Chrysler first introduced the Magnum engine in 1992 as a 5.2L V8, followed by the 5.9L V8 in 1993. From their introduction until the present, these engines have shared a cast-iron head design that is one of the best production small-block heads offered today. This design was related to the original Mopar small-block commonly called the "A" engine. The block bolt pattern is the same but there are many changes that make the Magnum version somewhat unique. The most obvious way to identify a Magnum head is that the valve cover pattern has 10 attaching bolts rather than the "A" engine's 5. A few years ago, there was only the production cast-iron head, but today there are several Magnum heads and most are newer designs (within the last few months), so they are not well known.
Currently, there are three levels of Magnum heads-production, aluminum, and R/T cast iron. To understand the design of the head upgrades, one must first study the production head. This is hard for an aftermarket manufacturer to do because they only have a final cast piece to look at. Because the Magnum head was designed on CATIA, a 3D computer modeling system used extensively by DaimlerChrysler, Mopar Performance has access to all the OEM technology. The production engineers can run the head through FEA-finite element analysis-to look for high stress areas. Also, a computer flow modeling program called CFD allows you to flow the head on the computer (which also works just as well for water flow through the water jacket). The key to all of these computer formulations is the initial CATIA model, and we have access to all of this information. In fact, we used the FEA stress analysis software to solve a problem on the W2 head which gives it its unique shape today.
As built, the production engineers took advantage of these computer programs and designed a very high flow, small-block head for the Magnum. Mopar Performance wanted to offer our customers an improved head over the Magnum baseline and because this baseline was so good, this goal was not going to be easy to achieve. The old 340 head was a good head in 1968. Whether the 915 casting or the X or J heads, these old A-engine heads can be lumped together but they remained pretty much the same for 20 years. During that era, the best small-block cast-iron head was the W2. When the new 360 replacement head (P4529269 or 340 version-P5249574) was introduced in the late 1980s, it had a lot of heritage to the W2. When the Magnum was designed a couple of years later, this new 360 head was the new baseline.
To design a new cylinder head, we have to do a lot of research before we begin putting lines into the computer. We look at racing rules to see what might be legal or illegal. We talk to our dealers, engine builders, and actual customers to find out what they want. For example, a question to GM racers in one such survey was "why don't you race a Mopar-it makes more power?" Their answer: "your heads are too expensive." Solution: the Magnum head. We introduced the new cast-iron Magnum "race" head P5007374 so that it priced below the new GM head. It uses 31/48-inch stem guides and valves (stainless) P5007375 1.92-inch intake, and P5007376, 1.625-inch exhaust.
Actually, designing a race head is much easier than doing a "street" head or a production replacement head. You don't need big volume, large area, or a big valve port because it loses all of its velocity and doesn't work in this application. The CATIA model helps develop the areas we are modifying. In an aluminum head, weight is a major concern and again the CATIA program helped get the aluminum Magnum weight to 25 pounds, half of the A-engine's cast-iron weight. The CATIA model helps the foundry with tooling by making it directly from the computer model, making the final product both quicker and more accurate.
In the design stage, we are concerned with little things like accessory mountings and bigger things like the amount of water and how it flows and therefore cools. Once the design is completed in the computer, the foundry makes the tooling for the casting and the machine shop writes the machining program. The success of all these steps in the process is directly related to the original CATIA model. Once the finished sample is completed, we thoroughly check it out-measure it, flow it, and then dyno test it on a Magnum engine.
The production Magnum head weighs 49 pounds and flows 190 cfm, which is very good for a production head. The old 340 (-915) family of castings normally flowed between 170 and 180 when they were new. The special race version P5007374 is a better option.
The aforementioned aluminum Magnum head P4876624 was designed to weigh less (at only 25 pounds) and flow more (at 222 cfm, for an improvement of 32 cfm). The combustion chamber is designed somewhat smaller than the cast-iron production head so a direct swap will increase the engine's compression ratio to balance the loss of power caused by the aluminum construction (which conducts heat away from the chamber faster than a cast-iron head). Also, the aluminum Magnum head has inserts in the intake attaching screw holes to allow the same screws to be used as the production heads (without the inserts, the tightened screws would pull out of the raw aluminum). On the valve gear side, one feature we added to the aluminum Magnum were pivots P4876514 and screws P4876963, the same 31/48-inch parts originally developed for high rpm and endurance on the Viper aluminum heads.
The cast-iron R/T heads-P5007140 (or big valve P5007141)-were the biggest challenge to create, because they had to be 100 percent interchangeable with the production cast-iron head and yet offer greater performance. This meant the 10-bolt valve cover, the vertical intake manifold attaching screws, and a 60cc chamber, same as production. Once done, the final version of the R/T flowed almost 230 cfm and makes 20 hp with stock-type engine hardware-hydraulic cam and so on. It's the best cast-iron Magnum head, period.
Finally, remember that the cast-iron Magnum heads are designed with 1.6 ratio rockers and that the engine tends to make more power with more valve lift. So if you install 1.7 rockers P5007404 for the Magnum, you increase the valve lift with the same cam. When playing this high-ratio trick, be sure to calculate your new valve lift and compare to the spring's capacity and piston-to-valve clearances. Generally you should use valve spring P5249464 and retainers P4452032 but some high-lift systems may require an upgrade to P4876062.