Inside Look At The Chevrolet Performance ZZ632

Like many of you, late last year I received an email that started with three simple words: Bigger. Bolder. Badder. The correspondence was announcing the new Chevrolet Performance ZZ632/1000 big-block crate engine. With slightly more than 1,000 horsepower, the ZZ632 is Chevrolet Performance’s most powerful crate engine ever. What’s more, it comes with the modern convenience of electronic fuel injection, a crank-trigger ignition, coil-per-plug spark delivery, and can provide all those ponies while gulping on 93-octane pump gas. In a world that is clamoring to “go green”, performance junkies can rejoice that the internal combustion engine is alive and well.

The ZZ632 uses the same block as a foundation that is found in the ZZ572, albeit it does receive some massaging to accommodate the larger stroke and bore.

“This is the biggest, baddest crate engine we’ve ever built,” says Russ O’Blenes, GM director of the Performance and Racing Propulsion Team. “The ZZ632 sits at the top of our unparalleled crate engine lineup as the king of performance. It delivers incredible power, and it does it on pump gas.”

Although 7,000 rpm is the recommended rev limit for the engine, it actually achieves its peak 100,4 horsepower at 6,600 rpm. Peak torque of 876 lb-ft is realized at 5,600 rpm, and the engine produces over 600 lb-ft of it at just 3,000 rpm.

But what makes a ZZ632? What’s inside this mega-inch street engine? We were fortunate enough to get an inside look at one of these mills going together and thought you guys might also like to see what goes inside as well.

Inside is a forged crankshaft with a 4.750-inch stroke.

A Repurposed Foundation

When looking at the outward appearance, one might not realize the ZZ632 shares the same tall deck, splayed four-bolt-main iron block as Chevy’s slightly smaller ZZ572 crate engine. However, it has a bore of 4.600 inches and utilizes a stroke of 4.750 inches. To provide the clearance needed for that longer stroke, engineers needed to slightly modify both the block and the connecting rods.

In case you were wondering, the connecting rod length is 6.660 inches and the piston's compression height is 1.165 inches.

Robust Rotations

The crankshaft (P/N 19366600) is an internally balanced forged 4340 steel piece, so keep that in mind when you order your flywheel or flexplate. Next on the parts list are the connecting rods (P/N 19432392). In a world that seems to favor powdered-metal construction, that was not an option for the ZZ632. For this engine, only a set of steel H-beams would do. While a stock 454 connecting rod is 6.135 inches, the rods in the 632 measure 6.660 inches.

When it comes to pistons, the choices are seemingly endless. But, in this engine, squeezing the air-fuel mix is a set of 2618-alloy forged pistons with a Grafal coating on the skirts (P/N 19366601) to create a streetable 12.0:1 compression ratio. Wait. What? How did they make a 12:1 compression ratio streetable? It all comes down to using at least a 93-octane fuel, precise valve timing, very efficient combustion, and modern amenities (i.e., EFI and the crank trigger).

How many man-hours are needed to assemble one engine? Roughly 20. The rings are filed to fit, bearing clearances checked, and block deburred by hand. All engines undergo a hot start test before shipping.

Keeping the inhale and exhale in check is a hydraulic roller cam (P/N 19432531) with .780/.782-inch lift and 270/285 degrees of duration at .050-inch lift. The cam is ground on a 113-degree LSA which helps bleed off some of the compression, allowing the pump gas to be used. On top of those RSX cylinder heads is a set of shaft-mounted roller rockers with a 1.8:1 ratio.

The camshaft is a hydraulic roller-lifter design With a 113 LSA. This wide LSA helps bleed-off compression while the engine is running to enable the use of pump gas.

According to Alin Dragoiu, DRE-Performance Parts Global Propulsion Performance and Racing Engines, “A small, efficient combustion chamber along with very precise control of ignition timing is utilized to allow the ZZ632 to run on 93-octane pump gas. The fuel and spark timing are fully mapped at full- and part-throttle conditions using combustion pressure transducers. By doing this, we are able to optimize combustion to run right to the edge of knock without going over.”

The symmetrical ports are derived from a previous Pro Stock racing design. Plan on needing custom headers.

A Strange-Looking Pair

One of the first things that everyone first noticed about the ZZ632 was the RSX cylinder heads (P/N 19431810). As evidenced by the odd-looking valve covers, these are not your typical porcupine design. In fact, they are a huge departure from any big-block street head that Chevrolet has ever produced. Originally designed for Pro Stock racing, these high-flowing CNC-machined aluminum cylinder heads feature symmetrical ports for both intake and exhaust. Traditionally, big-block Chevy cylinder heads carry variations in port shape from cylinder to cylinder. This was needed to work around pushrods and head bolts. Not in the case of the ZZ632.

