Trickle-Down Effect
Dart has been involved in high-end racing since day one, and the trickle-down effect allows the company to incorporate the latest racing technology into its product line. "Innovations such as wet flow-bench testing, Spintron valvetrain testing, and real-world dyno and track testing set Dart apart from the competition," says Jack. "Pro Stock is the most technically demanding class in drag racing, so our Pro Stock engine program-coupled with daily interaction with the country's leading professional engine builders-allows Dart to stay abreast of the latest developments. For example, the Pro 1 and Platinum Series cylinder heads are direct results of Dart delivering Pro Stock technology to sportsman racers."
Stock vs. Aftermarket Blocks
It shouldn't be surprising that a company that manufactures aftermarket blocks recommends using them for most engine buildups. However, that suggestion is a simple case of economics. Anyone who's been nickel-and-dimed to death by a machine shop knows the cost of machining a factory block can be almost as much as the price of a new aftermarket block. Unfortunately, at the end of the day you're stuck with an expensive and inferior factory casting. While you may pay more up front, aftermarket blocks require minimal prep work. "Dart blocks are completely machined and line-honed, and require only a finish hone to the cylinders and lifter bores," says Jack. "The only reason we don't finish them in-house is because every piston and lifter manufacturer has its own tolerances, so there is no one right dimension to finish to. With an aftermarket block, you're putting your money toward hardware instead of labor."
15- and 18-Degree Heads
"The stock valve angle in small-block Chevy cylinder heads is 23 degrees, but Dart also offers SBC Race Series heads with 18-, 16-, and 15-degree valve angles. The head is essentially "rolled over" toward the exhaust side to change its valve angle, which improves performance by creating a smaller, more efficient combustion chamber. Heads with nonstandard valve angles generally have raised intake and exhaust ports that improve airflow, but change the geometry of certain engine components. In order to accommodate these changes, an intake manifold with corresponding raised runners is required. The pistons must be machined to match the new combustion-chamber volume and valve angles. Rolled-over heads use longer valves than stock heads and require compatible rocker arms and longer pushrods to produce optimum valvetrain geometry. If the exhaust ports are raised, new headers are also required."