RHS has a variety of big-block Chevy cylinder heads that offer exceptional performance for the dollar. "The Pro Action big-block Chevy cylinder heads have become very popular in recent years. The valve angle on these heads have been rolled 2 degrees over to provide a port entry more conducive to airflow, but they still utilize the stock valvetrain hardware," Feeney says. "We currently offer our big-block cylinder head in a 320cc or 360cc as-cast configuration as well as a 340cc or 380cc CNC-ported configuration. In most street/strip applications, the as-cast heads work great right out of the box. There are many factors to determine the best runner volume for the application, but as a general rule of thumb anything 540 ci and larger will work best with the 360cc head."
Bridging the Gap
Everyone wants a set of spread-port big-block heads, but these race-bred, Pro Stock-inspired castings are cost prohibitive for most hot rodders. On the flip side, conventional 24-degree BBC castings have improved dramatically in recent years. By addressing the inherent shortcomings of the conventional BBC port architecture, RHS has managed to bridge the gap between spread-port and conventional BBC castings. "Traditionally, the choke point of the big-block Chevy cylinder head design has been the exhaust port, so we raised the port up 0.500 inch on our heads to increase the airflow without running a larger exhaust valve. The CNC versions of our heads offers a little more runner volume than the as-cast versions, and as such, airflow is significantly increased because the CNC-machined contours in the port can't be replicated during the casting process," Feeney explains. Yet another infamous quirk of BBC cylinder heads is that they have a "good port" and a "bad port," where one port often flows substantially more air than its adjacent port. "The ‘good port' versus ‘bad port' arrangement is an inherent design limitation based on the traditional siamesed port and valve layout of the big-block Chevy architecture. We have worked really hard to equalize the flow out on both runners, and it comes down to optimizing the quality of flow opposed to just the quantity. Port designers have worked for years to equalize the ports whether it's in the head itself or with the manifold. Another tool we now have to achieve this are four-pattern camshafts."
As with RHS's big-block Chevy cylinder heads, the company's Gen I small-block heads are extremely popular amongst hot rodders seeking maximum performance for minimal investment. The good news is that RHS offers 180, 200, 220, and 235cc castings under its Pro Action label to satisfy the needs of cruisers and racers alike. The downside is that having such a vast selection of heads can make picking the right one a bit more confusing. "We generally recommend our 180cc heads for 262-350ci engines, our 200cc heads for 327-350ci engines, and our 220cc and 235cc heads for 383-421ci engines," Feeney says. "However, choosing the right cylinder head depends on not just the cubic inches of an engine, but also the weight of the vehicle, transmission type, gearing, and carburetor size. Smaller displacement engines can take advantage of larger runner volumes, but they require turning lots of rpm, which is more typical of a race motor than a street motor."
Although RHS/Pro Action offers a number of CNC-ported cylinder heads, its as-cast heads offer exceptional performance right out of the box. What makes this possible is the company's clean cast technology that replicates the target port shape very precisely. "To achieve accurate ports, we use permanent mold tooling that does not have the wear characteristics of traditional sand-cast tooling," Feeney explains. "It also provides us with a smoother finish with virtually no parting lines present in the ports. The result is a head that flows great without having to clean up the casting. In addition, the targeting of the machining is a lot more accurate, eliminating mismatch in the throat area on an as-cast head."