The main webs are beefed up and fitted with steel 4-bolt main caps. Dart blocks are cast from premium high strength Iron with extra thick cylinder walls and decks. In fact, there are 15 new part numbers for the M 2 which are a direct result of customer input.Dart’s Iron blocks for Ford are designed to work with stock components, but are much more than a stock replacement.ĭesigned from the ground up for hard core racing, all the weaknesses of the factory castings have been addressed. The new Big M 2 offers a variety of options listed in an accompanying chart that outlines the available bore diameters and deck heights. This demands larger bore-diameters and perhaps a taller deck-height to satisfy the demand. Today, a big-inch street motor starts at 540ci and escalates the displacement from there. Now let’s get into some specifics with the Big M 2 blocks.
This also necessitates changes to the honing process used for cylinder-wall preparation compared to production blocks.Īn additional option for those operating on the maximum power side of things, is the option of choosing compacted-graphite iron (CGI) which offers even greater strength and hardness advantages over even the enhanced 32B iron. Note the use of the steel four-bolt main caps on all five journals of the Big M2, along with clearance pan rails that can accommodate 4.75-inch stroke applications on tall deckĪmong the reasons these blocks are so good is that they are cast using an enhanced 32B iron, which offers a higher 32,000 psi tensile strength rating, combined with a Brinell hardness rating of 207 to 255 compared to grey cast iron’s 187-241. Angling these outer bolts into a beefier portion of the block reduces the cap load distortion on main bearings. This main web cutaway (left) reveals the additional strength created through the use of a splayed outer main cap bolt. The piston thrust surface is the inboard side of the left (driver) side of the block with the outboard side as the major thrust surface for the right or passenger side of the block. The most important wall-thickness is always at the thrust side of each bank.
DART BLOCK PRO
Big-block foundations in either the Pro or Sportsman option deliver a 0.300-inch minimum figure at maximum bore size. But even at this point, the Dart M 2 blocks guarantee a wall thickness of 0.275-inch. Production bore spacing of 4.400-inch limits the largest bore size on a small-block Chevy to 4.185-inch. The deck height values stated in the charts will be delivered at roughly 0.005-inch taller than the stated value to allow room for minor machining to establish proper deck height with custom pistons.Ĭylinder wall-thickness is another major feature of Dart’s M 2 block lineup. This photo indicates the relative cylinder wall thickness on the outboard thrust side painted in red.ĭart M 2 blocks also feature thicker deck surfaces for increased overall strength. Plus, even with larger bore diameters like a big-block with a 4.625-inch bore, the cylinder wall will feature a minimum of 0.300-inch wall thickness. There are also other options such as raised cam locations and 55mm cam bore diameters.ĭart builds all of its M2 blocks with siamesed cylinder walls to allow larger bore diameters. Production blocks feed oil first to the lifter galleys from around the cam bearing and then down to the main bearings. Taller deck heights will accommodate longer stroke cranks for those big-inch builds.Īmong the many advantages of a Dart M2 block is its priority main oiling where a separate main galley from the oil pump feeds oil directly to the main bearing and then up to the lifter galleys.
Both versions are available in multiple bore diameters and deck heights. The main difference between these options is the Pro blocks are equipped with steel main caps while the Sportsman caps are ductile-iron. Both Dart blocks are available in either Sportsman or Pro versions. There’s more to these blocks than just a name change.īefore we get into the individual details, there are a few overall points worth investigating. But, one of the caveats of this horsepower escalation is that a casting that was happy at 400 horsepower may be the equivalent of quicksand when subjected to loads of 700 horsepower or more.ĭart Machinery has long understood these demands and recently upgraded its cast-iron blocks to what is now called the Little M 2 and the Big M 2. It’s no secret that we’re living in the golden age of horsepower. The engine builder’s equivalent of a solid foundation is nothing less than a quality cylinder block. The wiser man (who obviously is also a hot-rodder) built his house on a foundation of solid rock that survives the weather. There’s a parable in the bible about what happens to the foolish man who builds his house on a foundation of sand and is washed away in the rain and floods.
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