Billet Crankshaft Billet 4340 Steel
Product Discontinued
MOPAR PERFORMANCEPART NUMBER: 312-P5007903

Billet Crankshaft Billet 4340 Steel

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This product is no longer available. Please call customer service for assistance at 1-800-345-4545.

Crankshafts
    Billet Crankshaft
  • Billet 4340 Steel
  • 3.80" Stroke
  • 318/340 Main Journals
  • 2.000" Rod Journals (Use w/ SBC Small Journal Rod Bearings)
  • 6-Bolt GM Rear Flange (Fits Standard Sprint Car U-Joint)

Normally used in 410ci Sprint Cars and Dirt Late Models, the Mopar A8 is an aluminum small block racing engine. It must be used with a dry sump oiling system and the gear drive systems shown below.

Show More A8 Aluminum Block Features
  • Full Bell-Housing
  • Siamese Bore Casting, 318/340 Mains
  • Ductile Iron Cylinder Sleeves with 4.120" Rough Bore
  • 4-Bolt Billet Steel Main Caps (Center 3-Caps)

Mopar’s A8 Aluminum Blocks & Components line is built for racers and performance builders who want maximum strength, reduced weight, and serious displacement in their Mopar platform. Whether you're chasing low ETs on the strip or competing in sprint car classes, this range offers a foundation that’s tough, precise, and race-ready.

The A8 blocks are cast from high-grade A356 aluminium and fully CNC machined, giving you an aluminium engine block that delivers outstanding thermal properties and lighter mass up front. With steel billet main caps, including a four-bolt, splayed design on the center three caps, these blocks stand up to punishing loads, high rpm, and aggressive camshaft profiles. Deck heights range from approximately 9.015” to 9.435”, and bore sizes go up to 4.180” to support large displacement builds.

Designed to pair with W9 or W9RP cylinder heads, the A8 line also retains compatibility with Mopar 340 mains and crankshaft spacing, allowing proven components to carry over. The block’s internal layout features optimized valve train geometry, relocated tappet bores, and sleeves engineered to endure extreme service. A dry-sump oiling system is standard, making these blocks built for serious motors.

If you’re comparing platforms, this isn’t an audi w12 engine block style design. The A8 is all about Mopar performance heritage, closer in spirit to the legendary 340 block but engineered with modern materials and technology for today’s racing demands.

In short: the A8 Aluminum Blocks deliver displacement potential, durability, and cutting-edge design so you can focus on winning. Add one to your build and lay the foundation for power.

Part TypeCrankshaft
Product LineMopar Performance A8 Aluminum Blocks & Components
BrandMOPAR PERFORMANCE
Part CategoryPerformance Parts
Crankshaft MaterialBillet steel
Rod Journal Diameter2 in (50.8 mm)
Main Journal Diameter2.5 in (63.5 mm)
LightenedYes
QuantitySold individually
Crankshaft Snout StyleStandard
Main Bearings IncludedNo
Engine BalanceInternal
Rod Bearings IncludedNo
Rear Main Seal Style2-piece
Requires Narrow BearingsYes
Engine Stroke3.8 in (96.52 mm)
Vendor Part NumberP5007903
Package Qty1
Package TypeEA
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