Chances are you've heard of the Racing Head Service. Back in 1967, RHS started out life as a manufacturer of racing cylinder heads but soon grew into a full-service operation, offering turnkey engines and performance parts for race cars. According to company literature, it was among the veryfirst to offer crate engines and mail-order performance parts. During the '70s and '80s, RHS made quite a name for itself in circle-track and drag racing. In 1976, RHS started a little company called Competition Cams. Given the relationship between cylinder heads and cam profiles, the RHS/Comp Cams combination made for one heck of a one-two punch. RHS and Comp Cams enjoyed years of performance productivity in NHRA and short-track competition with their performance heads and valvetrain components. Sometime in the late '90s, ownership change and company realignment allowed RHS to slip into inactivity, all but retiring an automotive icon. Resurrected as part of the Comp Cams group, RHS acquired the resources of Pro Topline, including a high-tech cylinder-head foundry in Auckland, New Zealand. This was the start of a return by RHS to its position in the market as an innovator and producer of high-performance heads.
RHS offers a wide variety of cylinder heads for small- and big-block Chevy applications; our test involved heads from the new Pro Elite series. Like many aftermarket sources, RHS offers its LS1/ LS2 heads in two port volumes, since one cylinder head is definitely not ideal for all applications.In addition to the 210- and 225cc intake-port volumes, it is also possible to alter the combustion chamber size from 62cc all the way down to just 36cc. The massive change in chamber volume is possible thanks to a generous deck thickness of 0.800 inch (roughly twice the factory LS1 head). This not only allows dramatic changes in the combustion chamber size (and attending static compression ratio), but also makes the RHS heads ideal for forced induction or nitrous applications, where elevated cylinder pressures can distort the thinner factory heads. The use of the two intake-port volumes allows the RHS Gen III heads to be run on a wide variety of power levels and displacements, as a head designed to feed a stock 5.7L LS1 would not be the ideal choice for a high-rpm 427 stroker.
While the RHS Gen III heads obviously feature full CNC porting to improve the flow rates considerably over a production head, the RHS heads are much more than a set of ported stockers. Starting with a fresh slate, the dedicated RHS castings offer a number of desirable features in addition to big flow numbers. The Power by Design Gen III heads feature altered valve angles. Rolling the valve angle back from the 15 degrees used on the production heads down to 11 degrees greatly improves airflow. The altered valve angle also increases piston-to-valve clearance, allowing RHS head owners to run wilder cam profiles without resorting to notching (or replacing) their existing pistons. Remember that a typical small-block Chevy runs a 23-degree valve angle and the hot small-block race heads dropped this down to 18 degrees. In addition to the change in valve angle, the RHS heads also feature improved valve-guide material and hardened valve seats to extend durability. Another trick feature is the raised (0.500) valve-cover rail. The extra material provided the necessary clearance for aftermarket rockers without resorting to aftermarket valve covers or valve-cover spacers-or hacking the insides of your stock valve covers.