It all starts with a ZZ454 short-block (GM PN 12498778), purchased right over the counter
Building a big-block that's better in every way than the original Mark IV 427/435 is no small feat. But with the technology and high- performance parts that are currently available, it's not as difficult as you might expect. In this article, we'll show you everything you'll need to make this build as easy as possible.
As the saying goes, "It all starts with a good foundation." And the foundation for the original 427/435 was a four-bolt-main iron block with forged rods, pistons, and crankshaft. You can shop eBay and Craigslist for one of these blocks and then try to locate the correct complementary hardware. Even if you're able to do that, you'll still need to have everything machined, Magnafluxed, balanced, and generally reconditioned from top to bottom. When all is said and done, you'll spend a small fortune.
Laying the Groundwork
The plan we chose for our non-numbers-matching C3 should prove easier and much less expensive. We just went down to Jim Ellis Chevrolet and ordered a brand-new ZZ454 short-block. It's the latest, fully assembled, "Gen VI" version of the original iron big-block, and it comes with the same bulletproof four-bolt mains and a forged rotating assembly. Superior metallurgy and a modern forging process make this new block even stronger than the original, and the updated oil-pan gasket and rear main seal eliminate the usual leaks.
One of the keys to making big power is the ability to breathe. Getting the air and fuel in and out is critical. The original Mark IV 427 needed a solid-lifter cam, an 11:1 compression, and 100-octane leaded premium fuel to pump out the 435 horsepower. This new ZZ454, with the factory-installed aluminum heads, is rated at 440 hp right out of the box. With that as our baseline, we initially decided that 500 horses would be a good target. But, truth be told, that figure just isn't as impressive as it used to be.
AFR’s 265 Oval Port Aluminum Heads, shown with heavy-duty springs and titanium retainers,
In the hopes of obtaining even more power, we contacted Air Flow Research (AFR) to discuss our project. AFR recommended its aluminum 265 oval-port heads, which we ordered fully assembled with titanium retainers and heavy-duty valvesprings. The intake ports and combustion chambers were completely CNC'd, as were the bowls on the exhaust ports. The intake side on these heads flows 356 cfm at 0.600 lift, while the exhaust ports flow 270 cfm. That's comparable to the flow numbers on the latest Corvette's cutting- edge LS3 aluminum heads.
On our big-block, these AFRs will flow like Niagara Falls and deliver a high-velocity charge into the combustion chamber to make great torque throughout the powerband. AFR also milled the heads to increase our compression from the ZZ454's stock 9.7:1 to 10.25:1. Even so, we were assured that this motor would run on 91-octane unleaded pump gas all day long.
Since we were upgrading the heads, we decided to install a hotter camshaft as well. We weren't exactly sure what grind we needed, but we knew we wanted a hydraulic cam so we could avoid the frequent valve adjustments common to the original 427/435. The reduced friction and longer life expectancy of a hydraulic roller cam made it the ideal choice.
In spite of our 500-plus-hp target, this motor would be purely for street use. As such, it would need to develop enough vacuum for our power brake system and headlight actuators, and a reasonable idle would be nice, too. Finally, we want it to make power from 2,000 rpm all the way to 6,000 rpm for good driveability. In short, we wanted it all but weren't sure how to get it. Enter Lamar and Rob Walden.
AFR CNC’d the intake ports, the combustion chambers, and the bowls on the exhaust ports, a
The intake manifold was port-matched to the heads and smoothed all the way into the runner
Rob Walden checks the AFR heads’ flow numbers on his own SuperFlow SF600. They were spot-o