Rarely did the street urchins gather before midnight in the dark corner of the mall parking lot; their surreptitious activities waited patiently until then for the streets to clear out and tarmac trawlers to make their rounds. Suddenly, a sinister black Camaro made its presence known, and all heads swiveled in unison as it cruised past the small group. Prior to making its debut on this evening, the Camaro had been unknown, so naturally this crowd was eager for a closer look at the newcomer, and to find out if it was a player… or a poser.
It certainly seemed the part of a serious contender: The barely muffled exhaust did little to conceal a hard-hitting cam, Lakewood slapper bars were appropriately attached to the rear leaf springs, and the sticky street slicks on vintage 10-inch Centerlines tucked themselves neatly inside the quarters. As the driver’s door swung open, a lanky driver in his early 20s emerged, whose long, greasy hair matched the grease permanently embedded under his fingernails. Immediately and to the point, the clique began the expected interrogation. Among the group there existed a couple of heavy hitters who dominated the local boulevards; everyone wanted to know what the Camaro’s game was.
The Camaro’s wheel man wasn’t shy about letting it be known that he was looking for a little competition; something that would either validate or discredit the time, effort, and expense he’d lavished on the F-body.
“Whatcha runnin’?” they all wanted to know. The mystery man lifted the hood to expose the object of their curiosity. “It’s just an old 396 I had lying around. I punched it 30, and finished it with a cam, intake, and Holley carb,” he conceded. Eyebrows were already being raised in suspicion at the recounting. The headers and Accel ignition pieces were other obvious additions, and typical of the performance hardware of the day. Inside the Camaro, a Hurst shifter actuated the Muncie four-speed, while a Sun tach was augmented by a full brace of Stewart Warner gauges. A pair of lightweight plastic buckets replaced the heavy vinyl-clad stockers, lending credence to the notion that the Camaro was ready to take on any challengers. Clearly, the night would not end without someone defending the honor of the group. The question was… which one would it be?
Similar scenarios have played out innumerable times across the country, as scores were settled on remote back streets and the current baron of the boulevards was determined. Perhaps you were a willing participant of the game at some time or another and might have even been crowned the king. Sure, the bragging rights were all yours… until the next mystery challenger showed up.
The success of enticing the next victim is owed significantly to one’s ability to deceive the competition. Each one of us, at one time or another has engaged in a willful charade. In automotive circles they are often found in the form of verbal fabrication, exaggeration, omission, or out-right lies. Pick one. They all work, depending on the circumstance. The most effective, however, might just be the untruth of omission, where something in question has the appearance of something it really ain’t. So, what do you think? It’s a fair bet that the high-octane bunch in our scenario above wondered among themselves whether the claimed “396” was actually more than what met the eye.
Photo: Chuck Hanson
The big-block Chevy buildup chronicled here is a great case in point. To the untrained eye, it appears to be a nice “Day 2” engine, with an unassuming, mostly stock appearance. Except for an aftermarket intake and carb, plus a few ignition enhancements, it could have been found under the hood of most any Bowtie street runner from the late-Sixties right up to present day. Throw on a couple of 396 air-cleaner decals and the deception is nearly complete. What this innocuous appearing Rat conceals, however, is 496 cubic inches of high-compression, high-tech packaging that cranks out an astounding 726 horsepower and more than 650 foot-pounds of grunt! If our friend in the stealth Camaro was packin’ that kind of heat, chances are the clique’s representative went home disappointed that night.
The right visual clues are essential to promoting this kind of ruse. Flashy, go-fast parts and power adders on the outside might up the performance game considerably, but they also tip off the opposition. And as we all know, it’s what’s on the inside that really counts anyway. A lowly two-bolt-main 454 provided the foundation for this buildup, and the block’s “512” casting numerology gave credence to its late-’60s/early-’70s assembly-line origins. The heads, too, were pedestrian “990” cast-iron lumps that featured rectangular ports, 118-cc combustion chambers, and 2.19/1.88-inch valves right out of the box. Topping them with factory chrome steel valve covers complete the guise of originality.
