How to Build Killer Chevy Small-Block Engines. Mike Mavrigian
thickness on OEM blocks can vary greatly, sometimes to the point of not providing the rigidity required for high compression and negatively affecting cylinder bore roundness (cylinder bore distortion). Aftermarket blocks tend to feature much thicker decks, as thick as 0.675-inches, that provide superior strength, reduced cylinder bore distortion, and superior head gasket sealing when the cylinder heads are clamped in place. Cylinder wall thickness is also improved in aftermarket blocks in terms of both minimum thickness and improved consistency of wall thickness around the entire perimeter of the cylinder wall. This increased thickness further limits cylinder bore distortion and allows the builder to increase bore diameter further without weakening the cylinder walls.
OEM blocks may feature wall thicknesses as thin as 0.194 inch in the thinnest spots, while aftermarket blocks may provide minimum thickness in the 0.220- to 0.308-inch range even when cylinders are finished to a 4.125-inch diameter. Many aftermarket blocks feature siamesed bores with no water jackets between cylinders. This provides superior rigidity to the cylinder walls with less dynamic deflection, which also helps to minimize cylinder bore distortion. Controlling cylinder wall geometry (in an effort to maintain as much uniform roundness as possible during engine operation) reduces frictional drag and improves piston ring sealing.
While the standard small-block cam bearing bores are 2.000 inches, aftermarket blocks are available in a variety of bore sizes depending on the cam journal and/or the type and size of the cam bearings. A popular move is to use a small-block cam that features big-block cam journals of 1.949 inches in diameter, requiring cam bearing bores of 2.120 inches. This allows the use of an increased-mass cam core for added cam rigidity for less deflection when using with high-pressure springs. Even larger cam bore sizes of 2.250 inches are available for the use of needle roller cam bearings. Choices of cam bearing bores include 50, 55, and 60 mm. The cam bearing bore size can be specified when ordering the block. The aftermarket offers a high level of versatility compared to working within the constraints of an aged factory production block.
Today’s quality aftermarket blocks offer vastly superior strength and rigidity with less metallurgical movement under thermal and dynamic stress. With these superior blocks, coupled with the ability of today’s engine builder to accurize critical dimensions with either specialty blueprinting machining fixtures or multi-capability CNC machining, we have the best that today’s technology offers to produce blocks capable of running and sustaining extremely high engine speeds. They can withstand the extreme cylinder pressures obtained through the use of high compression and/or high-boost forced induction. Unless you’re planning a true historic restoration where you feel compelled to salvage a vintage block, today’s aftermarket blocks are the better choice performance-wise, especially considering the quality offerings from such manufacturers as Dart, Chevy Performance, Brodix, and Donovan.
Dart
Dart provides the following offerings.
SHP Pro Iron
This is an excellent upgrade or stock replacement. Designed for street high-performance or sportsman racing and special high performance (SHP), this block is ideal for hot rodders, drag/circle track, off-road, or high-performance marine applications. For a few dollars more than you’d spend on a 40-year-old core that needs cleaning, machining repairs, and upgrades, this provides a new foundation for your build.
Many features provide superior performance and durability, including a priority main oiling system, Siamese cylinder bores with extra-thick walls, thicker decks for superior head clamping and gasket sealing, blind head bolt holes that don’t enter water jackets, scalloped water jacket walls that improve flow around cylinders, and pre-clearance for a 3.75-inch stroke. Other features include splayed outer bolts on the middle main bearing caps, provisions for OEM stock roller lifters and cam, the use of 0.300-inch-tall stock 1987–1995 roller lifters, acceptance of the 1981–1985 stock-style oil pan and dipstick, and all OEM-location bolt holes for the starter, clutch ball, etc.
Race Series Aluminum
This weight-saving cast-aluminum racing block is offered in deck heights from 8.850 to 9.500 inches. The casting features a premium and proprietary high-strength RMR aluminum alloy. Cylinders are extended at the bottom for better piston support when used with long-stroke cranks. A raised cam tunnel provides added clearance for strokers. The cam tunnel is raised by 0.391 inch with an option for a 0.434-inch raise. Siamesed bores are offered in 4.000 inches or 4.125 inches and can be safely bored to as much as 4.165 inches. Ductile-iron cylinder sleeves and extra-thick walls provide an excellent ring seal.
The oil pan rails have been spread out by 0.400 inch at each side for more stroker clearance. This small-block platform features big-block cam bearings, allowing the use of larger base circle cams to reduce twisting with cam-driven pumps. Rear external oil inlets with crossovers and restrictor provisions located in the center of the lifter valley simplify external oil pump plumbing. This block has no provision for a block-mounted oil filter, so a remote filter is required.
Dart’s SHP Pro Iron block is pictured. (Photo Courtesy Dart Machinery)
Race Series 4.500 BS Aluminum
This enhanced version of Dart’s cast-aluminum racing block is similar to the aforementioned race series aluminum block but features a 4.500-inch bore spacing and permits bore diameters up to a whopping 4.250 inches. Head bolt patterns are offered in either a standard 17-bolt or optional 19-bolt version. Deck height choices include 8.850, 9.025, or 9.075 inches. Tall-deck versions are also available at heights of 9.325 inches or 9.500 inches. The range of deck heights allows greater versatility for the preferred rod angle and ratio. Standard is a 0.391-inch raised cam tunnel, which provides a camshaft-to-crankshaft centerline of 4.912 inches. An optional 0.434-inch raised cam is also available.
Little M Sportsman Iron Block
This block is another offering from Dart that is ideal for a serious street performance build, sportsman racing, or a marine application when the builder wishes to use standard-type Chevy small-block parts, such as the cam, timing chain, oil pump, oil pan, oil filter, motor mounts, mechanical fuel pump, clutch linkage, etc. Improvements over a factory block, in addition to Dart’s stronger casting and higher precision machining, include priority main oiling, where the main bearings are fed first, Siamese cylinder bores with extra-thick walls (a minimum of 0.275-inch thick even with a 4.185-inch bore), scalloped water jackets, an open lifter valley for improved oil return, enlarged lifter bosses that accommodate offset and oversize lifters, blind head bolt holes that don’t enter water, splayed outer main cap bolts on middle caps, a rear external oil feed, and crossover and restrictor provisions.
This is an example of Dart’s cast-aluminum small-block bare block. Cast-aluminum blocks are slightly more expensive than cast iron but cost substantially less than billet blocks. If weight savings is important and you can’t afford billet, this is a great choice. (Photo Courtesy Dart Machinery)
Dart’s Little M Sportsman iron block is shown. Like all Dart blocks, options include the desired bore size, deck height, and standard or raised-cam versions. (Photo Courtesy Dart Machinery)
Little M Iron Block
The Little M is a true cast-iron racing block suitable for street or track. Like the Little M Sportsman block, it accepts standard SBC parts with all of the features of the Sportsman version. The Little M is fitted with billet steel four-bolt main bearing caps and is available in a CGI (compacted graphite iron) version that doubles strength without adding weight, making it a good choice for boost applications (turbo, supercharger, or nitrous). The Little M is beefed up in critical areas and designed from the ground up as a true racing block that can be used with off-the-shelf SBC components.
Little M 305 Water Iron