Those are the pros and cons. So how does it wash out? In practical terms, the Magnum heads, as delivered, certainly aren't race heads, but they make for a nice performance street piece. Out of the box, the potential is there to make 400-plus-horsepower with a well-thought-out street 360 combination. While those power levels were possible with the early 340 heads, the chamber design of the new Magnum-when coupled with the appropriate quench clearance-provides a noticeable torque advantage and greater detonation tolerance as compared to the older design.
So what does it take to bolt a set of new Magnums on an old block? Though the heads have been around for years, we've heard urban legends about required changes, when really, all that's required is to select the correct compatible components and bolt them on. We consider it a simple conversion. Follow along as we add a set of Magnums to a hot 360 short-block and see if you agree.
Pre-Magnum LA engines oiled...
Pre-Magnum LA engines oiled the shaft-mounted valvetrain via these oil-feed passages in the block deck. The Magnum heads' valvetrain gets oil through the pushrods. If you're starting with a bare block, the oil passages in the block can be tapped and plugged. If you're replacing pre-Magnum heads on a short-block, the factory oil hole will seal against a dead end when meeting the head's deck surface. A light smear of silicone here wouldn't hurt, particularly if extra-thin head gaskets are used.
The bolts are torqued in the...
The bolts are torqued in the conventional pattern to the spec of 95 lb-ft, the same as early LA engines. Although early LA engines all have dead-end head-bolt holes, some later small-blocks have head-bolt holes that lead into the water jacket. With those later blocks, use Teflon thread sealant. Note the revised intake-bolt angle and absence of exhaust crossover on a Magnum head.
Magnum heads use bolts of...
Magnum heads use bolts of different lengths. These new Mopar bolts feature reduced 51/48-inch heads and a built-in shouldered washer-and they're dirt-cheap.
To oil the valvetrain, the...
To oil the valvetrain, the lifters must have provisions for pushrod oiling. Fortunately, 90 percent of aftermarket hydraulic lifters for Mopar applications are universal, fitting Mopar and AMC; thus, they have provisions for pushrod oiling in deference to the AMC requirement. Check the catalog part number from the cam company that supplied your lifters. If Mopar and the AMC lifters carry the same part number, you're golden. An easy way to tell is to view the pushrod cup. Nonoiling lifters (left) have a solid seat with a hole in the center that indicates the lifter has provisions for oiling.
Magnum heads carry a valvetrain...
Magnum heads carry a valvetrain totally different than older LA small-blocks. In the Magnum system, rather than a shaft mount, the rockers pivot on individual fulcrums bolted to the head and are ganged in pairs for each cylinder by a guideplate.
Stock Magnum engines used...
Stock Magnum engines used hydraulic roller lifters, which have a much longer lift body than a flat-tappet hydraulic lifter. For the Magnum head with a flat-tappet cam combination, a unique pushrod is required to make up the lifter length difference. Mopar Performance sells a 7.625-inch pushrod, PN P5007477, for this combination. Stock Magnum rockers don't have a provision for valvetrain adjustment, so with variations in milling, cam-base circle, gasket thickness, and the replacement lifter's height, the best way to be sure is to measure. An adjustable length-checking pushrod can be set to the required length until it depresses the lifter plunger .020-.040 inch with the cam on its base circle. The pushrod's length can then be measured and the appropriate length pushrods ordered. The pushrod should feature 51/416-inch ball-ends and have an oiling passage through the center.
Installing the rocker assemblies...
Installing the rocker assemblies is simple once the correct-length pushrod is obtained. Just bolt them up and it's done.
Mopar Performance carries...
Mopar Performance carries two aluminum four-barrel intakes for the Magnum heads, a dual-plane, PN P5249500 (pictured), and a single-plane, PN P5249501.
Magnum heads use a unique...
Magnum heads use a unique intake gasket, which comes from Chrysler as part of a kit, PN P4876049. The kit includes stock-type torque-to-yield intake bolts and valve-cover gaskets that are leak-proof laminated with ribbed rubber over a steel core.
We chose MP's cast-aluminum...
We chose MP's cast-aluminum valve covers, PN P5249343, to dress up the engine. With the cast-aluminum covers, the Magnum's 10-bolt attachment system, machined rails, and trick gaskets, there's no way leaks will develop.
Conventional small-block headers...
Conventional small-block headers fit with no modifications or problems. We tried our TTI step headers on for size.
To Magnum or not to Magnum?...
To Magnum or not to Magnum? For low-buck bolt-on power, the Magnum heads are the quickest way to go.