Tolerances
"Dart's iron and aluminum castings are produced at foundries in the U.S. with whom we have long-standing relationships. We design and machine our own tooling for greater control of the mold-making process. Even with state-of-the-art mold making and foundry technology, castings always will have some variation. We qualify every single block prior to machining to maximize the cylinder-wall thickness in the finished piece. Factory blocks are machined from an external datum to simplify production, so the cylinder walls can be very inconsistent. Similarly, we fine-tune our cylinder-head machining programs constantly to ensure that valve locations and other critical dimensions are always optimal within each new casting lot. Dart's CNC-machining centers are built to hold extremely tight tolerances over long production runs. Our fixtures are designed to reduce the number of setups required and reduce stack-up tolerances. We inspect our cutting tools at specific intervals to ensure that surface finishes are optimal in the machined parts. Finally, we constantly inspect the finished blocks and heads for quality."
Wet Flow Bench
Over time, the wet flow bench may prove to be one of the most significant breakthroughs in cylinder-head development. By introducing an industrial solvent-whose specific gravity is similar to that of gasoline-into the flow bench's airstream, engineers can now see how air and fuel interact in the combustion chamber by illuminating the solvent with a black light. Dart is one of the few aftermarket manufacturers that incorporate this technology into their products. "The wet flow bench has enabled us to dramatically improve the efficiency of our cylinder heads," says Jack. "For example, our Pro 1 cylinder heads were redesigned this year utilizing wet-flow research. The new version, called the Platinum Series, is up 20-25 hp over the old-style Pro 1, but the dry airflow numbers are almost the same. The air/fuel mixture is much heavier and behaves very differently than dry air, so managing the mixture efficiently gives much better results than just increasing airflow. We've been able to increase the amount of fuel the ports will pull, resulting in increased power and torque."
Coatings
Dart is well known for its top-notch blocks and heads, but the company also offers coating services to its customers. What started as technology reserved for the aerospace industry and high-end racing circles is now available to the average enthusiast, and the benefits of coatings are many. "In addition to the familiar antifriction and antigalling coatings often seen on pistons and bearings, Dart offers dry-film lubricants, oil-shedding lubricants, ceramic thermal barriers, and anticorrosion coatings," explains Jack. Dart can coat almost any internal engine component to improve its performance or durability. "We can apply oil-shedding coatings to the crankshaft, connecting rods, and oil pan to reduce windage, as well as coat the combustion chambers in aluminum heads to retain heat. Coating the exhaust ports keeps the exhaust gases hot, which increases their velocity and improves cylinder scavenging. Intake manifolds can be insulated with a coating to increase the density of the air/fuel mixture, which produces more horsepower. Valves in turbocharged engines can also be coated with ceramic to withstand the intense heat."