CNC Porting
Those who swear by hand-ported heads balk at the ridges left behind by CNC porting. However, a port finish that's too rough is better than one that's too smooth, and most high-end race teams opt for CNC porting. "The main advantages of a CNC-ported head are consistency and price," says Jack. "The CNC machining centers can duplicate a port shape over and over with absolute precision-and in far less time than hand porting-which helps reduce our retail prices. We generally only use hand porting for R&D purposes and custom blending."
The Little M block is a performance version of the standard small-block Chevy, and can use most stock-type components. The Iron Eagle block is like a Rocket block, with a raised cam location and spread oil-pan rails.
Repair or replace?
Cracked cylinder heads can usually be repaired, but the question is whether r not it's worth the trouble. In many instances, it may be more economical to replace rather than repair the head. "Welding cast iron is difficult and expensive, and since the price of new cast-iron heads is relatively low, most of the time it is more cost-effective to purchase a replacement," explains Jack. "In contrast, the C355-T6 alloy used in Dart aluminum cylinder heads can be welded easily, although this work should be done by an experienced professional to avoid weakening the metal. The success of a repair really depends on the skill of the technician."
Porting Services
Dart heads are manufactured with a precision casting process that produces extremely accurate port shapes. Even in unmodified form, Dart says that its as-cast ports produce great airflow. For the racer who wants more performance, Dart offers several levels of porting. "The first step is our Super Mod porting, which includes CNC machining of the valve bowls, combustion chambers, and port entrances," explains Jack. "The Super Mod Complete option adds a precision valve job, valve guide sizing, and hand blending. The next step is Full Port, which includes complete CNC machining of the intake and exhaust ports and combustion chambers. The ultimate package is Full Port Complete, which adds a precision valve job, valve guide sizing, and hand blending."