For the ultimate in small-block durability, Dart has two options: the Little M and the Iron Eagle blocks. The Little M is a true race block that is cast from a premium high-strength alloy and is substantially reinforced. As such, it weighs about 30 pounds more than an SHP block. The Little M comes with a standard deck height, either 350 or 400 mains, and steel four-bolt main caps on all five saddles. Furthermore, it’s compatible with dry-sump oiling with front and rear crossovers, and has provision for restrictors. The Little M can also be upgraded to 50mm roller cam bearings. On the other hand, the Iron Eagle block is a much more specialized race block. It has the cam location raised 0.391-inch higher than stock to allow the use of large base circle cams, and it comes standard with big-block cam bearing journals, which can be upgraded to 55mm roller bearings. The oil pan rails are spread 0.400 inch per side to clear long stroke cranks. Deck heights from 8.200-9.325 inches are available, providing tremendous versatility. Mains are either 350 or 400 size, and the Iron Eagle has steel four-bolt main caps on all five saddles. Dry-sump oiling and restrictor provisions with front and rear crossovers are also included. The Iron Eagle does not have an oil filter pad, so it requires a remote filter.
Dart has recently expanded the Little M block line to include three variants: the Little M Sportsman, the Little M, and the Little M Pro. The Sportsman version really kind of falls in between the SHP and the Little M. It is cast from premium high-strength iron alloy, and has four-bolt ductile caps on the center three mains and two-bolt caps on the outer mains. It allows for more upgrade possibilities than the SHP as well. In contrast, the standard Little M has four-bolt billet steel caps on all five mains. It is also machined with provisions for dry-sump oiling with front and rear oil crossovers. Stepping things up to the next level, the Little M Pro is essentially the Little M block with a selected menu of upgrades. It can be outfitted in several different ways with options such as larger cam bores and lifter bores, and block lightening options.
From the factory, the small-block Chevy measures 4.400 inches from bore center to bore center, while the big-block Chevy measures 4.840 inches. Dart now offers 4.500-inch bore space small-block Chevy blocks, and 4.900-inch bore space big-block Chevy blocks, including a billet only 5.00-, 5.200-, and 5.300-inch bore spacing. The main advantage of spreading out the bore spacing is that it allows you to use a bigger cylinder bore and still have adequate sealing area between the bores. It is always better to have a large-bore, short-stroke engine combination because it un-shrouds the valves, makes room for larger valves, and reduces piston speed. Most of the 4.500-inch bore space small-blocks are using a 4.250-inch big-bore piston configuration. This enables displacement well in excess of 454 ci while retaining thick cylinder walls for durability and head sealing. The 4.900-inch bore space big-block traces its roots to Pro Stock, and currently most of the spread bore big-blocks have 5.000- or 5.200-inch bore centers. Quite a few custom components are required for these engines in addition to the block itself. They require cylinder heads, intake manifolds, crankshafts, camshafts, pistons, headers, and gaskets are all specific to the spread bore architecture.