At this point, the stock L5P camshaft is the restriction. If we want this engine to pull harder at higher rpm on stock internals, the valves have to stay open longer so the cylinders can keep filling. That sounds simple until you look at the hard limits: valve-to-piston clearance, spring travel, lash, and valvetrain deflection. We measured the real clearance in the engine instead of guessing from paper specs. The tightest checks came in around .050-inch on the intake and .065-inch on the exhaust at top dead center, and the stock cam already uses part of that window near TDC. That means any new cam has to be designed around actual piston and valve motion, not just advertised lift numbers. The stock valve springs set another limit. With the available travel to coil bind, the target lift has to leave enough margin for lash and deflection. So the job here is not a wild cam. It is a cam that moves the horsepower peak higher, works with the stock lifters, pushrods, rockers, springs, keepers, and retainers, and does it without turning the valvetrain into the failure point. Fuel system capacity was also increased with an S&S high-pressure pump and larger injectors, but air still leads the plan. If the engine is smoke-limited, the camshaft has to help the heads move more air before the extra fuel can do its job.
The video opens with a reversal of an earlier promise not to go inside the engine. After testing, it had become clear that the L5P Duramax was badly limited by the stock camshaft. The goal was not to build a radical valvetrain package, but to find out what a camshaft change could accomplish while keeping the rest of the hardware stock: lifters, pushrods, rockers, valve springs, keepers, and retainers. That constraint shaped the entire engineering exercise. The intent was to move the engine's usable airflow and power higher in the rpm range without introducing incompatibilities or requiring a full valvetrain redesign.
Before discussing cam timing and valve clearance, the recap turns to the L5P head gasket because many people had assumed the engine program would have damaged the head gaskets. The claim here is that the 2017-up L5P uses a substantially better head gasket than earlier Duramax engines. Two major changes are highlighted. First, the compressed head gasket thickness increased by about 0.010 inch. Second, piston projection above the deck also increased by about 0.010 inch. Earlier engines typically had about 0.012 inch of piston projection, while the L5P projects about 0.022 inch.
GM still uses three gasket thicknesses to account for piston projection variation. On the L5P, the nominal compressed thicknesses are 0.047 inch for the A gasket, 0.049 inch for the B gasket, and 0.051 inch for the C gasket. On 2016-and-earlier engines, the corresponding values were 0.037, 0.039, and 0.041 inch. Despite the thicker gasket and greater piston projection, the nominal piston-to-fire-deck clearance remains about 0.027 inch, or 0.7 mm, across the Duramax family.
The extra thickness was not used to increase clearance; it was used to build a stronger gasket structure. The explanation given is that a thicker multi-layer gasket can provide better spring-back behavior through thermal cycles and under firing pressure. Every combustion event stretches the head bolts slightly, and the gasket must maintain sealing as the joint moves. The L5P also adds two head bolts at the corners, increasing clamping load. Taken together, these changes are described as making the L5P roughly 20 percent more capable in terms of cylinder pressure handling. The stated maximum cylinder pressure rises from about 150 bar on earlier engines to about 183 bar on the L5P. In this particular program, cylinder pressure had already reached roughly 260 bar or slightly more without a head gasket failure.
To understand how much camshaft could safely be added, the team prepared a cutaway cylinder head and used it to directly measure valve-to-piston clearance. The cutaway makes the intake and exhaust valves visible, and a dial indicator was placed on an intake valve. The piston was brought to top dead center, and checking springs were installed in place of normal valve springs so the valves could be pushed open by hand. This allowed direct measurement of valve drop and valve-to-piston clearance around top dead center.
The tightest measured clearances found in the engine were about 0.050 inch on the intake and 0.065 inch on the exhaust. Those numbers varied somewhat from cylinder to cylinder, but they established the practical limits for cam design. The point of the exercise was simple: if the camshaft is changed to hold the valves open longer or lift them higher, the valves must not contact the piston. The cutaway setup turned that from a theoretical concern into a measurable boundary.
Because camshaft design depends on crank angle accuracy, the team first established true top dead center mechanically. Changing the camshaft in an L5P requires removing the heads and front cover, so with the heads off they installed a degree wheel and a positive stop. The stop was mounted on a bridge with no head gasket in place. The piston was rotated into the stop from one direction, then from the other direction, and the angle between those two stop points was measured. Halfway between them is true top dead center.
