With assurance that our test engine was healthy and our baseline numbers out of the way, we tore into the 5.3L for our first round of upgrades. Since we had a number of serious upgrades planned for the engine and limited dyno time, we had to take the shotgun approach and install all the performance upgrades at one time. This meant replacing the factory heads, cam, and intake manifold all in one fell swoop. Were we to choose one upgrade from the list to apply to an otherwise stock engine, it would have been the camshaft. Given the already decent head flow, LS motors (especially the 5.3L) will respond more to a cam upgrade than a set of heads or intake manifold (assuming an otherwise stock engine). The addition of a cam does require a laptop tune to keep your truck happy, but the performance gains are definitely worth the upgrade. Since our test engine was destined for truck use, we purposely tailored the modifications to enhance torque production. Huge gains will come later with the stroker short-block and supercharger, but we wanted to keep the normally aspirated package streetable, which meant limiting cam duration. The mild, stock LM7 cam was replaced by a Trickflow TrackMax cam that offered .575 lift, a 220/224-degree duration split (at .050) and a 114-degree lobe separation angle. Trick Flow Specialties also offers a slightly milder grind with a 216/220-degree duration split, but we knew we would be stepping up in displacement with this application, so we opted for the 220/224 cam.
Both the original 327ci small-block Chevy and modern 5.3L share similar displacements, yet they arrive at them differently. The 327 combined a 4.00-inch bore with a 3.25-inch stroke, while the 5.3L mixed a much smaller 3.779-inch bore with a larger 3.662-inch stroke. Unlike the LS1/LS2 and LS3, the small-bore 5.3L required a dedicated cylinder head and valve sizing to optimize flow. Trick Flow Specialties once again had just what we needed in the form of their Trick Flow GenX 205 cylinder heads. As the name implied, the GenX 205 heads offered 205 cc intake ports (flowing nearly 300 cfm), a 2.00/1.575 valve combination and small 58cc combustion chambers to ensure no loss of compression (factory 5.3L heads come with smaller chambers than typical LS1/LS2/LS6 heads). In addition to the tremendous flow potential, the GenX 205 heads featured a double valve spring package that would accept our .575-lift cam and allow the engine to rev cleanly to 7,000 rpm if need be. The new GenX 205 heads were run with the stock rockers and secured using ARP head studs and Fel Pro head gaskets.
The final upgrade applied to our 5.3L truck engine was the FAST LSX intake manifold from FAST. Compared to the stock truck intake, the LSX features a revised runner configuration designed to enhance power production. Typically speaking, longer runners, like those in the stock truck intake, enhance power production lower in the rev range. Our original plan was to run the new LSXRT from FAST, but it did not arrive in time for our first dyno session, so we will test it on the 383ci stroker combination for the next issue.