Bare, cast iron, competition blocks are precisely machined, with four bolt, nodular iron main caps, tall lifter bores and extra smooth gasketsurfaces for superior sealing. Features: 350 Main, 400 Bore Size Bowtie Sportsman Block2-Piece Rear Main SealCNC-machined cast iron competition block+/-0. 001 machining tolerances4-bolt nodular mains, splayed caps on center 3 mains4. 117 finished bore4. 155 max bore (siamese cylinder bores)Extra smooth gasket surfaces for better sealTall lifter boresPit Stop USA offers GM Performance Parts Bowtie Sportsman Block - 350 Main, 4.125" Bore 12480157 at low everyday prices. Be sure to check out all of our products from GM Performance Parts including GM Performance Parts Cast Iron Engine Blocks - Small Block Chevy.