The 454ci big block Chevy engine was first produced in 1970 by lengthening the stroke of the 427ci BBC engine from 3.76- to 4.00-inches, while maintaining the same 4.25-inch cylinder diameter. Performance enthusiasts and engine builders have taken that increase several steps further since, including increasing the displacement to 496ci. This stroker combination is achieved by increasing the factory bore to 4.31-inches and installing a 4.25-inch stroke crankshaft. This combination is not to be confused with GMs late-model production 8.1L Vortec engine that also had a displacement of 496ci. The 8.1L uses a different bore and stroke, and is a low-performance truck engine.
Locate a serviceable 454ci engine. Completely disassemble the engine. The original crankshaft, pistons and connecting rods will not be used, but the remaining components will be. If reusing the original cylinder heads, take the heads and engine block to a reputable machine shop for cleaning, inspection and machine work.
Order a 496ci rotating assembly. These kits include the longer-stroke crankshaft, larger-diameter pistons and longer connecting rods. Many rotating kits include rings and bearing inserts, as well. Be certain to specify the proper type of crankshaft balance to be used -- internally or externally balanced. Factory 454 engines use external balancing weights on the harmonic balancer and flywheel. If using a kit that is internally balanced, non-balanced flywheels and harmonic balancers are required.
Instruct the machinist to check the alignment of the main bearing bores and machine to specified tolerances, if needed. It's also a good idea to have the cylinder block deck machined so that it's surface is flat and square relative to the crankshaft centerline. Have the cylinder bores of the block increased to a diameter of 4.31-inches. The machinist will need the pistons to properly fit them to the cylinder bores. It's recommended that the machinist check all measurements of the crankshaft and rods to ensure that they are correct, as well. Balancing the entire rotating assembly is suggested, but not required unless severely out of recommended tolerances.
Have the cylinder heads cleaned and reconditioned with a performance valve job. If they are to be used in a standard-performance application -- such as a tow truck -- the original 454 heads will perform well. If this is a high-performance build, the heads should be ported and modified to meet the increased airflow requirements of the larger displacement. Alternately, new aftermarket heads can be selected that are more suitable, and may be justified in light of the extra machining and labor costs required to modify the factory 454 castings.
Assemble the engine according the engine-building manual, taking care to follow all clearance-measuring and fastener-tightening values.
