One-Upping Chevy: This N/A 632 Big-Block Makes 1,100 Horsepower

One-Upping Chevy: This N/A 632 Big-Block Makes 1,100 Horsepower

When Chevrolet Performance released the ZZ632 632 cubic-inch 1,000 horsepower crate engine, there really wasn’t much anyone could say other than, “Wow.” But, the ZZ632 is far from a perfect program — as the engine’s availability since launch is wait-list-only. And once you do have the beast in your possession, the factory ECU is locked out. So cracking into it voids the engine’s warranty.

Prestige Motorsports, in conjunction with Holley, have come up with an engine combination not only to match the orange monster, but surpass the bar it set by an easy 100 horsepower. All in a package consisting of readily available off-the-shelf parts that are easily tunable, unlike the ZZ632. Luckily, our friend Jeff Huneycutt of The Horsepower Monster was on hand to capture the build and testing of this awesome powerplant.

The massive 4.600-inch bores of this 632 aren’t even the maximum bore size for the World Merlin IV block. With its many features, the ability to make big cubes is chief among them.

The Monstrous Merlin Short-Block

For a bulletproof base, Prestige started with a rock-solid foundation; A World Products Merlin IV cast-iron block. This block can easily handle the intended 4.600 inches of bore and 4.750 inches of stroke needed to make 632 cubic inches of displacement, while maintaining enough strength to easily handle the 1,100-horsepower goal. Nestled into the block’s four-bolt nodular-iron main caps is a forged 4.750-inch SCAT crankshaft.

Clamped to the crankshaft is a set of forged 4340 steel Scat H-Beam connecting rods measuring 6.700 inches in length. Hanging off of the rods are a set of custom flat-top 4.600-inch forged 2618 RaceTec pistons with an extra short compression height to accommodate the extra rod length. When all is said and done, the pistons only sit in the hole .005 inch. King Engine Bearings’ pMax Kote coated bearings are used in both the rods and mains of this build.

A Moroso billet oil pump is used to provide crucial high-RPM oiling to this combination. The pump’s integrated pickup had to be custom-machined to work with the segmented high-volume Stef’s oil pan. Sealing up the bottom end proved to be slightly tricky with the massive stroke involved, and required notching of the oil pan gasket.

The 6.700-inch rod necessitated a short-compression height piston, putting the wrist pin into the oil ring land. The coated King rod and main bearings will keep the engine spinning smoothly for a lot of revolutions.

Big Power Needs Big Airflow

Like the ZZ632, this Prestige 632’s key to making power is in the massive cylinder heads. For this combination, Prestige opted for a set of AFR’s Magnum 18-degree big-block heads. With the relatively small (for a big-block) 90cc CNC-machined combustion chambers, compression should come in right at 13.2:1. The intake ports are CNC-machined as well, but are anything but small at 457cc of volume, flowing 498 cfm at 1.000-inch of valve lift. The exhaust ports are CNC-machined and measure 143cc, with an advertised flow of 342 cfm at the same lift.

Housed within the chambers are a 2.400-inch-diameter 11/32-inch stainless steel intake valve, and a 1.800-inch stainless exhaust valve, equipped with a 5-angle valve job. Controlling those valves are a set of PAC Racing triple valve springs, rated at up to 8,500 rpm and .900 inch of lift. They offer 385 pounds of seat pressure and up to 1,000 pounds of open pressure, and should be more than enough for this application. They are assembled with AFR’s 10-degree titanium retainers and bead lock valve keepers with lash caps.

The 90cc chambers aren’t large at all, by big-block standards. The volume, combined with the flat-top pistons make for a 13.2:1 compression ratio.

Controlling the movement of those valves is a custom solid roller camshaft from COMP Cams. It has a 4/7 firing order swap and features .797 inch of lift on the intake and .787 on the exhaust. At .050-inch of lift, the intake lobe has 280 degrees of duration, while the exhaust lobe has 298 degrees of duration, with a 112-degree lobe separation angle. A set of tie bar roller lifters translate cam motion into rocker motion, actuating the 1.7:1 T&D aluminum shaft rocker arms.

Topping Off The Big 632

It only seems fitting that Prestige chose the intake manifold designed specifically for the Magnum 18-degree heads – the AFR Magnum 18-degree single plane manifold. The manifold is designed to utilize a Dominator pattern carburetor, but this project is fuel injected, so Prestige welded on eight fuel injector bungs, and port-matched the intake’s mounting flange to perfectly match the Holley EFI Dominator-flange EFI throttle body.

The billet aluminum four-barrel throttle body will flow 2,000 cfm of air through the quartet of 2.250-inch bores, while providing the Holley Terminator X with a high-resolution throttle position signal. A set of Holley billet fuel rails house a set of eight Fuel Injector Clinic 1,200 cc/min fuel injectors. That should be enough injector to reach the target goal of 1.100 horsepower on E85, naturally aspirated.

The manifold AFR designed to match the Magnum 18-degree cylinder heads is designed for a Dominator-style carburetor. Nothing a few bungs and a little TIG welding from Prestige’s fabricators couldn’t fix.

Prestige outfitted the engine with one of Holley’s “Big Wire” coil-near-plug ignition kits, utilizing eight of Holley’s smart coils. An off-the-shelf Dual Sync distributor with the distributor portion blanked provides camshaft position information to the ECU. To control all of the timing and fueling of the engine, a standard Holley Terminator X ECU was utilized, as it is more than capable in this scenario.

After some initial break-in pulls, where the team dialed in the settings with some individual cylinder adjustments, and added a one-inch throttle body spacer, it was time to make full-boogie pulls on both race gas and E85. With the race gas, the numbers made were just over 1,000 horsepower. The real magic came with the E85. There, the engine made 1,106 horsepower (as was still climbing) at 6,500 rpm. Peak torque of 925 lb-ft was achieved at 5,600 rpm while torque never dropped below 780 lb-ft on the entire run. Not too shabby at all, for a naturally aspirated 632 big-block.

That’s one heckuva curve. 1,106 horsepower and 925 lb-ft of torque, with no less than 780 lb-ft throughout the whole pull. All from 632 naturally aspirated cubes on E85.

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About the author

Greg Acosta

Greg has spent nineteen years and counting in automotive publishing, with most of his work having a very technical focus. Always interested in how things work, he enjoys sharing his passion for automotive technology with the reader.
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