One horsepower per cubic inch. Back in the 1950s, that was the target. Those newfangled overhead pushrod engines that revolutionized how passenger car engines were created only served to heat up the power-per-cube race. When the new Chevrolet big-block engine was introduced in 1965, it lit the fuse for bigger power and renewed the focus on the power-per-cubic-inch wars.
Today, making big horsepower is still the ultimate goal; the one-horsepower-per-one-cube-of-displacement target is but a mere dot in the rearview mirror of old aspirations. But complications to the engine-building process have surfaced recently. For many builders, the engines they create must make excellent power and still be compatible with today's low-quality pump gas (91-octane). In addition, they must be able to generate adequate vacuum and excellent daily-use drivability. Just as today's performance cars are compatible with formerly antiperformance style options, such as A/C and power steering, most current engines don't need 114-octane race fuel to avoid detonation while hitting the big power figures. The fact is no engine builder wants to tell his clients their freshly built engines require such coddling. Why should they when proper component selection will help them avoid such behavior?
A Little Big-Block History
The big-block Chevy engines of today come in a variety of shapes and styles. While the Mark IV, introduced in '65, went through some initial changes, it was not until '91 that the Mark V engine came to be. Today, the Mark V and its brother, the Mark VI, which debuted in '96, are good platforms for engine builders, offering great versatility and availability over the seemingly harder-to-find Mark IV engines. Featuring strong internal webbing, an integrated oil pan gasket, and a one-piece round rear main seal to avoid oil pan drips, the Mark V was perfect for our needs. Paired with the hot-performing RHS Pro Action aluminum cylinder heads, we were excited about the potential for what we believed would be an excellent combination for our street-based project.
The selection of the Mark V platform was the work of engine builder Jim Shewbert, who was hired to create the potent big-cube engine for Ted Yurek's '70 Chevelle. The car, while outfitted with a number of advanced suspension upgrades, was a true dual-purpose machine; both track and cruise time were planned for the beautiful blue-and-SS-stripe-clad heavy Chevy. While the engine was assembled in Southern California, the Chevelle was expected to run on pump gas once dropped between the inner fenderwells of the Coeur d'Alene, Idaho-based Chevy. Owing to the huge amount of distance between L.A. and Idaho, it was imperative that the engine be powerful and reliable.
 A man of many engines, Jim...  A man of many engines, Jim Shewbert has been building and racing engines, including anything from alcohol Funny Cars to Pebble Beach Concour-winning multimillion-dollar classics, for 35 years. The challenge this time-building a streetable 540-cid Mark V big-block Chevy that could run on pump gas and make over 600hp. |  The Mark V big-block requires...  The Mark V big-block requires oil-system bypass valves to make it compatible with an engine-mounted oil filter system.... |  ...Forget these bypass valves...  ...Forget these bypass valves and you can kiss your engine goodbye, as oil will not circulate properly through the engine. And don't forget that threaded plug that fits in the oil-pan rail, as shown here. |