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350 Main Bowtie Sportsman Block, 2-Piece Rear Main Seal

Brand: Chevrolet Performance

Part Number: 12480047




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4-Bolt 350 Main Block


Bowtie Sportsman Blocks

Step up to serious street/strip performance when you choose a Chevrolet Performance Sportsman Block. These iron blocks provide a rock-solid foundation for any application in the 350 – 500-horsepower range, be it drag strip, circle track or high performance street machine. These highly versatile blocks are available in a variety of finish options that enable maximum flexibility for building a wide range of engine combos. Most of the blocks have siamesed cylinder walls and 4-bolt main caps that are secured with Grade-8 bolts. Chevrolet Performance Bowtie Sportsman Blocks have 9.025-inch deck heights.


12480047 Chevrolet Cylinder Block

350 Bowtie Sportsman Block, 2-Piece Rear Main Seal

  • CNC-machined cast-iron competition block
  • +/-0.001" machining tolerances
  • 4-bolt nodular mains, splayed caps on center 3 mains
  • 3.980" finished bore
  • 4.155" max bore (siamesed cylinder bores
  • Extra-smooth gasket surfaces for better seal
  • Tall lifter bores

Bowtie Sportsman Block Technical Notes:

  • Standard 9.025-inch deck height
  • Nominal cylinder wall thickness is 0.340-inch
  • Minimum cylinder wall bore thickness on 4.155-inch bore is 0.225-inches (excluding P/N 10051181, 10051183, and 10185047)
  • Extra-thick deck surfaces have blind-tapped bolt holes for improved head gasket sealing
  • Priority main oiling system
  • Main bearing bulkheads are 0.900-inch thick and use Grade-8 bolts
  • All five cam bearing locations require 2.000-inch O.D. (1.867-inch I.D.) bearings P/N 12370843 (except block P/N 10051183)
  • Tall lifter bore blocks may require clearancing the top of the lifter bores for some roller lifters
  • Lifter valley oil scavenging boss below bell housing flange is present, but not drilled and tapped
  • Oil dipstick holes are not drilled
  • Timing system clearance must be checked

Notes: Bowtie blocks are called out by main journal sizes (i.e., 283, 350 or 400) and then by bore size (i.e., 283, 305, 350 or 400) if the bore is not standard to the main size. Example: P/N 24502650 – “283 Main-350 Bore size”– has standard 283 main journal sizes; however the bore is standard 350 size.

Siamesed cylinder walls have thicker cylinder wall material with no water between the bores. This allows for a bigger bore; a bigger bore allows for more cubic inches and more power!

4-bolt mains have more material and more fasteners holding the crank in the block (4-bolts per main instead of just 2). 4-bolt mains help maintain the integrity of the block when you drop the hammer!