How To Build A Better Boss 302 Engine

Sometimes we stumble onto engine projects in the darnedest ways. In this case, we have a Boss 302 that has been sitting around for more than a decade in at least four different machine shops, as well as in my garage. It's a good example of how not to plan and execute an engine project. The engine has been consuming more than its fair share of space lately, so it became a priority.

Our Boss 302's cylinder walls needed finish-honing to accommodate standard-bore Speed Pro forged pistons. Jim Grubbs gave our bore a crosshatch pattern for good oil control and proper ring seating.

Always hone lifter bores for the same reason you hone cylinder walls: oil control and smooth operation. At home, you can use a brake cylinder hone on lifter bores.

It belongs to Ron Bramlett of Mustangs Plus in Stockton, California. He initially wanted to build this engine for one of his race cars. After one of my visits to Mustangs Plus, Ron drove me and his Boss 302 engine to Los Angeles. We dropped it off at a local machine shop, which sleeved the block and did much of the machine work. I eventually hauled it to other machine shops where there were several false starts but no progress.

Most of the delays were rooted in hard-to-find parts. A Boss 302 engine isn't the same as the average 289/302. It has a four-bolt main block, a steel crank with a 3-inch stroke, and C3AE-style 289 rod forgings with broad shoulders and larger 3/8-inch bolts. Although the Boss 302 uses 351C head castings, they have different cooling passages. It also uses a unique dual-plane, high-rise intake manifold, which was an issue for us because we didn't have one.

Bores are chamfered to enable smooth piston/ring installation. Our block has been line-honed and decked for perfect fit top and bottom.

Does your machine shop use a torque plate for cylinder honing? If not, find another machine shop. Torque plates are bolted on top of the block to simulate cylinder-head installation to get cylinder bores true to what they'll be with the heads installed. Honing the bores without a torque plate is trouble because when you install the heads, cylinder bores will distort, creating ring-seating issues and abnormal wear.

Ryan sets the Scat crank with a 3-inch stroke-that's right, 302 ci. We could've stroked this Boss 302, but we wanted to retain its high-revving qualities. Ryan set the bearings and splashed on engine-assembly lube. Once the crank is set, Eric snugs the main caps. He'll torque them in thirds: No. 3 cap, No. 1 cap, No. 5 cap, then Nos. 2 and 4 caps. With each torquing, he'll check the crank for freedom of movement. He should be able to turn it with his fingers right up to final torque. If it becomes too tight, clearances are in error.

When I told Jim Grubbs of JGM Performance Engineering about the engine, he offered to build it. He thoroughly inspected the C8FE Boss block and D0ZE head castings. Everything checked out. Our block had been successfully sleeved and remained leak tight. Jim measured the bores and pistons, concluding that the block needed needlepoint machining and blueprinting. Our Crower Sportsman rods were ready for inspection and massaging, and Ron's Scat crank with 3-inch stroke was sent to the balancer along with pistons, rings, bearings, rods, a 28-ounce Centerforce flywheel, and a Fluidampr harmonic balancer.

When you build an engine, whether it's a stocker or a high-revving screamer, blueprinting should always be done. Professional engine builders teach us that it's important to look at your engine and see things you've never seen before. Never install parts right out of the box; always inspect and massage them as necessary.

The Block

We have an early Boss 302 block-technically, a 302 Tunnel Port block cast December 5, 1968 and used for a production '69 Boss 302 Mustang. Based on the VIN stamped on the back of the block, 192845, it was originally produced for 9F02G192845. According to the Boss 302 Registry, the car survives in Medford, Oregon.

Boss 302 blocks have screw-in core plugs, also known as freeze plugs. According to Jim, never try to remove them. Screw-in plugs coupled with four-bolt main caps are what separate a Boss 302 block from other small-block Fords.

One-Piece Seals

We're doing something sacrilegious by converting an early Boss 302 block to a one-piece rear main seal. Ford used a two-piece rear main seal in all of its engines until 1982. Installed properly, it works well but eventually leaks. Ford and the rest of Detroit went to one-piece versions to eliminate that problem. Converting your small-block to a one-piece seal is easy when it's performed during a rebuild.

Going to a one-piece rear main seal involves cutting the block with the same equipment used for boring cylinders. Jim cuts the lip out of the main cap used to retain a two-piece seal. Once the lip is cut, the No. 5 main cap will accommodate a one-piece seal. The lip must be machined off the crank as well. This is an easy task for any machine shop.