How to Build Killer Chevy Small-Block Engines. Mike Mavrigian
many hours and multiple machining operations, CNC block machining can be accomplished in a matter of minutes, with an incredible level of precision.
Despite the OEM development of current-day sophisticated engine platforms, such as the LS and LT series, the Gen I small-block Chevy engine continues to enjoy widespread acclaim and popularity for both street performance and racing applications. You simply can’t go wrong with the beloved small-block platform. It’s a true American icon.
The array of superior engine components available for the SBC is truly mind-boggling. All of today’s high-level aftermarket components evolved from the initial OEM designs to offer incredible advancements in performance and durability.
CHAPTER 2
THE BLOCK: WHERE IT ALL BEGINS
From the inception of the Gen I small-block Chevy engine to the current LS and Gen V LT variants, they all share a few common basic traits: a 90-degree V-8 platform, 4.4-inch cylinder bore spacing, a single overhead valve camshaft, and a pushrod connection between the lifters and rocker arms.
As most enthusiasts already know, the small-block Chevy engine has been around since 1955. Over the years, displacement, strength, durability, and machinability (in terms of allowing modifications) variations have proliferated. Modern aftermarket blocks are available to accommodate much larger displacements and design variations than in days past in terms of both bore diameter and stroke increase increments as well as the ability to withstand higher cylinder pressures and operating speeds.
The Generation I small-block Chevy engine just keeps getting better with age. By age, I refer to non-stop development to enhance its capabilities. Refinements over the years have resulted in today’s extraordinarily robust and versatile performance platform. Perhaps no other engine platform in the history of the internal combustion engine has experienced more evolutionary enhancement changes than the venerable small-block Chevy engine. A prime example of those improvements to foundation componentry is the engine block. Currently available blocks specifically suitable for high performance include cast iron (of varying nickel content), cast aluminum, and billet aluminum.
Cast Iron Versus Aluminum
For both street and many racing applications, cast-iron blocks are perfectly acceptable. The inherent advantage of alloy blocks is obvious in terms of weight reduction: cast-iron blocks typically weigh in the area of 170 to 240 pounds, while aluminum blocks can weigh as little as 80 pounds, depending on various lightening options offered by some makers. Weight reduction is also necessary for certain forms of racing (sprint car racing, for example). Another advantage of aluminum is the relative ease/ability to be welded to repair certain failures, such as cracks, broken mounting tabs, etc.
Cast-iron blocks can be overbored within the limits of specific designs, while aluminum blocks feature iron cylinder liners that limit bore oversizing. Today’s aftermarket iron blocks typically feature thicker decks for increased rigidity, thicker cylinder walls that permit more overboring than OEM blocks, and improved cooling and oiling passages. Aluminum aftermarket blocks are available for designated bore sizes to suit just about any desired application. One major difference, aside from the weight difference, is cost. Aluminum blocks are more expensive than cast iron. New cast-iron aftermarket blocks generally run in the $2,000 to $3,000 range, while new aluminum racing bare blocks can cost as much as $5,000 to $6,000.
While today’s cast-iron aftermarket performance blocks are superior in strength and rigidity, some companies also offer compacted graphite iron (CGI) blocks, which offer increased material density and strength. (Photo Courtesy Dart)
Unless your racing application demands the use of an aluminum block, stick with cast iron. We won’t waste time by delving into vintage OEM mass production cast-iron blocks. For purposes of this book, we’ll only discuss currently available blocks offered by qualified aftermarket manufacturers.
A cast-iron block’s material makeup can differ depending on the iron mix from gray iron or nodular iron to iron mixed with a level of nickel for increased hardness to CGI (compacted graphite iron). CGI features a molecular makeup that creates tightly interconnected graphite during the casting process that offers increased hardness, increased fatigue strength, superior ductility, and greater tensile strength. CGI is less brittle and more stable than gray iron. Several aftermarket block makers now offer CGI blocks. Due to the increased strength, a block can be machined for further weight reduction without sacrificing strength compared to a gray iron casting.
For instance, cylinder bore walls can be machined thinner without sacrificing wall integrity and strength. CGI is 75 percent stronger than gray iron and approximately 200 percent more resistant to fatigue. This makes CGI a good choice for racing blocks that need to withstand extreme pressures and temperatures. Also, due to the increased strength level, a CGI block can be machined to reduce weight by as much as 22 percent compared to gray iron.
Main Caps
On the subject of main caps, we generally have three choices: ductile iron, nodular iron, and steel billet. While steel billet may initially seem the strongest, there are factors to consider. Some view nodular iron as the best choice for cast-iron or aluminum blocks that will experience substantial dynamic pressures, since nodular iron caps tend to be more ductile and will move before they break. With that said, nodular iron or steel billet caps are considered by most to be the best choice in terms of strength and rigidity, and they are the least affected by thermal and dynamic stress, depending on builder experience and preference. ■
For any high-performance application, a block should feature four-bolt main caps, which offer much greater rigidity to cope with the pressures of high-revving crankshafts. This reduces crank deflection and harmonics and offers superior clamping force for the main caps compared to early non-performance two-bolt main cap designs. All aftermarket performance blocks feature four-bolt main caps, many featuring splayed outer bolts at the number 2, 3, and 4 cap locations. The splayed outer bolts (usually at about a 10-degree angle) enter toward the side of the block where there’s more material thickness as opposed to the bottom of the main web, which increases cap rigidity.
Aftermarket engine blocks feature superior casting materials and techniques. They are cast and raw machined to much tighter tolerances than vintage mass-produced Chevy OEM blocks. A Dart cast iron Little M block is shown here.
OEM Blocks
The use of OEM or stock blocks has served well as the foundation for street performance and racing applications. That was then, and this is now. Today’s performance aftermarket now offers a dizzying array of block upgrade designs.
All performance aftermarket blocks feature four-bolt main caps. Depending on the specific block, the outer bolts may be straight on all caps, or caps number 2, 3, and 4 will be splayed at an angle.
Aftermarket performance blocks feature four-bolt main caps with the outer bolts or studs on caps number 2, 3, and 4 splayed at an angle, providing stronger fastener clamping force at a thicker area of the outer block instead of the bolts engaging into the bottom of the main webs. The example seen here is a Dart Little M block.
Aftermarket blocks (such as the Dart Little M shown here) typically feature relief cutouts at the pan rail sides to accommodate increased stroke. The block maker anticipates that the builder plans to use a longer crankshaft