Despite having been on the market for decades Dart’s Pro1 big-block cylinder heads receive constant upgrades. In fact, this is the essence of their universal appeal—their development never ends.
Originally introduced in 1982, David Reher of Reher Morrison says, “There is nothing that compares with the Pro1. They have been the best bang for the buck for years and even more so now.”
Devised to bring Pro Stock technology economically to Sportsman racing the Pro1 is particularly popular in drag racing categories: Super Gas, Super Comp, and Bracket classes as well as in boat competition. Using 24-degree intake valve angles while retaining the original 4-degree cant angles, the Pro1 is also ideal for high-performance street cars. Importantly, it offers five different intake runner volumes. The 310, 325 and 345cc versions are provided in as-cast condition while 335 and 355cc designs are produced as fully CNC-ported.
The advantage of having five different runner volumes available has evolved to satisfy a wide variety of engine displacements, rpm ranges, gearing and other governing factors. Crucially, they provide the ability to deliver peak power at 7,500rpm or cruise at 2,700rpm.The two chief benefits of the as-cast runners and combustion chambers are simple: they perform as well as their fully CNC-prepared counterparts and they are inexpensive.
Moreover they operate with standard intake manifolds and valve train components, including original equipment studs and rocker arms and guides. Raising the exhaust port locations by around 0.300 inches is perhaps the upgrade that yields the Pro1’s greatest single power gain. In so doing, the port’s short-turn radius was increased, ending a perennial problem with the original big-block head design.
To cultivate better flame travel and to improve clearance of custom piston domes the spark plugs were relocated. Using data from Dart’s wet-flow bench, repositioning was carefully executed to avoid provoking plug wash during the valve overlap cycle: when the intake is opening and the exhaust is closing.
Other major innovations that distinguish the Pro1 lie within its castings. Created from the latest precision, lightweight formula, its weight is distributed evenly with consistent wall thicknesses and water jackets. As a result its cooling rates are uniform. Though festooned with fine engineering, the Pro1’s most visually pleasing element is probably the blending of the valve bowls to the ports—one of its many triumphs. As Dart’s Dick Maskin says “When you look at a Pro1 you soon realize no further work is necessary.”