Building the Mark V engine was not unique, for the most part-a fairly straightforward assembly using Scat 6.385-inch 4340 H-beam connecting rods, Akerly & Childs Xtreme rings, and 4.5-inch-bore Keith Black hypereutectic aluminum pistons. The pistons feature a 1/16-inch top moly piston ring and a similar-sized cast-iron second ring. The pistons have a flat-top, making for excellent flame propagation, and when used with a 9.800-inch deck block they generate 10.25:1 compression. An Eagle forged steel crankshaft was used with a 4.250-inch stroke, making for 532-cid total displacement (540 cid for you government workers)
The cylinder heads were state-of-the-art RHS Pro Action 360cc aluminum heads. The heads started plenty clean from the factory with excellent airflow and internal water jacketing for consistent temperature control, and were ported to the next level by Toby Allison. Because of the high horsepower Jim wanted to generate, he felt a Toby porting job would help eek out the engine's top horsepower numbers.
In the valvetrain department, Shewbert clearly wanted a big camshaft to take advantage of the high-flow cylinder heads, horsepower, and torque-handling attributes of the super-strong Mark V short-block (see the CamQuest 6 sidebar). To that end, he selected a camshaft that featured large lift and duration numbers requiring a mechanical roller valvetrain, which included COMP's new Endure-X mechanical roller lifters. In combination with the big camshaft, the COMP Cams tech line folks (800/999-0853) helped him select appropriate valvesprings, retainers, lifters, spring cups, lash caps, and even the Pro Magnum roller rockers used with this combination.
Topping the engine was a Dart intake ported by Allison and a Demon-reworked 850-cfm carburetor. Big-tube exhaust headers and low-restriction Flowmaster tailpipes were slated for use, along with a five-speed manual transmission and high-performance clutch.
On To The Dyno
The folks at Westech Performance were hired to test the limits of our engine. Engine builder Jim Shewbert installed the camshaft with four degrees of advance, along with the Dart intake, Demon 850-cfm carburetor, and MSD ignition. Using 91-octane fuel, Westech's Steve Brule fired the engine and spent a considerable amount of time warming the engine, then resetting the valves and warming the engine again with some short low-rpm pulls. After an hour of break-in time, they proceeded to make some test runs to see if we had done the proper homework.
The Mark V required a few jetting changes, and we adjusted the timing slightly during our four test pulls. In the end, our 540-cid Mark V big-block turned out an impressive 649.2hp at 6,200 rpm and 613 lb-ft of torque at 4,900 rpm. The most impressive part of the engine's power and torque output was the consistent power delivery. From 5,700 through 6,700 rpm, the engine maintained a minimum of 640hp-less than a 10hp variance for over 1,000 rpm. In addition, the torque level reached 590 lb-ft of torque starting at 4,100 rpm, and stayed above that level through 5,700 rpm. This is usable street horsepower that would be more than up to any race challenge encountered by the classic Chevelle.
Shewbert likes to run Manley stainless steel valves for all his engines. These measure 2.2
Toby Allison reworked the entire length of the ports and valve bowls....
...The RHS Pro Action cylinder heads work great from the factory and run well without modi