The 496 cubic-inch big-block Chevy (BBC) was one of the earliest BBC "stroker" engines designed by performance enthusiasts with combinations of both existing and aftermarket parts. Its displacement is achieved by using an aftermarket crankshaft that is .25 inch longer than standard, along with a cylinder bore that is increased .060-inch. The bore/stroke specs are 4.31 and 4.24-inches, respectively. Even though much larger stroker engines are possible, this displacement is about as large a combination as can be achieved with the factory 454 cylinder block. With careful machining and fitting procedures and parts selection, the 496 BBC can make well over 750 horsepower in competition form.
Things You'll Need
- 454 CI Chevy donor/core engine
- 496 CI stroker rotating assembly
- Aftermarket performance components (optional)
- BBC performance engine assembly manual
Planning, Parts Sourcing and Dis-assembly
Plan the build. Locate a suitable core or donor engine. Salvage yards are a good source. The 454 was introduced in 1970. The earlier engines, known as Mark IV BBCs, were more desirable than some later ones, and were produced until 1991.
Order a stroker crankshaft and kit that is suitable for the intended operation of the engine. A 496 that will see severe usage should be built with premium components, such as a forged crankshaft and connecting rods, and forged aluminum pistons.
Purchase aftermarket performance cylinder heads, as well, in order to achieve optimum output from the increased displacement. Select a camshaft and the remaining induction parts -- intake manifold and carburetor -- to complete the engine. These parts must be oriented and compatible with the heads and intended use of the engine.
Disassemble the core engine. Sell the old crankshaft, rods and pistons, as well as the old heads to offset the expense of the new components.
Machining and Re-assembly
Take the engine block and new rotating assembly to an engine machine shop. Provide the machinist with the details required to prepare/blueprint the engine block. Common procedures include align-boring/honing the main bearing bores, surfacing the cylinder block decks to the proper height and boring and honing the cylinders to the proper diameter. The new pistons are required for the machinist to complete this last item.
Balance the rotating assembly -- crank, rods and pistons. This is critical. It ensures that there are no potentially destructive harmonic vibrations that could cause engine failure. One alternative is to have the engine machinist assemble the entire shortblock; this could save time and expense, plus it will result in professional assembly.
Provide the machinist with the old heads to be reconditioned with a performance valve job and upgraded performance valve springs. If new aftermarket heads are being used, they may already have the proper springs for a performance camshaft, but it is wise to have the heads double checked anyway.
Assemble the engine according to the instructions in the performance engine building manual. Pay particular attention to clearances and tightening specs for all fasteners.
Tips & Warnings
- This combination is not to be confused with the GM 8.1L Vortec, which also had a factory displacement of 496 CI. That engine used much a different block and heads, and was not suitable for a performance build.
- Always use the correct harmonic balancer and flexplate for the intended type of crankshaft balance: internal or external.
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