Hot rodders played with blocks as kids, and still play with them as adults. This vast level of experience notwithstanding, enthusiasts often insist on monkeying around with production blocks. They might be cheap, but after you've paid a painful $1,000 to $2,000 machine shop bill, it's still a production block that was never designed to handle the rigors of a street/strip or race application. While a stock block might work fine for a mild rebuild, with the power potential bequeathed by modern cylinder head and valvetrain technology, not many people are content with mild rebuilds these days. A cool 600 hp is becoming the new benchmark for small-block performance, and unless that Rat motor build hits 800 hp, a big-inch Mouse could very well put the hurt on you at the track. For serious stroker engine combos, the option of investing in a high-quality aftermarket block makes too much sense to ignore. Not only are they far stronger than the typical stock casting, they offer thicker cylinder walls and taller deck heights for increased displacement potential, improved oiling and cooling systems, and costly machining operations have already been performed prior to shipping. To get a handle on what to expect when stepping up to an aftermarket block, and how to choose the right options for your application, we consulted with Jack McInnis of Dart, Jason Neugent of Brodix, and Rocko Parker and Jeff Kettman from GM Performance Parts. Here's what we learned.

Aftermarket Block Basics
Jack McInnis: "Many people use production blocks to build performance engines, but aftermarket blocks offer several advantages in terms of durability and value. Aftermarket blocks are designed and manufactured for a completely different purpose than production blocks. Stockers were made with cheap production cost as top priority and were never intended to hold the kind of power we're making today. When the production small-block Chevy block was first designed, no one could have dreamed of the power potential today's cylinder heads and valvetrain components would provide. Aftermarket blocks benefit from decades of technology, both in racing and manufacturing, that has transpired since the original designs were made. Metallurgy, machining techniques, and overall design features are all vastly improved. The castings are designed with thicker cylinder walls which allow larger bore sizes and superior ring seal. Dart blocks also have thicker decks, and various deck heights are available to allow more flexibility in designing engine combinations. Likewise, the main caps are much stronger, and the water jackets are enlarged to enhance cooling. Another consideration is that decent used cores are getting harder to find, and by the time you have one cleaned, machined, and checked, you've spent very close to what a new aftermarket block would have cost. With an aftermarket block, you're putting your money towards hardware instead of labor."

Jason Neugent: "An aftermarket block is usually made at a slower pace and is a product of greater attention to detail than a production unit. Unlike a production block, strength and accuracy are the primary goals. Block tolerances must be tight, and stability in the cylinder sleeves and mains is critical as well. All these issues are addressed with an aftermarket casting. Additionally, aftermarket blocks have several options available, such as a variety of bore sizes, cam heights, deck heights, and lifter bore diameters. That just gives an engine builder much more flexibility in terms of displacement options, bore and stroke configurations, and valvetrain selection. Our blocks also feature reinforced lifter valleys, splayed billet mains, increased pan rail clearance, and revised oil passages. By far, the most compelling reasons to go with an aftermarket block instead of an OEM unit are because of their much tighter tolerances and stronger casting design."