GM Performance Engine Block, Cast Iron, 4-Bolt Mains, 4.494 in. Diameter Bore, 1-Piece Rear Main Seal, Chevy, Big Block, Each (PART #GMP-25534364)

GM Performance Bowtie big block Chevy cast iron engine blocks are CNC-machined. The race-prepared blocks feature blind head and accessory mounting bolt holes, a deck configuration that enables the use of any big block Chevy cylinder headaand cylinder bores that may be safely bored to a 4.600 in. maximum diameter, while maintaining a .250 in. minimum cylinder wall thickness. These engine blocks differ from the production-machined Bowtie versions in certain areas; they start from raw castings and are not "conversions." They also use a rear seal adapter to convert the Gen V/VI one-piece rear main seal to a Mark IV type 2-piece seal that facilitates the use of a widely available Mark IV style crankshaft.

The intermediate caps also feature 16 splayed outer bolts, which anchor the caps into the strongest section of the blocks and prevent bearing cap movement under high loads. The main oil gallery on these blocks is relocated and enlarged to a 9/16 in. diameter to allow increased oil flow through the block. These Bowtie blocks have inner head bolt bosses, which allow for better retention of the cylinder heads in high-horsepower applications when the cylinder heads "lift" from the blocks due to high cylinder pressures. Order the style and deck height preferred for your application.