Elite Performers

: Nostalgia Pr Street brought us two of the biggest players in the class, with Chuck Demory and Jeff Colletta lining up it was sure to be a drag race. Demory had been on a roll all weekend and this pass was no different as the team blasted off another 7.29 lap as Jeff Colletta shut it down early.

Bolt on RHS Pro Elite LS7 heads for tremendous boost

Words And Photos: Stephen Kim

RHS offers its Pro Elite LS7 cylinder heads in 291cc and 307cc configurations to suit a wide range of street and race applications. They’re available fully CNC-ported or as raw castings. For older 3.900-inch-bore LS motors, RHS offers a 266cc small-bore variant as well. All Pro Elite LS7 heads are compatible with both stock and aftermarket intake manifolds.

Squeezing another 20-30 hp out of a set of mediocre Gen I small-block Chevy cylinder heads is simple; just open up the bowls and back-cut the valves. But, upping the ante to a set of GM LS7 castings and wringing out any additional airflow can prove difficult. RHS has welcomed the challenge and cast their own LS7 heads.

Arguably the best factory small-block heads ever built, the GM LS7 castings move 360 cfm through raised runners. 12-degree valves, factory CNC porting, and 2.200-inch titanium intake valves further add to the mystique. However, while they perform exceptionally well on a 427c.i. motor, today’s crop of mega-displacement race engines can easily push them past their comfort zone.

Since the LS7’s release in 2005, options for aftermarket blocks and stroker crankshafts have exploded, and spawned an equal growth in engine displacement. Today’s LS race engines can easily exceed 500c.i., and when matched with modern valve train hardware that can turn 8,000-plus rpm. Keeping the cylinders filled at elevated engine speeds requires some serious airflow.

RHS started with a clean-sheet design to significantly improve upon GM’s LS7 cylinder heads with its Pro Elite Big Port LS7 cast-ings. Some key enhancements: CNC-ported 307cc intake runners, raised intake port entrances, massive 2.250/1.615-inch valves, beefy .750-inch-thick deck surfaces, and reinforced rocker rails.

In addition, RHS enlarged the intake ports from 275- to 307cc, and raised the port entries .220 inches higher than stock. The straighter flow path to the valve seats significantly enhances performance potential, and the RHS castings boast plenty of cross-section to support large-displacement combinations.

“The stock LS7 heads are very impressive, and since they are already CNC ported from the factory, there isn’t a lot left on the table,” Kevin Feeney of RHS explains. “We had to look outside the box, which is why we decided to raise the intake runners. This provides a much straighter line of sight for the intake charge as it travels into the combustion chamber.”

Bolt-in simplicity, enhanced durability

Raising the height of the intake ports is one of the most effective methods of improving cylinder head performance, but that often creates the need for intake manifolds designed specifically for the repositioned ports. To eliminate this added expense, RHS de-signed the Pro Elite heads to maintain compatibility with standard LS7 intake manifolds.

“From the very beginning, the RHS LS7 heads were built to accommodate a stock or aftermarket intake manifold designed for standard-location ports,” says Feeney. “To accomplish this, we added material to the intake face so the cylinder heads can maintain proper port alignment without having to use spacer plates.”

Raised intake ports provide a straighter flow path from the port entrance to the valve seat, which alleviates load off the short-turn radius and improves airflow. In a combo like this Real Street 451 that will eventually see a lot of nitrous, RHS’ beefy castings and .750-inch deck ensure positive head gasket seal. To accommodate the wide range of applications the big-port 307cc castings (PN: 54504) are intended for, they’re sold bare so racers can customize them to the specific demands of their combination.

On the durability front, perhaps one of the biggest downsides of porting a factory cylinder head is compromised integrity due to removal of metal. This is of particular concern at the roof of the runner, where porters trying to improve line of sight at the port en-trance risk grinding into the valve spring pockets. Likewise, the elevated cylinder pressure and spring pressure of race engines are subjected to place additional stress on the head casting. Consequently, RHS fortifies its Pro Elite LS7 cylinder heads in several key areas to maximize casting durability.

“In addition to raising the intake ports, we also raised the roof of the head to maintain spring seat thickness, and to provide adequate installed height for the tall valve springs required in high-lift applications,” Feeney explains. “We also reinforced the entire rocker rail area for additional valve train stability and to support aftermarket shaft-mount rocker arms. Head gasket retention is critical in high compression and boosted applications, so the RHS LS7 heads feature much thicker decks and a six-bolt head design.”

Air quality, not quantity

Without question, the flow bench has dramatically accelerated cylinder head development in the last decade. However, factors such as port velocity, cross-section, and chamber efficiency are often as important as peak airflow numbers.

“The quality of airflow is more important than the quantity,” said Feeney. “The key to making lots of power is optimizing the combination of runner volume, cross-sectional size and valve diameter to design a balanced port that will maximize power and torque for the intended application without sacrificing throttle response. All these factors went into designing the Pro Elite 307cc castings specifically for larger cubic inch applications. Increasing the intake valve size to 2.250 inches complements the larger bore diameter of big displacement race engines very well. Compared to stock, the overall increase in cfm of the RHS heads might not be dramatic on a flow bench, but they still net a big increase in horsepower.”

: In Mean Street we saw an incredible match-up as Jeremy Gillian and Alan Von Ahnen pulled to the line. It was neck and neck til the finish line were Gillian treed Von Ahnen both running 10.02.

Dyno test

While analyzing specs indicate potential performance gains, nothing settles the score like a real-world dyno test. To find out how much of a horsepower boost the RHS Pro Elite cylinder heads are worth over a set of stock LS7 castings, we tagged along as the School of Automotive Machinists & Technology (SAM Tech) bolted them to a 451c.i. LSX-powered 1995 Camaro.

Built to compete in the NMCA LSX Real Street class, the Camaro serves as the ideal test bed. Not only has the Camaro reached the limits of the factory LS7 heads, it needs a big increase in horsepower to keep pace with the competition in Real Street.

: At the end on the day in Street Radial it would be Wisconsin based Jay Canella and the southern boy Mike Fratena. Both running very consistant this weekend it was sure to be a great round, but it was Mike Fratena all the way down as he blasted to an 8.64 leaving Jay Canella behind.

When the Camaro’s 451 was built by Late Model Engines in 2010, the first aftermarket rectangle-port LS cylinder head castings started trickling into the marketplace. However, the 360 cfm dished out by GM’s factory LS7 heads were deemed more than suffi-cient to run competitively in Real Street. The crew at LME still improved upon them, hand-porting them to 399 cfm on the intake side and 256 cfm on the exhaust side, at .700-inch lift. Matched with a custom 254/260 hydraulic roller camshaft featuring .646/.630-inch lift, the combo cranked out 720 hp on the engine dyno. The Camaro ripped 10.20 seconds at 137 mph on the track.

Those numbers were more than respectable back then, but the NMCA Real Street competition has gotten much faster. To help the dated 451 keep up, SAM Tech was tasked with updating the combination with a set of 307cc RHS Pro Elite LS7 castings and a custom COMP Cams 260/274 solid roller. Considering the factory LS7 cylinder heads on the 451 have been ported to flow an addi-tional 39 cfm over stock, the RHS castings clearly had their work cut out for them.

At the end of the dyno session, the RHS Pro Elite LS7 cylinder heads, combined with the custom COMP camshaft, bested the set of ported GM LS7 heads by 59 rwhp, for 625 hp total. Factoring in a standard 20-percent driveline loss equates to a 74 hp increase at the crank. Not bad for a day’s work.