We ran the LS1 on the Super Flow engine dyno at Westech Performance. Rather than rely on the factory electronics, the modified LS1 was run using a FAST XFI engine-management system, allowing us to dial in the air/fuel and timing curves while simultaneously removing the (restrictive) factory mass-air meter and attending air-inlet system. The idea was to run the motor first with the stock heads and then with the RHS heads.It's important to note that you have two options when it comes to rocker arms. You can reuse the factory rockers, but in order to do so you'll need to order Comp Cams' stud rocker stand, PN 54201-2. The alternative is to go with its line of shaft-mount rockers, PN 1509, perfectly suited for more aggressive applications. Lastly, our mule was optimized with the XFI management system and produced 480 hp and 453 lb-ft with the stock LS1 heads. As we have come to expect of these powerful Gen III motors, the torque production was impressive, exceeding 400 lb-ft from 3,000 rpm (actually lower rpm had we tested below that engine speed) to 6,300 rpm. Try building a conventional 23-degree small-block that makes 480 hp with a 212/218-duration cam.
After running the test motor with the stock heads, off they came, replaced by the new RHS Pro Elite Gen III heads. We like to use ARP head studs when running head tests, but a snafu (by the author) in ordering the ARP hardware forced us to run a set of new stock bolts. Never try to reuse the torque-to-yield bolts, as they will not provide sufficient clamping force on the head gaskets. The RHS heads were installed with a fresh set of Fel Pro head gaskets. After adjusting the Comp rockers and installing the FAST LSX intake, we were ready for action. All we can say is Wow, as the new RHS heads improved the power output of the modified LS1 by as much as 50 hp over the stock castings. All the impressive features included with the RHS heads combined to improve not only the peak power numbers but also the all-important average power production. The new heads picked up power from 3,000 rpm all the way to 6,500 rpm. Torque production from our LS1 test mule now exceeded 450 lb-ft from 4,100 rpm to 6,100 rpm and never dipped below 420 lb-ft. If these Gen III heads are any indication, it looks like the boys from RHS are back in full effect.