Building New 302 Engine

A neighbor and good friend, Gary Mattson, found a steal of a deal stuffed away in a Burbank, California, driveway--it was a sleeping, low-mileage Emberglo 1966 Mustang hardtop for a thousand bucks. It was a complete C-code 289, two-barrel hardtop with an abundance of desert dust inside and out, void of rust and body damage. When the Mustang arrived at its new home in Simi Valley, research revealed a Mexican block with the original 289 Thermactor heads and intake manifold. Removing the heads showed us a 0.040-inch-over block, cast pistons, and a 1M 289 crank with C3AE connecting rods.

With the original 289 block gone, Gary became less concerned about originality, especially with a garden-variety 289, two-barrel hardtop. Building a tastefully understated restomod would be Gary’s objective for the budget Mustang. Gary wanted a durable 200,000-mile engine, but because of a tight budget, he had to examine his options. He could have taken a chance on the rebuilt Mexican-block 289 and freshened it up with new gaskets, seals, and a valve job. This may have taken his Mustang the distance--maybe. He also considered finding an original 1966 289 engine and rebuilding it to either stock or modified condition. When we began searching for a 289 engine, we learned there are fewer and fewer available cores that haven’t already been bored oversize. Gary could have sleeved a suitable core, but that would have been costly. Gary came up with an option none of us had thought of until we examined a two-page color ad in Mustang & Fords--building a brand-new 302 small-block from Summit Racing. This is one of the best bargains going if you’re capable of putting together an engine yourself.

Gary ordered a new 5.0L bare block from Summit Racing--a $260 value, plus shipping. When it arrived, we were jazzed over its newness--a fresh iron block straight from Ford's Cleveland foundry, ready for assembly. Joel Fishel at Summit set us up with a complete engine kit that included standard-size hypereutectic pistons, rings, bearings, gaskets, seals, high-volume oil pump, and a roller camshaft designed for the roller block. Larry Ofria of Valley Head Service accepted our new block and decided to check it for trueness. Because we're going to blueprint this small-block, Larry checked the main bearing saddles and align-honed as necessary. He went into his inventory and pulled a good 2M 302 cast-iron crankshaft, which would be machined 0.010/0.020-inch undersize to accommodate the new Childs & Albert rods and bearings. All eight bores were miked for trueness and honed to match the pistons.

You might be tempted to ask why we checked a brand-new block for machining accuracy. The answer is the same reason we check and recheck everything else when we're building an engine. It's easier to check and recheck something when it's apart than it is when you're sitting on the side of the freeway watching the police pour kitty litter on the oil your blown engine left in the road. Larry believes, as do most reputable engine builders, that brand-new doesn't always mean perfect. Parts aren't always properly machined, nor are they always packaged correctly. Check it now, and you'll be glad you did later. What may surprise you is the accuracy of our new 302 block right off the Cleveland engine plant's machine line. The line bore was perfect and only needed a light dressing with Valley Head's line boring machine. The cylinder bores were honed using a torque plate, which surfaced some irregularities in the bores. Honing did the trick. The decks were shaved mildly to true them up and add some compression. Oil galley plug ports were threaded and fitted with screw-in plugs. Then Valley Head thoroughly cleaned the block.

We did a lot of brainstorming on cylinder heads for Gary’s engine. His 1966 Thermactor (smog) heads were a viable option because they sport the same-sized chambers as the 49-state heads. However, the Thermactor exhaust manifold ports tend to interfere with exhaust flow and proper header gasket sealing. We tossed them on the shelf for a day when a concours restorer might need them. Larry went into his inventory and pulled out a set of 1970 302 (D0OE) heads, which sport the 58cc chambers necessary for our engine to operate effectively. He explained that the 302’s chambers are slightly larger than the 289’s, which keeps compression in the range of 9.0:1 to 10.0:1. What’s more, the 302’s chambers and exhaust ports are less restrictive than the 289’s. Translated, that means better flow around the intake valve, which is shrouded on the 289 head. Valley Head went one step further with a mild exhaust port cleanup, getting rid of the hump in the port. Valley Head installed hardened exhaust valve seats and improved the valve guides for longevity.