It may look nearly indistinguishable...
It may look nearly indistinguishable from stock at first glance, but Dart's new Iron Eagle cylinder head for 351 Ford Windsors is capable of big performance gains over the original heads from Ford.
The key to success in stock-based racing classes often is to find the right combination of parts allowed by the rulebook that will make the best power. Usually, there are few modifications permitted and no race parts allowed. But racers are allowed to substitute parts as long as they are "stock replacement" components.
And that is where the smart racer can get an edge. "Stock replacement" is supposed to mean no real performance or reliability difference versus the original parts. But a lot has changed since Ford first designed its cylinder heads for the 351 Windsor over two decades ago, and a smart manufacturer can produce a cast iron set of heads that look just like the original Ford units on the outside but perform much better.
That's exactly what Dart did when it added a Ford Windsor head to its Iron Eagle lineup. For Street Stock and other stock-class racers, Dart's Iron Eagle cylinder heads for Ford utilize what the company calls its Speed Flow technology, which includes wet-flow testing and computer-aided design and manufacturing. Although the head is as-cast with no CNC cutting of the ports or combustion chambers, the valve guide bosses are designed to be as streamlined as possible and the ports are updated over Ford's original designs to maximize performance. Also, the intakes feature five-angle seats while the exhausts are radiused while the valves themselves are back-cut to enhance efficiency.
Still, this head should qualify as a stock replacement (if you keep quiet about the five-angle intake seat part), because it is still your basic cast-iron, unported design complete with the stock Ford port locations, bolt patterns and valve angles. It is available with either 58 or 62cc combustion chambers. The 185cc intake ports are said to flow 245 cfm at 0.500 valve lift while the exhaust ports, sized at 73cc, are capable of 159 cfm at 0.500 valve lift.