area under the curve so the engine can move more air, more times per minute, and carry power higher in the RPM range. But a blower cam cannot just add everything everywhere. Too much overlap wastes boost straight into the exhaust, and too much lift or timing in the wrong place risks valve-to-piston contact. So the design pushes exhaust blowdown earlier, adds meaningful lift and lobe area, keeps intake closing conservative enough for real street starting, and holds overlap in check. That is the balance. More airflow for a supercharged engine, without turning the exhaust into a pressure leak or the valvetrain into a piston-clearance problem. The result is a camshaft built for where this engine is headed: well beyond the stock power peak, with the airflow to support it.
Banks spent about a year developing a camshaft specifically for Lockjaw, its supercharged L5P Duramax project, because the diesel aftermarket offers many camshafts for turbocharged engines but essentially none designed around a supercharger. The result is intended to become a production Banks part sold as the Banks Blower Cam.
The engineering premise is straightforward: a supercharged diesel has very different airflow and exhaust-pressure conditions than a turbo diesel, so it should not automatically use the same cam timing strategy. The goal is not simply to add lift for its own sake, but to reshape the valve events so the engine can move more air at higher rpm while remaining compatible with the intended street-driven use of the vehicle.
Before measuring cam profiles, Gale points out that the L5P valvetrain differs from earlier Duramax engines. An earlier Duramax cam core has an oil groove in the fourth cam journal, a feature used to lubricate the turbocharger. That groove is absent on the L5P. According to Gale, GM changed the oiling strategy on the L5P, eliminating that journal-groove system and improving oil distribution elsewhere in the engine.
The lobe widths are also different. Earlier Duramax cam lobes are wider, while the L5P uses narrower lobes. Because of those dimensional differences, Banks plans to use a core made specifically for the L5P design when these blower cams and future turbo cams go into production. This is not just a regrind of an older blank; the later engine requires its own core geometry.
The narrower L5P lobes make more sense when viewed alongside the lifter design. Gale compares three roller tappets. The LML and earlier Duramax roller lifter weighs 202 grams, uses a 0.944-inch roller, and has a 1.790-inch body diameter. He describes it as extremely heavy. It uses a bushed roller rather than needle bearings.
The L5P roller tappet is much smaller and lighter at 137 grams. Its roller diameter is 0.700 inch, and the body diameter is 0.921 inch. The roller uses needle bearings, and Gale notes that the 0.700-inch roller diameter matches the Chevrolet LS valvetrain. In his view, GM effectively brought proven LS roller technology, used in millions of higher-rpm gasoline engines, into the diesel platform with a different body diameter.
He also shows a Jesel tappet weighing 95 grams, representative of a very high-rpm Pro Stock or Pro Mod style setup. That tappet uses a 0.850-inch roller and a 0.935-inch body. Based on those dimensions, Gale says an L5P could be machined by removing 0.014 inch from the lifter bore and adding a key groove to guide the keyed tappet, allowing the use of a lighter racing-style lifter.
At the cylinder head, the L5P uses four valves per cylinder with one rocker for the pair of intake valves and one rocker for the pair of exhaust valves. The intake and exhaust rockers have different ratios, so the cam lobes must be shaped differently to achieve the desired valve motion. Like many four-valve diesels with one rocker per valve pair, the engine uses a valve bridge. The rocker presses on the center of the bridge to open both valves together. That makes matched valve springs critical: both springs on a bridge must have the same seat pressure, spring rate, and open pressure. If one spring is weaker, one valve can lead the other, which becomes dangerous when piston-to-valve clearance is already tight.
Banks used a Cam Pro Plus system from Audie Technology in Norristown, Pennsylvania to characterize the camshaft. The machine uses a spherical follower and highly precise rotary and linear encoders to convert cam rotation into lift-versus-angle data. Gale emphasizes that the resolution is so fine that even footsteps near the machine can show up in the measurements.
The system measures base-circle runout, lobe lift, clearance ramps, valve lift at specified points, duration, area under the curve, lobe centerlines, lobe separation angle, valve overlap, and cylinder-to-cylinder phasing. Base-circle accuracy is measured to within five ten-thousandths of an inch. Lash and rocker ratio are entered so the software can calculate valve motion from the lobe profile.
Cylinder-to-cylinder phasing is especially important. In a V8 firing every 90 degrees, the valve events must also repeat correctly every 90 degrees. If the lobes are not phased properly, different cylinders can produce different power. That creates power imbalance, vibration, and crankshaft torsional stress that can eventually damage the crankshaft. The system also calculates tappet and valve acceleration and velocity.
Banks first measures the camshaft by itself, then compares that with measurements taken in the engine using encoders on the tappet and valve. Measuring in-engine captures the effects of the complete valvetrain, including rocker ratio, lash, valve spring load, and component deflection. Gale notes that valvetrain deflection can reduce actual valve lift by 0.010 to 0.015 inch, and the loss can be greater in a running engine than in a cold static measurement.
With the stock L5P cam, exhaust gross lift is 0.371 inch and intake gross lift is 0.385 inch. Gale walks through the four-stroke cycle to explain what matters in the cam plot. During the power stroke, peak cylinder pressure typically occurs roughly 8 to 16 degrees after top dead center, depending on load and other conditions. That is the only stroke that produces power at the crankshaft; the exhaust, intake, and compression strokes all consume power.
