A pile driver is a mechanical device that smashes the earth with tremendous force, and the term is a fitting description of this 509ci street big-block Chevrolet unleashed by Outlaw Racing's Andy Mitchell. As our story goes, we had a 502 Chevy Ramjet engine liberated from Popular Hot Rodding's Project X, a fine engine combination from General Motors, replaced by an all-aluminum 427 in the latest incarnation of our heroic project car. We found ourselves in the enviable situation of having Project X completely renovated by the crew at GM with an all-new mill, while the old engine was hanging from a hook waiting for whatever our collective imaginations might conjure.
A 502 Chevrolet is not your standard production big-block, and its most distinguishing characteristic is the over-sized 4.470-inch bore. Production big-blocks were a full .220-inch less endowed in terms of bore size, and that big bore definitely provides an edge. A big bore provides a substantial displacement without the necessity of ungainly stroke increases. The formula here equals big cubes at moderate piston speeds, with less bore shrouding of the airflow into the engine. A big bore produces lower reciprocating assembly loads at high rpm than a similarly sized combination based upon a production block with its smaller bore. The block represented a substantial opportunity to unleash tremendous force, a potential that was just mildly exploited in the engine's original form. Our plans were to use the big-bore 502 block to build a high-powered street combination, a combination that could be accomplished with minimal effort.
We had big goals for the Pile...
We had big goals for the Pile Driver big-block: top 700 hp on pump gas, and do it with off-the-shelf parts. The only way to get there while staying naturally aspirated is with a solid roller cam, and deep-breathing induction components. Our search for the right heads and intake lead us to Trick Flow Specialties new PowerPort cyinder heads and R-Series single-plane intake.
With a 4.470-inch bore and a 4.00-inch stroke, a Chevrolet 502 is a big-bore combination relative to the stroke. It is an arrangement that is naturally suited to make strong power at higher rpm, and do so reliably, given the correct parts. In its original form, the Ramjet was configured to make tremendous torque in a mild engine combination. With conservative cam timing, moderate cylinder heads, a long-runner injected intake manifold, and a mild compression ratio, the engine produced low and midrange torque in abundance, with a peak of 565 lb-ft at a very low 3,200 rpm, along with its rated peak horsepower of 502 at 5,100 rpm. As much as we appreciate low-end torque, we had to wonder just what that big-bore engine could do if built to run up the rpm range.
Our strategy to tap into the higher rpm potential of the 502 involved nothing but the basics, using readily available aftermarket parts to add some heat to the combination. Sure, we would lose the dead-smooth idle quality of the original engine, but for a hot street machine it was a worthy trade for massive power gains through the mid and upper rpm range. The key areas of attention were the cylinder heads, cam, valvetrain, induction, and compression ratio. These are the parts that really determine the character of the engine. While the OEM combination was designed to produce a high vacuum, a dead-smooth idle, and a low-rpm torque, our new parts list was intended to produce serous power in the street/strip rpm range up to 6,500 rpm.
TFS Heads and Induction
Taking center stage in our upgrade were the new Trick Flow PowerPort heads for the big-block Chevrolet. These 320cc rectangular-port cylinder heads feature a 2.25/1.88-inch valve combination, 121cc chambers, and outstanding flow, with 360-plus cfm available at peak lift. With their ample size and flow, these cylinder heads are aimed squarely at the high-performance street and street/strip market, representing a substantial increase in capacity in comparison to the original oval-port Bow Tie GM heads, which are targeted more toward low-end torque.
A Chevrolet 502 short-block...
A Chevrolet 502 short-block is not your common big-block Chevy, as the big-bore block carries 4.470-inch bores as opposed to a maximum of 4.250 inches used in a production 454. These engines have been in aftermarket and marine applications for long enough that there is an ample supply of used units.
Our build plan for the bottom-end...
Our build plan for the bottom-end was to perform a basic rebuild of the short-block, punch the bores to 4.500-inch, and retain the original 4.00-inch stroke crank for a displacement of 509 cubes. Note the Gen-V big-block's one-piece rear main seal.
Filling out the fresh bores...
Filling out the fresh bores were a set of SRP 17cc domed pistons (front), replacing the 502's flat-top originals. The additional dome volume is required since we were going to replace the small-chamber oval port heads with Trick Flow's rectangular-port heads having a more typically sized 121cc chamber.