Pump Gas Monster: CNC Motorsports Builds a 582ci BBC Bottom End (PT 1)

May 24, 2018 / by Mike Magda

The big-block Chevy keeps getting bigger. Aftermarket blocks, dedicated stroker cranks, and array of piston sizes are pushing the good ol’ Rat to unprecedented stature–and horsepower.

CNC Motorsports, in Brookings, South Dakota, is no stranger to big-cube builds, offering several proven BBC combinations. However, when an overseas customer wanted an 800hp big block that would run on pump gas, they knew more cubes were the only answer. Using one of their proven 540ci big-block Chevy packages as a baseline, the shop spec’d out a 582ci version that would satisfy the low-maintenance, pump-gas requirement.

CNC Motorsports prepped the Dart Big M block with a Rottler F68a CNC machine, first by square decking the block and setting the deck height at 9.795-inch.
The lower structure need to be clearanced for the 4.375-inch-stroke crankshaft, so an end mill precisely adds clearance for the connecting rods.

“[The Customer] wanted a Pro Street-style engine for a ’57 Chevy pickup,” said Chris Carlson, a tech rep at CNC Motorsports. “He also wanted to keep it as a short-deck to avoid clearance issues, especially with the brake booster.”

The block was bored and torque-plate honed with vitrified-bond stones on a Sunnen CK10 machine to a final 4.600-inch diameter.
Here’s a close-up of the hone pattern and extra clearance for the rods. Note the chamfering on the bottoms of the cylinders.

Cramming 582ci into a short deck (9.800) deck height block is not a task for the faint of heart. It requires precise clearancing of the block and specially-designed stroker pistons that can survive the necessary 4.375in-stroke of a ride.

Before assembly, the block was painted black. The rear main seal and ACL main bearings are installed, then coated with assembly lube.
The K1 forged-steel, 4.375-stroke crankshaft is lowered into place in the block.
In addition to running on 95 octane, the customer didn’t want the hassle of adjusting valve lash on a solid cam. So, the next priority was a choosing a hydraulic roller for the large-displacement engine that would facilitate the 800hp goal.
A dab of black silicone helps seal the rear main cap area on the back of the block.
The bolts are lubricated before tightening down the main caps. Crankshaft thrust clearance was later verified at .007-inch.

The foundation was a standard-deck Dart Big M Sportsman block (PN 31273444) with a 4.500-inch bore. It featured a priority main oiling system and splayed 4-bolt main caps–both of which should be considered requirements in this level of build.

Inner and outer main cap bolts were torqued to 100 ft-lb in two steps: 50 and then 100.
All Total Seal rings were gapped checked with a feeler gauge, according to the manufacturer’s recommendations. For this application, the top compression ring was gapped at .021in, followed by .023in for the second ring.
Adjustments were made as needed on the ring filer to achieve the aforementioned gap specs.

The Dart block is not clearanced for some stroker crankshafts, including the 4.375in crank selected for this displacement, so CNC Motorsports used a Rottler CNC machine to square and surface the decks in relation to crankshaft centerline, as well as machine out material on the bottom side for clearance. The block was then bored out to 4.600-inch. Jon Himley at CNC Motorsports headed up engine assembly.

The K1 connecting rods are mated to the JE Pistons with a dab of assembly lube on the wrist pins and double spirolocks on either side of the wrist pins.
The Total Seal piston rings are installed on the pistons, with close attention paid to the clocking of the gaps.

The internally-balanced rotating assembly started with a K1 Technologies 4340 forged steel crankshaft (PN 012GAG438) that comes with a 4.375in stroke along with 2.749-inch mains and 2.200-inch rod journals. K1 also supplied forged 4340 H-beam connecting rods (PN 012AG33639). They measure 6.385-inch and are secured with ARP 7/16-inch, 12-point cap screws.

A lint-free rag and lacquer thinner is used to clean the bores in preparation for the pistons.
Assembly lube is applied to the connecting rod bearings, and the rod bolts are also lubricated.
A dedicated, tapered ring compressor helps ensure a easy installation, and that the piston rings are not damaged in the process.

Due to the massive bore, short deck height, and long crankshaft stroke, custom JE pistons were ordered with 6cc open-chamber-style domes to provide a 10.66:1 compression ratio. The full-round-skirt pistons are designed with a 1.218in compression height to accommodate the crank’s long arm. Sealing the bores is a Total Seal ring package (PN CRG4010-5) with .043-inch ductile iron plasma moly-coated top rings, .043 conventional second rings, and 3mm 3-piece oil rings.

More assembly lube is applied to the rod journals before the rod caps are torqued down.
The rod caps are hand tightened so deck clearance and side clearance can be double checked.

On the bottom end is a Melling high-volume oil pump (PN M77HV) fitted with a Kevko pickup (PN 1015) for use with the Kevko 6-quart steel oil pan (PN 1071). The pump is driven by an ARP driveshaft (PN 135-7901), and the pan is secured with a Manley hex-head, black-oxide-coated bolt kit (PN 42172) and a Victor Reinz cork gasket (PN OS30931XTC). Other finishing touches to the block include a fuel pump block-off plate (PN 839034) and oil filter adapter (PN 839049) from Pioneer.

The deck clearance checked in at .005-inch in the hole.
With deck clearance verified, the rods are torqued to spec.
Lastly, a feeler gauge verifies that rod side clearance is within spec after the rods are set.

Follow along as we detail the intricate assembly of the big-inch bottom end and stay tuned for part two where we assemble the top-end and run it on the engine dyno.


CNC Motorsports; 800-341-1528; Cnc-motorsports.com

JE Pistons; 714-898-9763; JEPistons.com

K1 Technologies; 440-497-3100; K1technologies.com

Brodix; 479-394-1075; Brodix.com

Dart Machinery; 248-362-1188; Dartheads.com


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Written by Mike Magda

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