On the exhaust side, he focuses on the point where the exhaust valve begins to open, which he calls the blowdown intercept. By bottom dead center, the valve has reached a finite opening, and the area before bottom dead center represents the amount of exhaust blowdown that occurs before the piston starts back up the bore. Gale treats the area under the lift curve as a comparative indicator of mass airflow or mass exhaust flow.
He then overlays piston-to-valve clearance. As the piston approaches top dead center, the valves get close to the piston, so the vertical distance between the valve-lift trace and the piston-clearance trace indicates the available clearance. Banks is not cutting valve reliefs into the pistons because Gale does not want to disturb in-cylinder swirl and combustion quality. The objective is to determine how far the cam can be pushed while retaining flat-top pistons.
The stock cam has very little overlap, and what overlap exists occurs after top dead center. That leaves limited opportunity for incoming air to help scavenge residual exhaust. Gale notes that this may be acceptable for a stock engine that also uses exhaust gas recirculation, but residual exhaust still displaces oxygen in the cylinder. On the intake side, the valve remains open after bottom dead center to take advantage of intake-charge momentum. However, if the intake closes too late, air can reverse back into the port. Intake closing also affects cold starting because the engine must trap and compress enough cold air to generate the heat needed for ignition.
The central reason for a blower-specific cam is that a supercharged diesel does not face the same exhaust backpressure as a turbocharged one. In a turbo setup, exhaust pressure under load can exceed boost pressure; Gale gives an example of 40 psi boost with 50 psi exhaust pressure. That means the engine is pushing exhaust out against substantial resistance. With a pure supercharged diesel, there is no turbine section creating that restriction, so the engine exhausts against virtually no backpressure.
That changes the camshaft requirements. Lower exhaust backpressure reduces pumping losses, lowers exhaust gas temperature, and reduces heat rejection into the valves and pistons. Gale says the engine becomes easier on itself thermally, and piston cooling demand at a given horsepower is lower than with a turbocharged diesel.
Because the blower supplies boost without turbine restriction, the cam can be optimized to move more air through the engine rather than to cope with high exhaust pressure. At the same time, overlap must remain controlled. If both valves are open too long while the intake manifold is pressurized and the exhaust side has little backpressure, boost air can simply blow through the cylinder and into the exhaust manifold. Gale summarizes that as not wanting to supercharge the neighborhood; the goal is to supercharge the engine.
Banks produced two experimental grinds, the Banks 400 and Banks 500, named for gross valve lift. The Banks 400 is intended to work with the factory valve springs. Compared with stock, the exhaust valve opens earlier, moving the blowdown intercept significantly sooner. Gale says this is necessary because the supercharged engine is not being built for a 2,800-rpm power peak. The minimum intended operating point for peak power is around 3,800 rpm, so there is less time available for blowdown and exhaust evacuation.
The 400 grind also increases lift at bottom dead center, which raises exhaust flow as the piston starts up the bore. On the exhaust lobe, Banks reports a 26 percent increase in area. Gale is careful to say that this does not automatically mean 26 percent more flow, but it is a meaningful comparative increase in valve-event area.
Overlap is increased and advanced enough to become visible on the plot, but it is still kept modest. On the intake side, Banks adds 27 percent more area under the curve while keeping intake closing nearly unchanged. That conservative intake-closing strategy is deliberate because Gale wants reliable starting in cold weather. If the intake closes too late on a cold engine, there may not be enough compression heating to ignite the fuel cleanly. Since this is intended as a street setup that should run anywhere in the United States, Banks chose not to chase more high-rpm airflow at the expense of startability.
The Banks 500 raises both intake and exhaust gross lift to 0.500 inch and requires different valve springs. Relative to stock, it increases exhaust lobe area by 52 percent and intake lobe area by 54 percent. The exhaust valve opens even earlier, lift at bottom dead center is much greater, and the engine has already discharged a substantial amount of exhaust mass before the piston begins the exhaust stroke in earnest.
Despite the larger lift and area, overlap remains close to that of the 400 grind because Banks still does not want excessive blow-through from the pressurized intake side into the low-pressure exhaust side. Piston-to-valve clearance becomes much tighter than stock on both the 400 and 500 profiles. Gale stresses that these clearances are based on a balanced valvetrain with matched springs. Even then, the design must leave enough margin so that spring aging or unequal degradation over the life of the engine never allows the valves to contact the pistons.
Gale frames the entire cam program around airflow. The stock L5P can be spun faster with its factory camshaft, but horsepower falls off sharply because the engine runs out of airflow. The blower cam is meant to solve that by opening the valves farther and keeping them effectively open longer, increasing the area under the valve-motion curve and allowing more air through the engine at a given blower boost level.
The target is to move the power peak from the stock 2,800-rpm range up to roughly 3,800 to 4,200 rpm. Banks plans to drive the Whipple 3.8 supercharger at least four times crankshaft speed starting around 3,800 rpm if possible. The broader program is aimed at something that could eventually become a production-style supercharged crate engine.
Gale also hints at future headroom. He says Whipple is working on an even larger Gen 6 supercharger, and Banks' power goals are high enough that the larger unit may eventually be desirable. But regardless of blower size, the formula remains the same: more air, more times per minute. Higher valve lift and greater lobe area increase airflow, and higher engine speed increases the number of power impulses per minute. Together, those changes are what Banks expects to use to reach its supercharged diesel power targets.