R&D
"The first step in the R&D process is establishing the goals for the particular block or head we're designing. This sometimes involves working with engine builders and racers who are heavily involved with the engine platform. We look at what needs to stick to stock architecture for usability and what needs to change for performance reasons. CAD 3-D software is used in designing the components, which helps to more precisely evaluate the thickness and types of materials that will be required. It also assists in manufacturing. In the case of cylinder heads, the ports and chambers are developed with wet-flow research to maximize performance. A small run of preproduction parts is made to establish the tooling, molds, and machining programs. The first parts are sent to selected engine builders and racers, who provide valuable feedback. Heads are also sent to piston and valvetrain manufacturers so that they can make parts compatible with the heads."
Alloys
Unless you're an engineer, the various grades of alloys used in automotive applications are difficult to quantify in terms of strength and durability. Instead of the more common A356-T6, Dart prefers using C355-T6 aluminum, which the company says is stronger than any other alloy used to manufacture blocks and heads. "The chief benefit of C355-T6 aluminum alloy in a high-performance engine is that it maintains its strength better at higher temperatures than 356-type alloys," explains Jack. "A356-T6 aluminum begins to degrade in strength at approximately 200 degrees F, while C355-T6 aluminum is not affected until it reaches 300 degrees. This differential can be critical in a highly stressed racing engine. Moreover, C355-T6 offers excellent tensile elongation, resistance to cracking, pressure tightness, and ease of repair."
Virtual vs. Real-World Testing
Computers have helped reduce the amount of trial and error involved in the R&D process and have made measuring techniques far more accurate. But while they are great for things like optimizing strength-to-weight ratios and identifying interferences before a part is made, the ultimate R&D tools remain the dyno and the racetrack. "Trying to make a computer predict cylinder head performance is like trying to make one predict the weather," says Jack. "You can get a reasonable idea of what might happen, but it's not the real thing."