The CNC porting of the RHS Pro Elite Gen III heads maximizes flow rates. This program includes precision machining of the intake and exhaust ports along with optimizing the combustion chamber design. When combined with 2.04-inch stainless intake and 1.57-inch exhaust valves, the result is impressive numbers. The smaller 210cc RHS heads offered well over 300 cfm on the intake.In fact, according to data supplied by RHS, the 210cc heads flow 323 cfm at 0.650 lift and 320 cfm at a more realistic 0.600 lift. But RHS has been in the business long enough to know there is much more to a good cylinder head than just big flow numbers achieved at max lift values. The RHS 210cc heads exceeded 300 cfm at 0.500 lift while still offering impressive low- and mid-lift flow (see airflow data). The exhaust flow numbers are equally impressive, though the numbers generated would have been much higher had RHS tested the heads with a flow pipe on the exhaust. Flowing 214 cfm without the aid of a flow pipe is pretty remarkable, since all that intake flow must also find its way out. Try coaxing 320 cfm out of your old Fuelie, or even an L98 head, and you'll come to appreciate just how impressive these new Gen III RHS heads really are.
While the RHS Pro Elite Gen III heads sounded like a serious performance piece on paper, the proof, as they say, is in the pudding. In this case, the pudding was a direct back-to-back test on the engine dyno. What better way to illustrate the power gains offered by a set of heads than a direct comparison? To put the new RHS heads through their paces, we first selected a suitable test motor. Our LS1 started out life as a GM Performance Parts 5.7L crate motor. Originally destined for the now-defunct (hopefully soon-to-be resurrected) F-body, the 5.7L came as a complete ready-to-run engine assembly. Not content to test the heads on a stock motor, we made a few modifications to the LS1 first. Replacing the stock parts were a set of Hooker long-tube headers feeding a pair of 3-inch Magnaflow mufflers; a Keith Wilson-designed FAST LSX intake with matching 78mm FAS tthrottle body; and an XR265HR grind from Comp Cams, which offered a 0.522/0.529-lift split, a 212/218-duration split at 0.050, and a 114-degree lobe separation angle. Mild as performance cams go, the XR265HR cam is both streetable and powerful, a perfect combination for our test motor.