Once top dead center was established, the degree wheel and pointer could be used to map valve motion relative to piston position. A head was then installed, and measurements were taken on number one cylinder. Valve drop and valve-to-piston clearance were checked from roughly 10 degrees before top dead center to 10 degrees after top dead center, effectively degree by degree through the critical overlap region. This process defined how much clearance existed as the piston approached and passed top dead center, which is where intake opening and exhaust closing events become most critical.
The measured 0.050 inch intake clearance and 0.065 inch exhaust clearance at top dead center are not simply empty space above the piston. They are the sum of two geometric factors: the distance from the piston crown, at its projected height, to the cylinder head fire deck, and the amount the valve face is recessed into the cylinder head. Because the valves are sunk below the fire deck rather than flush with it, both dimensions contribute to total valve-to-piston clearance.
The stock camshaft already consumes part of that available clearance near top dead center. The tightest region occurs roughly 5 to 6 degrees before and after top dead center. The measured clearance trace shown in the video spans from about 30 degrees before top dead center to 30 degrees after top dead center, but the danger zone is concentrated around overlap. The stock cam traces were measured with valve lash set at 0.012 inch on both intake and exhaust, so the plotted lift is net valve lift after lash. What the trace does not include is valvetrain deflection. Under real operating load, pushrods, rockers, and related components flex, so about 0.015 inch is commonly added as a safety allowance when evaluating minimum clearance.
The purpose of the new camshaft was to move the horsepower peak from about 2,800 rpm to 3,800 rpm. Achieving that requires more airflow at higher engine speed, which generally means keeping the valves open longer. The team planned to compare conditions at 3,400 rpm, the speed where the engine had already produced 912 horsepower, to see what additional cam timing could contribute.
The conclusion from prior testing was that the engine was not only out of camshaft, but also out of high-pressure fuel pump. The stock Denso injection pump had become a limiting factor, so it was replaced with an S&S Bosch 14 mm stroker pump. The injectors were also changed from S&S 50 percent over units to 200 percent over injectors. Even with those fuel system upgrades, the engine remained smoke-limited, meaning airflow had to increase before the extra fuel could be used effectively. That is why the camshaft became the next priority. The working assumption was that the engine might need roughly 20 percent more open time on both intake and exhaust, although that was still subject to what the mechanical limits would allow.
Camshaft ambition was constrained not only by piston clearance but also by the stock valve springs, since the plan was to retain them. Mike tested multiple sets of stock L5P springs, including springs with different color coatings identified as pink and green. Both types came from L5P builds. At an installed height of 1.614 inches, average seat pressure was about 95.5 pounds. At 0.400 inch lift, open pressure was about 178 pounds. That puts the spring rate at roughly 210 pounds per inch.
The measured coil-bind limit also mattered. The highest coil-bind dimension observed was 1.186 inches. Subtracting that from the 1.614-inch installed height gives 0.428 inch of total available travel before the spring stacks solid. In theory, lifting the valve 0.428 inch would put the spring into coil bind, which is unacceptable. The intended camshaft target was about 0.400 inch gross lift, leaving 0.028 inch to coil bind.
Valve lash changes the real margin. The intake lash would be 0.012 inch and the exhaust lash 0.016 inch, so the tighter case is the intake side. Adding the 0.012-inch intake lash to the 0.028-inch remaining travel yields 0.040 inch to coil bind with no valvetrain deflection. If the usual 0.015 inch of deflection is added, the effective hot running margin becomes about 0.055 inch from coil bind. That established a practical ceiling for lift while staying with the stock springs.
The cutaway head was built to show the difference between theoretical calculations and what actually happens in the engine. On paper, cam timing, lash, lift, piston position, and spring travel can all be modeled. But the visualized setup lets the team see valve action relative to the piston with the real valve gear in place. That matters because the final camshaft must satisfy every limit at once: piston clearance, lash, spring travel, and deflection.
The recap ends at that point in the process. The engineering groundwork had been laid by documenting the L5P's stronger head gasket system, measuring true valve-to-piston clearance around top dead center, identifying the rpm and airflow goals, and defining the stock spring limits. The next step would be to use those real measurements to shape a camshaft that increases airflow and shifts the power peak upward without crashing the valves into the pistons or driving the stock springs into coil bind.