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RHS Hottest New Cylinder Heads and Blocks

How it Works

Stephen Kim Nov 18, 2013
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These days, RHS keeps setting the Gen III/IV market ablaze with the recent launch of its LS Race Block and all-new Pro Elite LS7 cylinder heads. As the older generation of hot rodders will tell you, however, Racing Head Service has a storied history that goes way back. Founded in 1967, RHS quickly became one of the leaders in cylinder head port development with a tremendous amount of success in drag racing and circle track. As the company evolved into a complete engine supplier, it realized that there was a void in the industry for performance camshafts. Consequently, RHS created the COMP Cams division in 1976, and it was eventually split off into a separate entity. RHS went dormant in the '90s, but COMP Cams retained the rights to the RHS brand. When the time was right in the early '00s, RHS was revived as a member of the COMP Performance Group.

The resurrection of RHS coincides with the COMP Performance Group's acquisition of Pro Action cylinder heads. Recognized by both casual cruisers and hard-core drag racers alike as offering exceptional performance for the dollar, Pro Action developed a cult following in the marketplace. After becoming part of the COMP Performance Group, Pro Action was able to leverage its new engineering and manufacturing resources to expand its cylinder head line and take the company to the next level. Today, the RHS/Pro Action tandem is on top of their game, and the horsepower-hungry public are the beneficiaries. To learn all about the company's newest products and the cutting-edge technology that goes into developing them, we recently had an in-depth conversation with Kevin Feeney of RHS.

LS Race Block Development
RHS has been long known for its high-performance cylinder heads, but it shocked the hot rodding community with the launch of the LS Race Block. Recognizing an opportunity to give racers what they want, RHS decided to enter the aftermarket LS block market. "The LS platform has been growing by leaps and bounds over the last several years, and while the OE blocks are a very good piece for most naturally aspirated street applications, they are limited in maximum cubic inches due to their low deck height. Additionally, the trend toward boosted applications is growing, and engine builders are easily able to reach power levels that exceed the strength of the OE block," Feeney says. "The aftermarket had been reluctant to make an LS block due to the complexity of the design, but at RHS our engineers were confident that with the right foundry partner we could make significant improvements to the design. Our goals were pretty straightforward: Design a block robust enough to withstand the abuse of boosted applications, the ability to accommodate more cubic inches, and maintaining compatibility with Gen III and Gen IV small-block components and accessories while still fitting under the cowl of a stock Corvette and Camaro."

Rhs Engine Block 2/10
We strive to achieve a port design that provides an engine with a properly balanced port. The result is great horsepower that doesn't sacrifice torque and driveability.

Built for Power
The RHS LS Race Block has become very popular in max effort race motors. This is no coincidence, as several design elements incorporated into the casting maximize durability without a dramatic increase in weight. RHS engineers point out that the key to the block's strength is in its unique casting design. "We partnered with Grainger & Worrall—a top-notch foundry that uses the Cosworth foundry technique—due to their wealth of experience in high-horsepower, thin-section casting designs. The block has a lot of triangulation in the exterior design to strengthen the case," Feeney explains. "We also spent a tremendous amount of time on the design of the water jacket, and in maintaining equal wall thickness on the parent bore. This provides the most support possible around the pressed-in liner to maintain ring seal. We also chill the bulkheads and inner bore sections to provide the highest metallurgical properties possible. Though the exact power levels the RHS block can handle are not known, in boosted applications we have numerous customers putting 2,000-2,500 hp through them."

Max Displacement
People who buy aftermarket blocks are typically seeking maximum displacement. With this in mind, RHS engineers have incorporated several features that make the LS Race Block very accommodating of large cubic-inch applications. "The first thing we did is increase the deck height to 9.750 inches, which is 0.500-inch taller than the OE design. This was the tallest we could go and still fit under the factory cowl of late-model applications," Feeney says. To make the block more accommodating of long-stroke crankshafts, RHS engineers raised the camshaft up in the block and designed a priority main oiling system that relocates the main oil galley outboard. This allows for a stroke as long as 4.600 inches to easily swing inside the crankcase with a standard 2.100-inch rod pin. "We also maximized the cylinder liner length to provide the best possible piston skirt support. Between the added deck height and longer stroke, the block is capable of 502 ci. We also added many features, such as the capability of running piston oilers, Gen I small-block motor mount boltholes, and a motor plate bolt feature for all-out race applications."

