You might be wondering why we would choose to modify any components in this strength test, but the answer is a simple one. The power output of any turbocharged motor is a function of the power output of the normally aspirated motor multiplied by the boost pressure (pressure ratio). Your normally aspirated motor is actually running at an atmospheric pressure of 14.7 psi. If you double this atmospheric pressure (by supplying boost from a turbo or blower), you can theoretically double the power output of your motor. This formula works regardless of the original power output. If we were to run the 5.3L in stock trim, the resulting power output would be around 360 hp (on this dyno, the way we test). If we apply 14.7 psi from our turbos to the stock 360hp motor, we might get 720 hp. If, on the other hand, we increase the power output of the motor with ported heads, a cam and intake to 500 hp, then adding 14.7 psi will result in an even 1,000 hp. Having a more powerful normally aspirated motor allows you to produce more power with the turbos at a lower boost pressure. More than just the boost limit of the motor, we wanted a big power number to go along with it.

Wanting big boost and big power to test the limits of the internal components of the stock short-block, we swapped out the stock cam, heads and intake manifold. The mild 5.3L truck cam was replaced by a healthy 281LR HR13 cam from Comp Cams. The LSR cathedral-port grind offered a .617/.624 lift split, a 231/239-degree duration split and a boost-friendly 113-degree LSA. The powerful cam was teamed with a set of GenX 215 heads from Trick Flow Specialties. The GenX 215 heads featured full CNC porting, 215cc intake ports and a 2.04/1.575 stainless steel valve package. The GenX 215 heads were designed for the slightly larger 3.902 bore but worked without interference on the smaller 3.78-inch bore. The GenX 215 heads offered not only exceptional airflow (over 320 cfm), but also a thicker deck surface than the stock 5.3L heads. The heads were combined with a truck-oriented Fast LSXRT intake and matching 102mm throttle body. The dedicated fuel rails were stuffed with injectors that flowed a whopping 160 pounds per hour—we were not lacking for fuel! Wanting to maximize sealing under high boost, we installed a set of Fel Pro MLS head gaskets (.053 thick and 3.950 bore) and ARP head studs. The 64cc chambers on the GenX heads lowered the static compression of our 5.3L by nearly half a point.

After a break-in procedure, Westech’s Ernie Mena dialed in the tune on the 5.3L using the Fast XFI/XIM management system. The normally aspirated 5.3L eventually produced 503 hp at 6,600 rpm and 441 lb-ft of torque at 5,700 rpm. The new heads, cam, and intake shifted the power curve higher in the rev range, as a stock 5.3L will produce peak power at just 5,400 rpm. We were impressed by the power of the little 5.3L, but were anxious to get this thing under boost. We installed a homemade turbo system consisting of a set of JBA shorty truck headers and adapter tubes to mount the T4-based, 76mm turbos from CX Racing. CX Racing also supplied the air-to-water intercooler, aluminum tubing and silicone couplers. They even had all the small parts like oil feed and drain kits, making them and excellent source for the do-it-yourselfer. To properly control the boost on this monster, we relied on a pair of 45mm Hyper Gate wastegates, a manual wastegate controller, and a Race Port blow-off valve all from Turbo Smart.