We hooked up some of MP's new #P4876311 383/440 aluminum replacement heads. Ultimately des
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.
All flow testing was performed on Westech's SuperFlow 600 flow bench at 28-inches depressi
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.
Rick Stoner at Westech lined us up with this rollover cylinder head stand from TDA. It rot
Step one was a competition valve job on a Serdi seat cutting machine, including sweeping t
The first cut was just a mild bowl blend, removing the sharp edge left by machining where