All eight of the ZZ632’s intake ports have the same length, volume, and layout. Similarly, the ZZ632’s exhaust ports are identical to each other. Speaking of volumes, we find 449 cc intake ports, 161 cc exhaust ports, and 70 cc combustion chambers. The valves are titanium, and measure 2.450/1.800-inches with 5/16-inch stems. The valve springs are a beehive style with a 1.589-inch diameter. One final note about the heads pertains to size. The heads are physically larger than any big-block head that came before it, so you will want to make sure you have plenty of room for them between the fenderwells of whatever you place it in.

Natural Aspirations

The single-plane intake (P/N 19366614) will surely cause issues for some, as hood clearance will probably be an issue with many cars. I couldn’t find any actual dimensions, but it places the included Dominator-sized throttle body (P/N 19366624) way up there. Also, the intake is a departure from convention as it incorporates a divorced valley plate that seals the top of the engine and supports the eight ignition coils.

The SFI-approved damper is installed and you can notice the crank trigger mounted in the timing cover that controls the firing of the eight coils mounted under the intake.

Yes, this engine comes with a self-learning EFI system. While the throttle body regulates the air intake, the eight 86 lb/hr port-mounted fuel injectors ensure sufficient fuel is fed to each cylinder. While some might think a larger injector could be beneficial to reduce the duty cycle, Alin has this to say, “the injector size was picked so that it would operate at around 90-percent duty cycle at its maximum demand. This delivers the best compromise between good fueling/atomization at idle/low-speed demands and full-throttle WOT demands.

“This is in line with GM’s best practices regarding injector sizing for port injected engines. Injectors operate best between 10- and 90-percent duty cycle. An injector that is sized too large may struggle to deliver stable fueling at idle conditions and is usually more expensive.” Finally, controlling the fuel and ignition is a pre-programmed engine control unit (ECU) to make the initial startup and all engine functions run smoothly. That means no laptop computer is required to tune the engine. In fact…

Unlike a traditional big-block, the ZZ632 uses an intake with a separate valley pan. The valley pan holds the eight coils and the intake seals to the heads via O-ring gaskets at each port.

“The engine can potentially make more power on race fuel, but ECU tuning would be required,” says Alin. “However, ECU tuning would void the warranty and GM recommends against this. The ECU is already tuned for maximum power from the factory and the risk of engine damage is high if performed. There is no additional power to be found through ECU tuning on 93 octane and again, GM recommends against trying.” That makes it sound like custom tuning is possible if race gas is used, but you do so at your own peril.

I also asked Alin if the dyno numbers were acquired using any special “thin” oils and he had this to say, “Mobil 1 0W-50 racing oil makes the best power, but the engine could also run on Mobil 1 20W-50.”

The final question I had for Alin was aimed at learning how much of this engine is derived from Mark IV, Mark V, or 8.1? He states, “the engine is primarily Gen-5/6. It does have a single-piece rear main seal with Gen-5/6 oil pan and timing cover bolt pattern.”

Get Shifty

Okay, short of a performance-oriented Turbo 400 transmission or a grab-your-own-gears four-speed, are there any electronic transmissions that will survive behind this behemoth and offer overdrive? Yes, actually, there are a couple. For starters, one could opt for the 4L80-E, but the size of that unit means some cutting of the floorboards will surely be needed. Another option is; Chevrolet Performance announced it has a new SuperMatic 4L75E-R four-speed automatic that can withstand the 876 lb-ft output of the 632 big-block delivers.

It takes a robust transmission to survive the abuse that 874 lb-ft of torque can deliver. Chevrolet Performance has that covered.

The 4L75E-R has a more compact design than the 4L80E. This makes it easier to fit within the transmission tunnels of more vehicles without any modifications. The 4L75E-R has a 3.06:1 first gear ratio, just as you’d expect from a transmission derived from a 700R4. That’s considerably lower than the 2.48:1 first gear ratio found in the 4L80-E, which should make for some neck-snapping launches. The 4L75E-R has a 0.75:1 overdrive to keep the engine humming at cruising speeds. If you do plan to run a manual transmission, the crankshaft is machined to accept a pilot bushing and the transmission input shaft.

The ZZ632 made a huge splash when it was released and now you can see what goes into making this tire-melting monster that we all want under the hood of almost anything we can think of. Chevrolet Performance has solidified the fact that performance is alive and well, and enthusiasts can rejoice knowing that horsepower is still a large focus of the General.