Mopar Performance sells the Magnum R/T cylinder heads as bare castings in two variations: one machined to accept the production 1.92/1.625-inch valves (PN P5007140), and another cut for a larger 2.02-inch intake valve (PN P5007141). The head can also be purchased as a complete assembly fitted with the smaller valve configuration (PN P5007145), making the upgrade a bolt-on deal. We recently gained possession of a set of 1.94-inch valve-size castings and decided to run a series of tests to explore their potential. A preliminary examination showed generous and well laid-out intake ports with nicely shaped direct runners leading into a deep bowl, and a tall short-side turn to the valve. Unlike earlier production heads, the valve-guide boss protruded only minimally into the air stream. To accept the production valvetrain, a hump at the inlet side of the runner was required to clear the pushrods. the shape is highly defined, and the protrusion is minimal for an as-cast port. In short, the intake runner was a nice design, hitting all the marks in requirements for an excellent high-performance head casting. The exhaust ports also showed excellence in design, again with a deep bowl, straight runners, a nearly ideal short turn, and minimal guide boss intrusion. The exhaust layout is strikingly similar to the race W-2 port configuration, but retains an exit and flange pattern that accepts stock exhaust manifolds or conventional headers.

Flow Fascination
We brought the cylinder heads, along with our porting kit, to Westech Performance Group to steal some time on their FlowCom-equipped, SuperFlow 600 flowbench. The goal was to run some tests to quantify the flow numbers in as-delivered condition, and run through some basic modification to gauge how these casting respond to porting modifications. The heads were first base lined as cast, with the production valve machining and stock production 1.92/1.625-inch valves. The results are shown in tables 1 and 2, column one. The intake port flow was right in line with our expectations, reaching the mid-220's with peak flow coming in at .550-inch, and then leveling off. These are good numbers for an as-cast iron head, particularly with the stock 1.92-inch valve-enough to comfortably support the 450-plus-horsepower range. The intake port flow was significantly better than any production iron small-block head. The exhaust flow was outstanding, reaching numbers out-of-the box that are rarely seen with fully race-ported early heads, and light-years ahead of any of the as-cast iron stock heads. It was interesting to note the exhaust port was nearly dead quiet on the flowbench at higher lifts-indicating very little turbulence.

With the preliminaries out of the way, it was time to do a little carving to further explore the head's potential. We would structure the mods in a sequence that would follow a progression of modification levels. We would record the flow improvements along the way, allowing anyone interested in duplicating our efforts the option of choosing how far they want to go. All of our mods would retain the production valve seat machining and stock valves. Since the stock valves and seat machining would be retained throughout our testing, port flow below .300-inch lift-which is primarily dictated by the valve and seat form-would be changed very little.

The first step is to perform a simple bowl blend where the valve job machining is blended into the as-cast bowl. With just a bowl blend, both the intake and exhaust ports picked up substantially (tables 1 and 2, column two). Intake port flow was up nearly 20 cfm at .500-inch lift, while the already outstanding exhaust also made significant gains. Blending the bowls is a simple mod requiring very little special know-how or skill, but improves the flow solidly. Bowl blending the heads can be quickly accomplished even by a beginner, and based on the return for the amount of work involved, we can see no excuse not to perform this level of modification.