Chevy Vortec Cylinder Heads - King Vortec

Now for the aftermarket. Dart Machinery is a high-tech company that uses its knowledge in NHRA Pro Stock racing to develop cylinder heads, blocks, and intake manifolds for the high-performance enthusiast. Initially, we were told that Dart wasn't interested in competing in a power test because this particular head was not designed as a power piece. Instead, it was conceived as an inexpensive OE replacement for major engine rebuilding facilities across the country, and that given the end user, Dart racing technology was not incorporated in this casting. After numerous phone calls and a promise that we would be clear about the head's intention, Dart decided to join in the fun. We figured it would be interesting to see how well this OE replacement head would fair against performance pieces that were designed to make power.

During the assembly session there was a sense of uneasiness in the dyno cell as each of us had our opinion as to how the Dart head would do. One felt that the 165cc intake runner would limit intake flow while another thought that the 3cc (0.3:1 compression difference) larger combustion chamber would hurt torque across- the-board. The Dart and Vortec both have center-bolt and perimeter-bolt valve-cover patterns, screw-in rocker stud bosses (studs not included), and feature the nicest raw casting of the bunch. Soon enough, the engine was ready and we pulled the handle.

Low-speed torque was down a hair, 361 lb-ft at 2,000 rpm, but peak torque was 424 lb-ft at 4,000 rpm. Peak horsepower was 384 at 5,400 rpm, showing a definite restriction in intake runner size. What's interesting is that the little 165cc intake runner was able to consume a whopping 633 cfm at its highest point of volumetric efficiency. This told us that the small runners were restricting air through the cylinder head because the actual ports themselves were moving all the air they were given. Without a doubt, these heads would see a major improvement with a little polishing around the valves and porting the intake runners to match the intake gaskets. The average numbers were 393 lb-ft of torque and 289 hp across-the-board. Considering these heads weren't designed for performance, they did quite well.