The factory exhaust manifolds were replaced by a set of 1 3/4-inch, long-tube headers.
After running the motor in stock trim, off came the stock LS3 heads to make room for the CNC-ported L92 heads. GMPP sells the CNC-ported L92 heads with stock valvesprings. While adequate with the stock cam, they are insufficient for performance use with almost any aftermarket cam, including the more than 0.600 lift from the stick supplied by Comp Cams for this test. The Comp Xtreme Energy hydraulic roller cam featured a 0.617/0.624 lift and a 231/239 duration at 0.050. The wide, 113-degree lobe-separation angle improved idle quality and will work equally well with the displacement hike and forced induction we have planned for this combination. In terms of valvesprings, GMPP offered a set of LS6 springs as an upgrade for the stock springs supplied with the CNC-ported heads. Unfortunately, they actually provide little (if any) additional spring pressure over the stock springs. What they do offer is additional lift before coil bind, but even these were deemed insufficient for use with our high-lift Comp cam. Rather than risk valve float, we replaced the stock springs with a set of beehive springs from Comp Cams. The Comp spring upgrade offered an increase in seat pressure of 30 pounds over the factory springs. Not wanting to reuse the torque-to-yield factory head bolts, the CNC heads were installed using Fel-Pro head gaskets and ARP head studs.
Given the mild cam timing and already impressive flow figures offered by the stock LS3 heads, we suspected the head upgrade would offer only minor power when combined with the stock cam, and we were right. Running the CNC-ported heads on the otherwise stock LS3 resulted in a jump in peak power from 492 to 503 hp. Peak torque was up slightly, from 484 lb-ft to 497 lb-ft, though at a slightly higher 4,900 rpm. What was not expected with this combination was the fact that the CNC-ported heads from GMPP improved the power output throughout the tested rev range, from 3,000 rpm to 6,500 rpm. The LS3 now offered a peak of nearly 500 lb-ft, and the torque curve bettered 450 lb-ft from 3,600 rpm to 5,900 rpm, making for an exceptionally broad torque curve. Given the already impressive flow figures and port volume of the stock LS3 heads, a cam would be a better choice than ported heads if you had to choose one or the other. But as we shall see, the combination offered some serious power.
On the cam side, the factory LS3 cam was secured to the timing gear via a single retaining bolt. Most aftermarket LS cams (including ours from Comp Cams) still feature the early three-bolt retaining pattern, so it was necessary to replace the factory upper timing gear with a new version that featured the three-bolt pattern and the requisite cam sensor lobes. The cam sensor is located on the back of the cam on early LS motors, but the LS3 featured a cam sensor mounted in the front cover. The new timing gear was available directly from GM for less than $30. The factory hydraulic roller lifters, rockers, and pushrods were reused with the new GMPP heads and Comp cam. Cam swaps on LS motors are simple, especially on the engine dyno, as they do not require removal of the intake manifold or lifters. Simply rotate the cam and the plastic retainers will hold the lifters in place while you swap the cams. The Comp cam upgrade not only improved the peak power numbers significantly but also offered gains throughout the rev range, from 3,000 rpm to 7,000 rpm. Big chunks of power came after 4,000 rpm, but even down at 3,000 rpm, the cam offered an additional 4-6 lb-ft. Impressed as we were with the head and cam upgrade on the GMPP LS3, we couldn't help but wonder what it would be like with a little more displacement and even some boost. Stick around as we add forged internals and a supercharger to the equation.
A cam swap was what the LS3 really needed. The Comp Xtreme Energy hydraulic roller cam featured a 0.617/0.624 lift split, a 231/239 duration at 0.050, and a 113-degree lobe-separation angle. The ported heads responded very well to the high lift supplied by the new cam profile. The cam swap improved the power output of the LS3 from 503 hp and 497 lb-ft to 569 hp and 522 lb-ft. Despite the healthy cam specs, the hydraulic roller cam never lost ground to the factory cam, even down at 3,000 rpm.
Running the air/fuel and timing show was a FAST XFI management system.
Run sans accessories and with the long-tube headers, the otherwise stock LS3 produced peak
After establishing a baseline, off came the factory intake to start our head and cam swap.