Dale Amy
July 25, 2007
Photos By: Ford Racing

Horse Sense: Watch out for the episode of Overhaulin' in which we convert a '70 Mustang Sportsroof into a Boss 302 clone. Part of the build includes the car receiving a new engine based on the Boss 302 block from FRPP.

The more seasoned among us and even the majority of younger readers will have some memory of the rev-crazy '69 and '70 Boss 302 Mustang. A street car built, more or less, to homologate a Trans-Am race engine, the Boss' revered reputation among Fordophiles was firmly founded upon a tough nut of an engine block featuring sturdy bottom-end bulkheads, four-bolt main caps, and screw-in frost and oil gallery plugs. The lightweight 5.0 blocks issued in factory Fox or SN-95 Mustangs absolutely paled in comparison.

"Boss 302" is a fitting designation for Ford Racing's latest-and greatest-cast-iron 5.0 engine block. Though it pays due homage to the late-'60s original, the new Boss 302 block is a tougher and more advanced piece than even the stalwart Ford Racing Performance Parts R302.

Naturally, that's all ancient history. In recent years, Ford Racing's catalog has carried two variants of 8.2-inch-deck cast-iron 302ci blocks for those in need of stouter stuff than their factory 5.0 bottom ends could offer. Those offerings are the $1,050 M-6010-B50 block and the $1,995 M-6010-R302, a sturdy piece cast for Ford Racing Performance Parts by an outside contractor. But when the dwindling current stocks of the strong B50 Sportsman and stronger R302 blocks run out, they will both be replaced by the new, and stronger yet, M-6010-BOSS302 block. These are being cast-as we speak- in the same Indianapolis facility that pours the PowerStroke diesel blocks. In fact, the high-tin alloy used for the new Boss 302 block is exactly the same as found in the diesel blocks, for reasons of vastly improved tensile strength and hardness. The Boss blocks are also specifically heat-treated in order to gain the best metallurgical properties.

The Boss 302 nomenclature is more than just nostalgia; the new block bears more than passing resemblance to the original's girder-like bottom end. Yet the four-bolt main caps (on journals 2, 3, and 4) of the new Boss use splayed outer fasteners-a stronger configuration than the parallel outer bolts on the original Boss 302. The old and new Boss also share screw-in freeze and oil-gallery plugs.

One major departure from the old Boss design-as well as that of the B50 Sportsman-is the new Boss 302 is of Siamese-bore design. The production-based blocks used traditional water jackets. Aside from obvious rigidity improvements, the Siamese construction provides more meat between the holes to safely allow a larger finished-bore dimension (up to 4.125 inches).

The outgoing R302 block is also of Siamese design, but lacks the new Boss' drilled coolant crossover holes between bores. These holes provide improved cooling by reducing or eliminating steam pockets-maybe not critical on a drag application, but certainly welcome on a street, road-course, or roundy-round car. Of course, such coolant holes can be-and often are-drilled into the R302 by savvy builders, but at increased machining cost. With the Boss 302, you get 'em from the factory.

This is the stout business end of a rare, original Boss 302 block. Beefy bulkheads, or main webs, and four-bolt main caps on journals 2, 3, and 4 made this thing a tough hombre for its day. Note that all four cap fasteners are parallel-about the only configuration possible in mechanized production-line assembly fashion. Also visible here are the screw-in freeze plugs.

The new Boss 302 casting also incorporates revised oiling passages so that its lifter bores are pressure-lubed from both front and rear, as opposed to the rear-only arrangement on all preceding 5.0 blocks, including the R302. This is particularly useful with high-lift, mechanical flat-tappet cams in keeping the lifters and pushrods thoroughly oiled.

In all, the Boss 302 is a noteworthy improvement over even the previous cast-iron king-of-the-hill R302, and costs about 12 percent less, at a suggested list price of $1,759. This is amazing-especially considering the massive increase in iron prices in recent times-and is mainly due to the efficiencies and consistent quality of casting in an automated OEM production style, rather than in small batches from a manual-pour boutique casting facility. Ironically, the diesel-tough, high-tin iron alloy of the Boss flows better into the casting molds, aiding greatly in that consistency.

According to Ford Racing sources, the rejection rate on the Boss block is a mere fraction of the R302's. From Indianapolis, the heat-treated Boss blocks then trundle up the road to the Detroit suburb of Sterling Heights, where machining takes place at the same highly automated facility that machines most of Ford Racing's other blocks (see sidebar).

Despite the modular V-8's absolute dominance in current production vehicles, the new Boss 302 block-and the crate motors based upon it that will in all likelihood follow-proves that Ford Racing has no intention of abandoning its pushrod, small-block roots. In fact, about 55 percent of FRPP's crate engine sales are 302-based. The Boss is indeed back.