It’s a wonderfully wacky world we car people live in. The things that turn our cranks would only puzzle those outside the fraternity. After all, who but a fellow gearhead would understand why we’re excited about—nay, salivating over—a hunk of cast iron with eight big holes in it?
The hunk of cast iron in question is the Ford Racing Performance Parts Boss 302 engine block. Just say the words ‘Boss’ and ‘Mustang’ together and you think of the infamous Boss 302 V8—the high-revving, Trans-Am race-winning motor ridiculously underrated at 290 horsepower (it made more like 400 horsepower) available for two glorious years, 1969 and 1970.
Ford Racing didn’t simply rehash a piece of Blue Oval performance history, though. The Boss 302 is thoroughly modern, designed from the outset as the ideal foundation for heavy duty street performance and racing engines. In fact, Ford Racing tapped its legion of NASCAR program engineers for design input, so you know the Boss 302 has the stuff to handle everything from supercharged street machines to nitrous drag cars and road racing.
The Boss 302 is cast from heat-treated, diesel-grade nodular iron with a tensile strength of 41,000 psi—strong stuff. The three center main bearing journals have four-bolt splayed iron caps with ½-inch inner and 3/8-inch outer bolts. Like its famous namesake, the block has screw-in oil galley and freeze plugs to increase the casting rigidity, but with modern O-ring seals to prevent leaks. These features make the Boss block plenty strong for nitrous and forced induction applications, yet it is 16 pounds lighter than the R302 block it replaced.
The Boss 302 block is capable of supporting 363 cubic inches with a bore and stroke job (4.125-inch bore, 3.400-inch crank). Ford Racing engineered extra clearance into the casting for stroker combinations—the block has ample room for crankshaft counterweights, and the cylinders are .004 inch shorter than stock to eliminate the notching you normally need to do to clear the connecting rod bolts.
Ford Racing built extra reliability into the Boss 302 block. The rear main seal is one piece to prevent oil leaks. The block feeds oil to both the front and rear of the lifter galleys to ensure adequate oiling of all lifters. The deck is drilled for ½-inch diameter cylinder head bolts (OEM head bolts are 7/16 inch); the holes are extra deep for better gasket retention and bolt clamping force. On the advice of the NASCAR boys, Ford Racing added crossover coolant holes between the Siamese cylinder bores to help remove trapped steam. Between the coolant crossover and the bigger, deeper cylinder head bolt holes, there is no excuse for popping head gaskets with a Boss 302 block, even with large shots of nitrous or blower boost.
The Boss 302 doesn’t stop there when it comes to features. Take a look at these:
• Set up for flat tappet or roller cams
• Finish align-honed lifter bores
• Large lifter bosses can be machined for bigger or offset lifters
• Provision for block-mounted engine oil dipstick
• Can use factory Fox body Mustang oil pan with special Ford Racing oil pump pickup
• Drilled and tapped hole for clutch cross shaft used on 1960s-70s Fords with manual
Like most racing-duty engine blocks, the Boss 302 has a few quirks. Instead of factory-style stepped cam bearing bores (the bore diameters get larger as you go from the back of the block to the front), the Boss 302’s cam bores are all 2.204 inches in diameter. That requires a camshaft with common-sized bearing journals. Most cam grinders can make you one of these and Ford Racing offers the correct common OD bearings. If you want to use an off-the-shelf, OE-style cam, Ford Racing has the necessary stepped bearings for that as well.
The cylinder bores come undersized at 3.990 inches—you will need to have them finish-bored and honed to the desired size. Keep in mind that since the cylinders are shorter, you have to watch overall stroke and compression height. The longer the (piston) stroke, the farther the piston will travel down the bore. A shorter cylinder means the piston will protrude further from the bottom of the bore. That can lead to issues with increased friction, accelerated cylinder wall wear, and piston ring wear as the piston rocks in the bore.
The Boss 302’s as-cast deck height is .010 inch taller than the standard 302’s 8.200 inches. You will need to have a machine shop equalize and deck the block to true each bank to the proper deck height. You will also need to use a special set of head gaskets to accommodate the extra cooling passages between the cylinder bores. These are available from Ford Racing.
So, is the Boss 302 block the right foundation for your small block Ford project? If your goal is big horsepower or big cubic inches—or both—the answer is definitely yes. Whether you go naturally aspirated, nitrous-assisted, or forced induction, you owe it to yourself to meet the Boss.
FMS-M6010BOSS302 Ford Racing Boss 302 engine block, bare casting
FMS-M6622BOSS302 Ford Racing oil pump pickup for Boss 302 block, fits factory 5.0L Fox Mustang oil pan
FMS-M-6261-R351 Ford Racing cam bearing set for common OD camshafts
FMS-M-6261-J351 Ford Racing cam bearing set for OE-style camshafts
FMS-M-6051-CP331 Ford Racing head gaskets for Boss 302 Blocks, graphite core
FMS-M-6051-S331 Ford Racing head gaskets for Boss 302 Blocks, steel core