Porting 383/440 Aluminum Replacement Heads - Power Porting

Mopar Performance has been in the aluminum head market for quite a few years now with their Stage VI variations, which deliver the one-two punch of more power and lighter weight. The Stage VI heads feature raised runners, which result in a widened span between the pair of heads when bolted on an engine. Naturally, this requires a wider-than-stock intake manifold. The clever feature of these heads is that the intake runners are raised exactly enough to line up an RB intake on a B engine, although RB engines still require a dedicated wider Stage VI intake or spacers.

Hidden in the MP catalog is a new aluminum 383/440-replacement head. The 383/440 heads feature many of the design improvements of the Stage VI heads, such as the modern quench-style combustion chamber and revised runners, but have the stock intake port location. This configuration makes the new 383/440 aluminum head more of a bolt-on replacement, and opens the door to a wide range of conventional intake manifold choices for RB engines without the need for manifold spacers. We ordered a set and evaluated the airflow potential.

Baseline And Design Characteristics
MP's #P4876311 aluminum replacement big-block heads are sold as bare castings, and come cut for the familiar 2.14- and 1.81-inch intake and exhaust valves, respectively. They accept all the stock-specification valvetrains, either the factory stuff or any of the high performance aftermarket components designed for the OE-style heads. An exhaust crossover provision is provided. Being aluminum, there is a weight savings of approximately 50 pounds for the pair compared to production iron heads-a significant reduction of front-end weight in a big-block car.

The heads are fitted with heavy-wall bronze valve guides and hardened steel valve seat inserts. Most significantly, they carry relatively compact 78cc closed combustion chambers. The chamber design is some 12cc smaller than the open-chamber iron production design, boosting compression ratio. Since aluminum heads will typically tolerate an additional point of compression ratio as compared to their cast iron counterparts, the smaller chambers offer a complementary change. Beyond the added ratio, the closed chamber allows for increased combustion efficiency by facilitating the incorporation of quench and squish effects when building the engine. A flat top piston at zero deck, along with a common .040-inch gasket, will yield the desired result. The rewards include greater detonation tolerance and a significant increase in torque production over an open chamber head. Significant for some is the stock-appearing end profile which, unlike most aftermarket aluminum heads with flat milled ends, looks like an iron head if painted.

Mopar Performance claims the 383/440 aluminum head, out of the box, will outflow the factory #906 heads originally fitted on '68-'70 big-blocks (and are generally regarded as the best standard production heads). This they did handily (refer to the numbers in tables 1 and 2, columns 1) in our independent testing. This compares to peak flow numbers in the 210-225 cfm range for stock #906 intake ports. As replacement heads, they greatly outpaced the stockers, but this was only scratching the surface of the heads' ultimate potential with additional porting.