Rhs Engine Block Three Quarter 3/10

CT Scan
RHS goes to great lengths to ensure stringent quality control in each LS Race Block that it ships. In fact, each block undergoes a CT scan during the manufacturing process. "The benefit of performing a CT scan is that it lets us know exactly what the wall thicknesses are after the part is made," Feeney says. "This information allows us to target the machining of the casting to maximize the wall thickness of the machined part in all of the critical areas, particularly in the cylinder bores. Not only does this maintain even wall thickness, it also promotes maximum ring seal."

Rhs Engine Block Aerial 4/10

New LS7 Castings
GM's LS7 castings are arguably the best factory small-block cylinder heads ever conceived. RHS set out to improve upon them with its new Pro Elite LS7 heads, which are available in both 291cc and 307cc configurations. "Improving upon the factory LS7 head design was not an easy task, but we looked outside of the box to determine what could be done to improve it. What we came up with is a raised intake port opening to provide a better line of sight from the intake manifold to the back of the valve," Feeney explains. "The key to making this work was adding material to the intake face to maintain compatibility with the stock LS7 intake manifold. The 291cc head features our standard CNC port, and the 307cc casting is designed to provide additional volume and airflow for larger displacement applications. The ability to build 502ci LS engines these days increases the airflow demand on the cylinder heads, and the 307cc castings are more than up for the challenge. We also incorporated a six head bolt design and increased the deck thickness to provide additional clamping capacity and improve head gasket retention."

Rhs Cylinder 5/10

Raised Runners
Raising the intake runners is a common technique employed to improve intake port airflow. On the other hand, raising the runners too much can compromise the cylinder head casting's ability to support the valvetrain hardware. As such, RHS has employed several strategies in its LS7 heads that offer the superior airflow of a raised runner design while ensuring valvetrain stability. "Raising the intake runners is nothing new, as it has been going on for years and the improvements seem to apply to just about every application. It is effective because it improves the line of sight, and gives the air/fuel mixture a straighter shot from the intake manifold into the cylinder," Feeney says. "The key is to be able to package the raised runner into the existing envelope so you can still utilize the stock valvetrain. Otherwise a custom rocker system is required, which raises costs significantly. In the case of the LS7 heads, the OE rocker design is very good. Consequently, we designed our head to use a rocker stand versus the cast-in pedestal the OE head uses. This strategy allows engine builders to use the stock rockers with a bolt-on stand while retaining the option of installing an aftermarket shaft-mount system for greater adjustability and longer valves in high-lift applications."

Cylinder Sealing
Both the RHS block and LS7 heads are configured for six head bolts per cylinder, whereas the factory LS design only has four. Not surprisingly, the six-bolt design has become very popular in power adder applications. "Although we don't have any statistical data to provide on the clamping force, suffice it to say that the four-bolt design is adequate for stock motors and your typical naturally aspirated street/strip combination that makes moderate horsepower," Feeney explains. "However, when you get into the high-horsepower, large cubic inch, and boosted applications, the six-bolt design is essential in increasing the clamping force and improving head gasket retention. In addition, RHS has increased the deck thickness on the block and heads to add additional rigidity in this area."

Rhs Assembled Cylinder Heads 6/10

Gen I Manifold
Despite all the buzz surrounding the LS-series engine platform, RHS hasn't forgotten about the Gen I small-block. The company has recently released an all-new single-plane intake manifold that promises serious performance gains for engine combinations as large as 434 ci. "Our single four-barrel manifold is designed specifically to fit RHS cylinder heads, but it can be used with all small-block Chevy heads. We incorporated multiple bolt patterns so it can be used with early heads as well as late-model heads with the Vortec bolt pattern," Feeney says. "Although a single-plane manifold is typically used on high-rpm applications, we developed a port design that provides power and a strong torque curve throughout the mid-rpm band. This manifold also features an integral water crossover and idle air control circuit, bosses at all four corners for external water lines, and dual distributor bolt bosses. RHS also offers an EFI version of this manifold that utilizes the same external features as the carb, but has cast-in EFI bungs already in place. The bungs have been rolled over to optimize the entry of the injector angle by aiming it directly at the valve stem."

Rhs Valve 7/10

Big-Block Heads
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."

Rhs Cylinder 8/10

Head Selection
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."

Clean Castings
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."

Rhs Cylinder 9/10
Rhs Intake 10/10


Memphis, TN 38118



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