Bolted between the heads is a vintage Weiand X-CELerator intake; it’s an efficient single-plane design that allows the observer to conclude it’s nothing special, while the Holley double-pumper it supports is similar in nature. Externally, there’s very little to arouse the suspicions of the street jousters, and finding a willing accomplice for a late-night tussle should be an easy undertaking. And, since all Chevy big-blocks are nearly identical externally, concealing the added displacement is just as easy.
Achieving a 496-inch displacement requires a 4.310-inch bore and a 4.250-inch stroke, and the 454’s block easily accommodates both. But there’s more than larger displacement required to generate upwards of 720 horsepower; both cam and compression require serious upgrades, while the iron heads mandate increased airflow numbers to work in holistic compatibility with the rest of the componentry.
In the past we’ve enjoyed tremendous success using the expertise and capabilities of Tommy’s Auto Machine in Springfield, Tennessee, so it should come as no surprise that we entrusted them once again with the machine work, assembly and testing of this big-inch thumper. This big-block will eventually be strapped between the fenders of an early-’70s Chevelle, with an owner who plans to deploy it on the streets and “just have fun with it!” As you might expect, it swills only 110-octane race fuel, and does so at a phenomenal rate of consumption. But it’s nearly guaranteed that the “fun” will be mostly one-sided as the contenders step up, and then step aside as they are dispatched with unsurprising regularity. Stay with us now as we reveal what it takes to assemble a surreptitious Chevy that’s deliberately deceptive and unusually competitive. After all, it’s “just a 396 with a cam, intake and carb.”
726-HP 496-cu.in. Chevrolet – Engine Build
Meticulous machine work on the 496-cu.in. big-block included squaring and decking the block before cinching down the torque plates and boring it .060-inch over to 4.310 inches.
Once the block was squared away, splayed billet, four-bolt main caps were torqued in place, and the mains were align-honed. The Molnar crank is forged from 4340 steel alloy, then treated to nitrided main and rod journals, indexed, and given a multi-stage heat treatment to ensure reliability and longevity. ARP studs and bolts secure the bottom end.
Molnar H-beam rods accommodate floating piston pins on the small end, and measure 6.365-inch to work with the Ross pistons. Monstrous 50-cc domes put the squeeze factor at 13.7:1 with 120-cc open-chamber heads. Total Seal gapless rings ensure maximum cylinder sealing for more power, and are configured in a standard 1/16-, 1/16-, 3/16-inch ring pack.
A tapered ring compressor from ARP makes quick work of the piston installation, allowing them to be gently tapped into place while ensuring the rings are properly compressed and undamaged.
With the rotating assembly in place, crank thrust is checked at .003 inch, while the ARP fasteners are torqued down to 110 ft-lb on the inner studs, and 80 ft-lb on the outer bolts. The cap screws on the Molnar rods are cinched down to 85 ft-lb, with bearing clearance on the mains set at .003 inch and the rods at .0033 inch.
After securing the Melling standard-pressure/standard-volume oil pump, the bottom side was buttoned up with an original GM big-block oil pan. A Fel-Pro one-piece oil pan gasket makes sure the engine’s lifeblood stays where it belongs.
At the heart of this brutish big-block is a Bullet hydraulic roller camshaft that specs out at 274/282 degrees of duration on the intake/exhaust respectively, while the valves are moved .739/.725-inch off their respective seats. Isky roller lifters transfer the motion to thick-wall (.090-inch) pushrods measuring 9.350 and 8.250 inches in length.
It pays to check the cam card and be extra careful when installing any camshaft of considerable dimensions. Improper valve-to-piston clearances can cause the engine to make unwanted, expensive noises. The Bullet cam was installed “straight up.”
