Mopar's Magnum series of engines were Chrysler's play at stepping up the venerable small-block to keep pace with changing engine technology requirements. This kept the series alive and succeeded in making Mopar engines more than competitive. Among the improvements were extensively redesigned cylinder heads. Magnum heads addressed more demanding requirements in terms of both power production and emissions by increasing efficiency. Compared to older head designs, the Magnums stepped up efficiency on a number of fronts. First, airflow was improved with higher-flowing ports, which picked the intake flow up significantly. Dramatic improvement of the exhaust port layout was also accomplished. Mechanically, the valvetrain was upgraded with the use of higher ratio rockers, stepping up the leverage from the traditional 1.5:1 ratio to 1.6:1. Perhaps the most significant step forward was in the combustion chamber. While the earlier cylinder heads carried a fully-relieved open-chamber layout, the Magnum design utilized a double quench closed-chamber configuration-a superior arrangement in both power production and efficiency. The icing on the cake was changes to the manifold and valvecover attachment, putting an end to the decades-old problem of oil seepage and frustrating leaks.

Standard Magnum heads offered great power at the levels demanded in OEM applications at the time. however, the head was conceived with truck production in mind, not all-out, gut-wrenching power. Be that as it may, with enough cam and compression, stock-production Magnum heads could achieve outputs of just over 400 gross STP horsepower at the crank. To allow output to move to the next level, Chrysler's Mopar Performance introduced the Magnum R/T cylinder heads. These cylinder heads feature all the benefits of the Magnum design, but step up the power potential with larger, better flowing ports. The Magnum R/T increases intake runner volume from the production Magnum size of 153 cc to 180 cc, and is a direct bolt-on replacement for the production piece. While a stock Magnum will flow in the neighborhood of 190 cfm on the intake side, the R/T-in out-of-the-box form-will pull flow in the range of 220-230 cfm-an improvement of better than 10 percent.

Now, we've already stated the production Magnum head can support 400 hp, and maybe that power potential seems like plenty for the average street mill. but the Magnum R/T's superior ports will make more power with the same basic engine combination, and will require a less radical combination to achieve the targeted output. While building a 400hp engine using the production heads will require a fairly nasty camshaft, getting there with the high-flowing Magnum R/T heads can be done with a more conservative and street-friendly combination. It's all in the airflow. Gaining big increases in output without relying on radical cam timing becomes a significant consideration in late-model MPI applications, where low vacuum and high overlap can cause havoc with the computerized engine-management systems.