Big And Tall: Chevy

Big And Tall: Chevy’s RS-X / ZZ632 Big-Block Cylinder Heads Are Huge

The bigger is better philosophy is alive and well with Chevrolet Performance‘s latest big-block ZZ632 performance engine that punches out slightly more than 1,000 horsepower on 93-octane pump gas. Standing tall behind that mound of horsepower is what the engine was built around; a hefty pair of CNC’d aluminum RS-X cylinder heads.

These heads are different than anything GM has designed for production and we wanted to know more about them. So we spoke with the man in charge of production for Chevrolet Performance, Alin Dragoiu, DRE-Performance Parts Global Propulsion Performance and Racing Engines. Prior to this assignment, he worked on Chevrolet’s new engine block for NASCAR and the Cadillac ATS-V.R twin-turbo V6 for World Challenge racing.

The RS-X heads are different than anything GM has produced for the aftermarket with their raised, spread ports. They are more similar to LS heads than anything else.

Pro Stock Roots

Dragoiu says the original cylinder head design started life around 1986 as symmetrical port Pro Stock racing heads. “When they became available, the NHRA rules allowed a different design (4.840 bore spacing), and the heads were ultimately never raced.” 

The heads were not scrapped, however. They were even available in the Chevy Performance catalog for years. Around 2017, Dragoiu says the engineering team started redesigning the current big-block and the big spread-port heads ultimately became the foundation for the RS-X heads. “As a racing head, the freedom was there to explore improvements on the big-block head such as symmetrical ports and different valve angles.”

Port Variations

Traditionally, big-block Chevy cylinder heads have port shape variations from cylinder to cylinder to make room for pushrods and head bolts and such. But the spread port design allowes the intake ports to be the same length, volume (449cc), and layout. The exhaust ports are also identical to each other at 161cc. The head also utilizes titanium valves that measure 2.450 inches on the intake and 1.800 inches on the exhaust, with 5/16-inch. stems. The valve springs are a beehive style with a 1.589-inch diameter. 

The RS-X exhaust-port face is rolled four degrees from the standard big block, and the pattern is raised around 1.1 inches, so custom headers are required. The benefit of the spread port design is that each intake port is now the same across the head.

According to Dragoiu, the biggest difference with the RS-X head is the symmetrical intake ports with a raised and repositioned intake flange. “The intake ports are raised significantly enough to allow a separate valley tray and dry intake manifold. The valve angles are changed from the standard BBC to allow large valves for the best airflow.”

RS-X cylinder head

Here, you can see the raised intake-port design, allowing for a dry intake manifold through the use of a separate valley tray to both seal the oil in the valley and distribute coolant to the cylinder heads.

The new head uses a standard big-block exhaust bolt pattern so a standard header flange will fit, according to Dragoiu. “The RS-X exhaust face is rolled four degrees from the standard big block and the pattern is raised around 1.1-inches, so custom headers are required. The benefit of the spread port design is that each intake port is now the same across the head. Siamese ports require a long/short path to the cylinder so that one port will flow differently than its neighboring port.”

The Godfather

While much of the work was already done prior to Dragoiu coming on board for the project, the man who came up with the original design back in the ’80s was a renowned GM engineer. He gets much of the credit since he initially designed the cylinder head and was subsequently brought back in to refine the heads for the ZZ632. 

“Many people have asked if the LS head was an influence on the big-block head, but the story is a little more complicated than that,” says Dragoiu.

Technically, the LS heads were inspired by this big-block head, because the gentlemen who worked on it, Ron Sperry, designed it back in the ’80s. He also had a pretty important hand in the development of the LS engine. — Alin Dragoiu 

In fact, Ron Sperry is the “RS” behind the RS-X. He is also known as the godfather of the LS engine, among many other accolades in a career that spans back to the 1960s. Sperry retired in 2008 but continued to work with GM on a contract basis for special projects until 2020. 

Raise The Roof

Dragoiu explains that he inherited the ZZ632/RS-X project about halfway through, after Sperry fully retired from GM. “The heads were pretty much designed at that point, we were just going into COVID, and Ron retired around that time. I did have some interaction with him regarding the heads. But when I took over, the shape of the intake ports needed a redesign. We tried a few iterations and ultimately ended up with an older design that worked pretty well.”

The roof of the intake port was raised to allow for a straighter shot to the back of the valve. The first design iteration dropped the floor, which didn't work as expected.

Some of the Computational Fluid Dynamics (CFD) analysis that was done on the head called for more cross-section on the intake port, according to Dragoiu. “[That] was done by lowering the floor, which was not directionally correct. The computer liked it because the numbers came out right, but there’s not a lot of benefit to lowering the floor. We prefer to raise the roof of the port most of the time. So we scrapped that one and went back to the old design that had a slightly smaller cross-section, but still had a raised floor.”

Raising the ports is always a benefit, notes Dragiou. “We get that straight shot to the back of the intake valve and the exhaust as well. We wanted to raise those ports as much as we physically could, which is what actually drives the physical size of the head.” He says that’s why the head is so tall.

RS-X exhaust port

The massive exhaust ports are bigger than some V8 engines’ intake ports, at 161cc.

Dragoiu and his team also adjusted the angles and the positioning of the valves to package the largest valves they could without shrouding the valve. “Obviously, if [the valve] gets too close to the bore, the shrouding ends up hurting us. Everything works as one big compromise to deliver the best package.”

