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Part number: 31512323
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Product Details
Dart 31512323 4.5 Bore Spacing Block
Products specifications
Cyl Bore 4.18in
Deck 9.325in
4.5" Bore Spacing Iron Chevy Small Block
400 Mains

By spreading the cylinder bore centerlines from the standard 4.400 to 4.500, large bore sizes can be achieved with adequate head gasket sealing space between the cylinders.

Bosses are added at the ends of the decks to accommodate two extra head studs, increasing clamping loads and improving gasket sealing. (The extra studs are also provided for in Darts new 4.500 bore space cylinder heads). These new blocks are ideal for big inch competition engines. The cam location is raised .391 and oil pan rails are spread .400 per side on both the iron and aluminum blocks, providing lots of room for stroker crankshafts while eliminating the need for fragile small base circle camshafts. Big block cam bearing journals are standard, and 350 or 400 main bearings are available.

It is recommended that you contact a Dart technical representative before placing an order for this item. Detailed information about your planned engine build will help to ensure that you choose the right configuration for your motor and that any special parts and considerations are taken into account.


  • 8.850, 9.025, 9.075, 9.325 and 9.500 deck heights allow for greater versatility.
  • 4.500 bore spacing comes with 4.180 bore size standard, larger bores available on request, please call.
  • Raised camshaft .391 (4.912 camshaft to crankshaft centerlines) provides more clearance for stroker cranks and eliminates need for fragile small base circle cams. Option for .434 raised cam also available.
  • Relocated oil pan rails are spread .400 per side (.800 wider than stock) to increase crank/rod clearance and reduce windage losses.
  • Oil pan bolt holes are relocated in line with main caps to eliminate interference with rotating assembly.
  • Main bearing bores are available for 350 (2.45) and 400 (2.65) bearings allow engine builders to maximize crankshaft strength and minimize friction.
  • 4 bolt billet steel main caps have splayed outer bolts minimize bearing bore distortion.
  • Big block camshaft bearings allow use of cams with larger base circle diameter to improve strength and recue twisting with cam driven pumps.
  • Dual starter mounts allow starter to be mounted on either side of block for chassis and oil pan clearance.
  • Front and rear external oil inlets, crossover and restrictor provisions to simplify plumbing with external pump.
  • Scalloped outer water jacket walls improve coolant flow around the cylinder barrels to equalize temperatures.
  • Coated cam bearings, freeze plugs and dowels are included.
  • Dart blocks are available fully finish prepped.
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Best prices I could find anywhere! Fast shipping. Will definitley buy from again.
Hard to find part, in stock, and the best price around.  Amazing!!!
Product delivered as expected within 4 days.  Lowest price on the web.  No complaints.
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