With multiple deck heights and bore sizes up to 4.600", the Big M Sportsman block gives you the versatility to build a wide variety of engine combinations for street, race or marine. Dart's maximum recommended bore and stroke allows displacements up to a massive 638 cubic inches (4.6125" x 4.75"). A true priority main oiling system oils the main bearings before the lifters for extra reliability.
- Standard 9.800" and tall 10.200" deck heights available for stroker engines.
- Standard 4.250" , 4.500", 4.560" or 4.600" bore sizes with siamesed extra thick cylinder walls to resist cracking and improve ring seal (minimum .300" thick with 4.625" bore).
- Uses +.300" tall Gen VI style lifters. Modification for Gen IV style available.
- Scalloped outer water jacket walls improve coolant flow around the cylinder barrels to equalize temperatures.
- 4 bolt main caps have splayed outer bolts for extra strength. (Big M = steel caps; Big M Sportsman = ductile iron caps)
- True priority main oil system lubricates the main bearings before the lifters. Our stepped main oil gallery (9/16" to 1/2" to 7/16") increases the flow of oil to the crank at high rpm, and our front oil crossover eliminates internal oil leaks around the distributor shaft.
- Oil filter pad is drilled and tapped for an external oil pump.
- Lifter valley head stud bosses prevent blown head gaskets.
- Rear main cap uses standard oil pump and two piece seal - no adapter required!
- Mechanical fuel pump boss, clutch linkage mounts, and side and front motor mounts simplify installation in any chassis.
- Dual oil pan bolt patterns fit standard and notched oil pans.
- Small bore 396 version available
- Parts kit: included for Big M; sold separately for Big M Sportsman
Do you have an extreme power build in mind? CGI Big M blocks can be special ordered. This Compacted Graphite Iron" technology doubles strength without added weight.
These blocks are available in any level of finish from ready for "as-produced" to fully machined to a complete custom crate engine. Whatever your needs, we can help.
Optional fully prepped block ready for assembly includes:
-Square deck to height and CNC chamfer cylinders on our 4-Axis Rottler CNC
-Deburr entire block & main caps
-Hone cylinders w/torque plate
-Align-hone mains, hone lifter bores
-Final clean block and paint with primer in your choice of colors
-Install cam bearings & test fit cam
-Install oil galley and freeze plugs
Our 4-axis CNC boasts precision of 0.0002" and one thousandth of a degree. Check out this Instagram time-lapse video of a probe cycle. While we do love our CNCs, we use old school stone hones for a finish we believe to be superior to that typical of diamond hones.
Pricing includes free standard shipping in the continental US.
Please call us at 815-725-2727 for questions and pricing on finish machining, short blocks, long blocks or full crate engines.
Buy your parts from people who use them!
While you are here, check out the video of a Big M build featured in Chevy Hardcore.
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