How to Add 129hp to a 5.9l Mopar Magnum

Chrysler unceremoniously unveiled the 360ci (5.9L) LA-series small-block V-8 in 1971 as a low-compression engine with only a two-barrel carburetor. The 4.00-inch-bore-by-3.58-inch-stroke powerplant was originally designed to provide an economical alternative to the popular 383 two-barrel big-block, while the shorter-stroke and larger-bore (4.04x3.31) 340-cube engine carried the performance banner. With the cancellation of the 340 engine option after the '73 model run, there were a few performance variants of the 360 in the early and mid-'70s, though these were all low-compression engines with the further disadvantage of add-on smog-control equipment. There really was no love for the 360 engine in the early years, which developed an unflattering reputation as a low-performance "smog motor." It took decades for this impression to lose its hold. Eventually the 360 earned acceptance from the Mopar crowd, and its popularity has grown ironically to become one of the favored powerplants for performance use, especially when the objective is high output on a real working man's budget.

The 5.9L Magnum engine was a big step forward in the 360's evolution. By the early '90s, the 360 was seriously dated, especially compared with engine packages offered by competitive manufacturers. Looking to gain an edge on the competition for a minimum of development cost, Chrysler gave the old warhorse a significant facelift, reintroducing the engine as the 5.9L Magnum in 1993. Changes were made to improve the engine in output, reliability, and sealing against oil leakage. Chrysler succeeded on all three counts with revised cylinder heads, modern MPI fuel injection, and greatly improved assembly gaskets and seals. These revisions were enough to put the 5.9L Magnum at a competitive power level and bought the basic engine platform another 10 years of production life in Chrysler's popular truck, van, and SUV offerings, until it was ultimately replaced by the 5.7 Hemi.

Mopar Performance's older 300hp Magnum crate engine was a basic 5.9L Magnum production engine, delivered with a two-plane intake manifold, a car oil pan, and conventional electronic ignition for retrofit applications. The rest of the hardware is the same stuff found in hundreds of thousands of these mills installed in truck applications from '93 and up. How do these Mopar Magnum 360s respond to mods? We loaded one onto the dyno at Westech to find out.

For a baseline, we installed a Mopar Performance M1 dual-plane manifold. When dealing with a production Magnum in a retrofit application, in most cases the factory MPI will be replaced by a single four-barrel intake.

Owing to the crate-engine origins of our test motor, this Magnum was already equipped with an earlier LA-series timing-case cover and conventional early water pump. We cobbled the drive from a 215 Buick crank pulley and aftermarket water-pump pulley for a slight underdrive. Salvage-yard Magnums have serpentine accessory drives and reverse-rotation water pumps. The early case and pump are a bolt-on swap.

When considering low-buck performance for a Mopar, good power potential and ready availability make the 360 a winner. However, the days of buying a good used but serviceable LA-series 360 to swap are drawing to a close, and even good cores are getting harder to find these days.

The later Magnum-series engines open the door for a number of possibilities. It isn't a problem to find a decent used 5.9 Magnum engine from late-model used-parts sources, ripe for whatever performance plans you might have. In fact, Magnum mills seem to have survived the rigors of service much better than the earlier engines, owing to improvements like a better ring pack with thinner moly rings and effective MPI fuel injection with modern engine management, all leading to a reduction in bore wear. It's not uncommon to pop the lids on a 100,000-plus-mile Magnum and discover negligible bore wear, while the older carbureted small-blocks would have been spent. Good bores and a sound engine are essential to the foundation of a low-buck performance engine.

So what kind of power is lurking in one of these late-model Magnum 5.9 engines? Some time on the dyno answered that question, but first we needed a suitable test mill. The most common approach here would be to salvage a core or used engine from a late-model truck, van, or SUV, but we took the easy way out and shortcut the process by using a 300hp Mopar Performance crate engine as our dyno mule. Before you cry foul, consider the origins of and equipment on this basic crate offering.