At 852 horsepower and 3,300 rpm, this L5P is already running well past the stock engine’s natural horsepower peak. That means the stock camshaft has become a restriction. The real issue is airflow timing: at higher rpm, there’s less time to get exhaust out and fresh charge in, so pumping losses go up and cylinder fill starts to fall off. This new COMP Cams Duramax Stage 1 camshaft is aimed right at that problem. Lift only increases slightly so it stays within stock valve spring limits, but duration increases substantially on both intake and exhaust. That gives the exhaust more time to blow down and the intake more time to fill the cylinder without pushing valve events so far that compression heat suffers. In plain terms, it’s a camshaft built to move the L5P’s useful power higher in the rpm range. That matters because the goal isn’t just a different idle or a bigger parts list. It’s to carry horsepower from the stock peak up toward 3,800 rpm, reduce exhaust-side pumping restriction, and help this Duramax make the jump from 852 hp to the 900 hp range with the rest of the airflow package.
The video opens as an unboxing of a newly released Comp Cams Duramax camshaft, which Banks says is the first one they have received. The shipment arrives in two boxes rather than one, with the first box containing promotional items from Comp Cams rather than engine parts. Those extras include decals, black T-shirts, three large banners measuring roughly 3 feet by 8 feet, shop aprons, and fender covers intended to protect painted bodywork while working under the hood. After acknowledging the swag and setting it aside, the focus shifts to the actual camshaft.
Banks frames the camshaft as an often-overlooked upgrade in diesel performance builds. Many Duramax owners pursue compound turbocharging and other airflow modifications, but never address the camshaft itself or the pistons. In this case, the camshaft was ordered specifically for the ongoing Killing a Duramax project, where the current L5P combination recently produced 852 horsepower at 3,300 rpm.
That operating point is significant because the stock L5P engine makes peak horsepower at about 2,800 rpm. Running the engine 500 rpm beyond its natural horsepower peak suggests that the stock camshaft has become a limiting factor. Banks describes the engine as essentially being out of camshaft at that speed, meaning the valve events are no longer well suited to the higher-rpm airflow demand.
The broader plan is to reduce exhaust-side pumping restriction so the engine can move spent gases out of the cylinders more efficiently. Banks explains that improving flow from the exhaust ports in the heads, through the up-pipes, into the turbocharger, and then out through the exhaust system reduces pumping losses. That frees parasitic horsepower otherwise consumed pushing exhaust through restrictions.
With less exhaust trapped in the cylinder, the engine should achieve a higher percentage of cylinder fill at the same manifold air density. Based on that change, Banks expects the combination to move from 852 horsepower to roughly 900 horsepower. He also previews supporting hardware already under development, including all-new up-pipes, turbo mounting, air intake components, and a full 5-inch exhaust system. The goal is to reach 900 horsepower while still using the same turbocharger.
The camshaft itself is described as a billet part, meaning it is machined from a single solid piece of bar stock rather than cast. Comp Cams starts with round 5160 steel stock and machines away everything that does not belong in the final camshaft shape. Banks checks the grind number on the rear of the cam and identifies it as 130-300-13.
He then outlines the manufacturing process. The camshaft is rough-machined first, then induction-hardened to 60 on the Rockwell C scale, and finally finish-ground to its completed form. The result is a hardened billet cam intended for durability and precise lobe geometry.
One of the notable features of this grind is its intended fitment range. Banks says the camshaft is capable of fitting Duramax engines from 2001 through 2020. He explains that this was not assumed; it was confirmed through recent back-and-forth work between Banks and Comp Cams, including review of available grinds and direct measurements inside an L5P engine.
That fitment work focused on two critical mechanical limits. First, the valve lift had to remain low enough to avoid piston-to-valve contact. Second, the lift also had to stay within the limits of the stock valve springs so the springs would not coil bind. This particular camshaft is therefore designed as a stock-valve-spring-compatible grind rather than a more aggressive setup requiring upgraded springs.
Banks briefly explains the camshaft's role for viewers who may not be familiar with valvetrain operation. The camshaft opens the valves to let intake air into the cylinder and to let exhaust gases out. In this Duramax application, the lobes act on roller cam followers, or tappets, which move pushrods. The pushrods then actuate rocker arms, and the rocker arms open the valves.
He notes that a more detailed explanation will appear in a future Killing a Duramax episode, but the key point here is that camshaft shape determines how far the valves open, how long they stay open, and when those events occur relative to piston motion. Those factors strongly influence airflow, cylinder filling, exhaust scavenging, and the rpm range where the engine makes power.
Banks compares the stock L5P camshaft profile with the new Comp Cams Stage 1 stock-valve-spring grind using a graph. On the stock cam, represented by the blue trace, maximum intake valve lift is 0.375 inch and maximum exhaust valve lift is 0.380 inch. Duration at 0.050 inch valve lift is 155 degrees on the intake side and 164 degrees on the exhaust side.
He emphasizes that these numbers are extremely mild, especially to anyone familiar with gasoline performance engines. However, the target here is to move the engine's horsepower peak from 3,300 rpm to 3,800 rpm, which is fully 1,000 rpm higher than the stock horsepower peak. To do that while retaining the stock valve springs, lift had to be limited to 0.400 inch on the Comp cam. Banks says 0.400 inch just barely fits within the stock spring's safe range; any significant increase beyond that would risk coil bind.
The major change is duration. The new cam increases intake duration at 0.050 inch lift to 186 degrees, which is 31 degrees more than stock. Exhaust duration rises to 200 degrees, which is 36 degrees more than stock. Banks characterizes this as a substantial increase in camshaft compared with the factory profile, even though lift only rises modestly.
Banks then explains why the timing changes matter. On the exhaust side, blowdown begins earlier, which is beneficial at higher rpm because there is less time available for cylinder pressure to escape before the piston starts its upward exhaust stroke. Earlier exhaust opening helps the engine clear the cylinder more effectively under those conditions.
On the intake side, the valve also opens earlier, which helps improve cylinder filling. At the same time, the intake closing point is managed carefully so it still closes at the proper time as the piston rises on the compression stroke. Banks stresses that this is critical in a diesel. If the intake valve closes too late, the engine will not build enough compressive heat to ignite the injected fuel properly as the piston approaches top dead center. In other words, the intake lobe cannot simply be made larger everywhere; it has to be shaped to improve airflow without compromising diesel combustion requirements.
Banks closes by putting the new Duramax camshaft in the context of his long-standing interest in cam design. He recalls one of the first engines in which he changed a camshaft: a 40-horsepower Model A Ford. In that build, he increased compression ratio, added an overhead-valve conversion for greater airflow and a higher percentage of cylinder fill, and installed dual carburetors to raise inlet pressure at wide-open throttle. The engine ultimately increased from 40 horsepower to 105 horsepower.
He says the most dramatic part of that transformation was the Windfields camshaft, which raised the engine's usable speed range from roughly 2,200 rpm to around 4,000 to 4,500 rpm. That experience left him fascinated by camshafts ever since. He also contrasts this diesel cam with the high-overlap gasoline hot rod cams of the 1950s and 1960s that produced a rough, lumpy idle. This Duramax cam is not intended to create that kind of behavior. Instead, its value is in significantly increasing valve open time, with a modest lift increase and much more duration on both the intake and exhaust sides. Banks ends by saying he is eager to install it in the L5P and see how it changes the engine's performance.