More Applications

The RS-X/632 was a challenging project, says Dragoiu, because it took the whole engineering team’s experience and know-how to achieve 1,000 naturally-aspirated horsepower on pump gas. The result is that it opens up the heads for many more applications in the future. “The RS-X head is versatile enough to work in a performance or racing application,” says Dragoiu. “Due to the small, compact combustion chamber, higher compression ratios for racing are easily achieved with a piston change.”

With relatively small combustion chambers (70cc), the RS-X is able to run on pump gas and crank out 1,000 horsepower in the ZZ632. But the heads will fit on other Bowtie Sportsman blocks and can be bumped up to run racing fuel with a simple piston change.

Currently, the heads are optimized for the ZZ632 with its 4.600-inch bore. The heads will fit most standard big blocks, but Dragoiu says the heads can only accommodate down to a 4.500-inch bore size. “We have tested the heads down to a 4.560-inch bore, and they will physically fit on a 4.500-inch bore without interference.”

The team also added additional valley lug bolts for strength and Dragoiu recommends using them with Chevy Bowtie Sportsman blocks that also have that feature. “The heads will fit any standard bolt pattern big-block, but the only difference is we incorporated four valley lugs. Your typical big-blocks only have two per bank. So as a result, we recommend running these heads on our Sportsman block that has those lugs incorporated.”

The Valley

With the heads being so tall due to the raised ports, there was room to package a separate valley tray underneath. “It makes it nice because removing the intake manifold doesn’t require you to break into the cooling system,” says Dragoiu. “It’s a dry manifold that is O-ringed, so no gaskets are necessary and it’s easily taken on and off.”

The tall RS-X heads allow for a unique way to package the ignition coils on a separate valley plate under the intake. GM engineers say that it is considered a "Coil-Near-Plug" setup and that it keeps the coils out of the exhaust heat so they don't get heat soaked.

On top of the valley plate, Dragoiu’s team also placed eight separate ignition coils for a shorter run to the spark plug. “It’s technically coil-near-plug, but there was a large area to package the coils. The other option was to place the coils in the valve covers, but [the ZZ632] didn’t look as clean doing that. We also had concerns about the heat coming from the headers and heat-soaking the coils. They actually stay relatively cool in the valley.”

Quick Takes

The ZZ632 is pretty much built around the heads, Dragoiu acknowledges when asked about how much power potential is in the heads. “When the 632 project first started, we were looking into different heads that we could use from different sources. And that’s when somebody suggested that we have this head design that has kind of been sitting around for quite a few years. Someone asked, ‘what if we just incorporated it into the 632?’ Because we needed a very high-performance head in order to make the power. So it just worked out that way. Once we went in that direction, then everything else like the manifold and so forth was designed around it.”

RS-X heads will come in three different packages, one of which will be fully assembled with shaft-mounted rockers. The coils are neatly packaged on a separate valley plate underneath the high-rise intake manifold.

Currently, the GM single plane manifold (P/N: 19366614) is the only one that fits the RS-X. But Dragoiu says he’s confident that the aftermarket will catch up as it starts getting out there. “A custom manifold is easy to fabricate if a customer would like a different manifold.”

Tall Mountains

The single-plane Chevy Performance manifold is tall sitting on top of the tall cylinder heads, and then adding a Dominator-style throttle body on top of that makes clearance for most cars an issue. But most of the ZZ632s will probably go into race cars or trucks where that won’t be a problem. However, Dragoiu says they did consider the height early on.

RS-X cylinder heads flow almost 500 cfm at .787 inch of lift due to the tall, straight ports. Dragoiu says customers may experiment with the bare, unported head to develop different ports or run different valve sizes. But don’t expect to order them right away. The majority of the heads are slated for the ZZ632 until some inventory is built up.

We tried some lower bathtub-style manifolds, but in the end, it just hurt the power too much. — Alin Dragoiu

GM engineers couldn’t quite get over the 1,000 horsepower mark with a bathtub manifold, says Dragoiu. “Eventually, we just said it’s going to be a tall engine regardless, and trying to save an inch here probably isn’t worth it. We just left it where it wants it to be.”

Dragoiu’s team was constantly moving things and trying different simulations to get to the best setup for the RS-X/632, and the result was cylinder heads that flow almost 500 cfm at .787 inch lift, and an engine that makes more than 1,000 horsepower on pump gas. The sky is the limit for where the RS-X heads land next.

Chevrolet Performance will offer the heads in a CNC-ported assembled head just as they arrive on the ZZ632, a CNC-ported bare head, and an unported bare head with guides and seats in a bag. Dragoiu says customers may experiment with the bare, unported head to develop different ports or run different valve sizes. 

But it might be a minute before anyone gets to play around with the RS-X heads. “We haven’t released them for sale yet,” Dragoiu remarks. “At the moment, I think they’re all slated for 632 builds. But as we build up inventory, then we will open up sales at that point.”

Fully machined and assembled specs:

  • 449cc intake port
  • 161cc exhaust port
  • 70cc combustion chamber
  • Titanium 2.450-inch intake, 1.800-inch exhaust valves with 5/16-inch stem OD
  • Ovate wire-type beehive valve springs with 1.589-inch OD (large end)
  • Steel 10-degree retainers with 1.115-inch OD
  • Standard big-block exhaust bolt pattern.

Article Sources

About the author

Brendan Baker

Brendan Baker is an automotive writer who lives in Akron, Ohio with his wife and two dogs. He started racing and building cars at a young age, building his first "racecar" at age 12 (a quarter-midget), which he put on pole position in its first race.
Read My Articles

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