I’m sure the question has crossed your mind: Why not a 3rd Gen 5.7, 6.1, or 6.4 Hemi instead of the Magnum engine? The Hemi is newer, uses an aluminum block and heads where the Magnum uses iron, and the Hemis have a higher power rating than the 5.9 Magnum ever had. Besides, if you use a Hemi, you get to slap one of those cool “Yeah, it’s got a Hemi” bumper stickers on your car.
While there are definite advantages to using a new Hemi over a Magnum, the advantages for the Magnum are pretty significant.
Cost
The expense of the new Hemi swap is daunting indeed. First off, the crate and junkyard Hemis cost substantially more than the sub $1,000 junkyard Magnum engine, putting you significantly behind, expense-wise, from the beginning. Unless you get a free/very cheap Hemi, your total cost for a fire-breathing junkyard Magnum will probably be less than the cost of the Hemi engine alone.
Then there’s the expense of the swap itself. To install a new Hemi into a classic Mopar, a Hemi requires a different radiator, expensive custom headers and mounts, an aftermarket brain box to fire the coil packs and run the drive by wire throttle assemble, an expensive fuel injection system, or an equally expensive manifold and distributor for carbureted use. The Magnum uses common LA exhaust parts, engine mounts, and radiator. There are other requirements for Hemi swaps, but you get the idea.
If the additional cost of swap parts and the engine itself doesn’t dissuade you, there’s also the cost of performance upgrades. If you’re unhappy with the power your Hemi makes as-is, it’s going to cost a significant amount of money to upgrade it. One well-known Hemi vendor sells camshafts for the new Hemis for $800, and a carbureted intake manifold for $800.
I’m certain that as this is being written, the cost of this swap is coming down. Given time, there will be even more Hemi engines available, and the cost of the swaps will further decrease.
However, the last sticking point is still pretty hard to overcome, and that’s something that every Mopar guy can understand. Power! The fact is, Hemi engines just aren’t making more horsepower than the hot-rod Magnum engines. Sure, you throw stock Magnum up against a stock 6.1 Hemi, and the Magnum will come out on the losing side every time. But leaving things stock isn’t part of the typical engine swap plan…
In short, the Hemi will cost substantially more, require considerably more work and re-engineering of your car, and deliver roughly the same (or worse) performance as a Magnum engine.
Car Craft details a lot of the steps necessary for a new Hemi swap.
Car Craft Hemi Swap details
Hot Rod Magazine did us a favor and wrote an article detailing the swap (but not the cost):