The cam card indicated an intake centerline of 107 degrees, and the degree wheel validated that number. The Cloyes billet roller timing set provides multiple keyways for cam timing variations, so the lower gear was marked to indicate the proper alignment with the upper gear’s “dot.”
A Fel-Pro #17046 Kevlar-reinforced head gasket was entrusted to contain the combustion process and features a 4.370-inch bore and a .039-inch compressed thickness.
Once the iron “990” head castings were appropriately enhanced (see sidebar, “PORT-a-POWER”), they were laid in place and attached with ARP bolts, cinched down in three increments to 70 ft-lb. The threads are coated with sealant to prevent leakage where bolts project into the water jackets; ARP assembly lube under the bolt heads will assure accurate torque readings.
After the camshaft was lubed and slid into place, the Isky “Red Zone” hydraulic roller lifters were thoroughly doused with assembly lube before dispatching them to the lifter valley. Painting the valley surface facilitates oil return to the pan to help ensure a constant supply of the engine’s lifeblood.
The sheetmetal pan in the lifter valley is a GM piece originally installed on the 427 L-88 big-blocks and was intended to keep the bottom of the intake manifold isolated from hot oil. Fel-Pro Printoseal intake gaskets feature elastomeric beads around each intake port to promote a solid seal between the heads and intake.
Responsibility for transferring motion from the pushrods to the valves was assigned to a set of Crower 1.7:1 ratio stainless steel roller rockers. Their beefy design and oversized trunnions will maintain accurate valve timing with long-lasting reliability.
The vintage Weiand X-Celerator intake has an innocuous appearance, although its single-plane design allows surprising air delivery for proper care and feeding of the voracious Rat. A heavily reworked AED/Holley double-pumper tops the intake, providing a substantial increase in fuel and airflow over its original 850-cm configuration, while an MSD ignition lights the fire.
Stock Trader
The owner of this 496 was adamant that the mechanical ruse was as undetectable as possible. Towards that end, a slew of original factory parts was utilized to minimize detection and increase the possibility of luring another victim. For instance, the “512” block is quite desirable with the restoration crowd. Expensive yes, but it served well here to confirm the era and application. Likewise, the rocker covers, oil pan, harmonic balancer, and timing cover are all endemic to factory engines installed during the late-’60s/early-’70s. Pristine, suitable components were located after hours of on-line scouring, and came with a wallet-flattening price tag. What price deception, indeed!
The evasive (and pricy) “512” block is immensely popular with the matching-numbers resto crowd, and the casting number is found on the passenger-side, top of the bellhousing flange. While expensive, it was a necessary component that provided the foundation for the stealthy big-block.
Stock Trader
After finding a pristine pair of factory chrome rocker covers, the integral “drippers” had to be trimmed to clear the roller rockers. Outwardly, they still looked original with the chrome and dripper spot-welds still intact, but lovers of originality would still decry the outrageous act.
Stock Trader
Finding an NOS or undamaged original factory oil pan proved to be quite a challenge. Eventually an unmolested original was located; it features the double layers of internal baffling to help minimize oil slosh during extreme engine events.
Stock Trader
Although an 8-inch balancer would not be found on a factory two-bolt-main engine, it is worth the compromise according to the owner, and was complemented by an original timing cover with the correct “flat” AOR timing tab.
Stock Trader
The crank and water pump pulleys are also era-correct, factory hi-po deep-groove items, designed to keep the drive belts in place during high-speed engine operation.
Power Play
Although this engine build is based largely on the art of deception, the dynamometer is the ultimate truth teller. So, we strapped it to the Superflow dyno to test its mettle and learned that the beguiling big-block performed much as we expected. We may have left a little power on the table by using the retro intake, which created a bit of a bottleneck in the intake tract. A more contemporary casting could have added another 20-30 horsepower, but the design would have detracted from the vintage Day 2 vibe the owner was hoping would work to his advantage. Take a look.
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