534ci Boss Ford Motor - Eight-Barrel Shotgun

Per homologation rules of the time, a minimum of 500 of these unique engines were required to be installed in regular passenger cars in order to be legal for the races as well. Ford contracted with Kar Kraft to install these redesigned "semi-hemi" 385-series engines into specially ordered '69 and '70 Mustangs, Cougars, and even some Cyclones. Unfortunately, the pencil pushers killed the budding Boss program in '71, leaving those wanting to race the hemis high and dry once dealerships started running out of replacement parts. Setting out to help solve this problem, longtime Ford fans Todd Miller, Doug Everstine, and Eric Simone recently competed in the 2009 Popular Hot Rodding Engine Masters Challenge to showcase their brand new TM Enterprises Boss Hemi heads sold on their ShotgunHemiParts website.

The heads externally look the same as the factory Boss castings, but without the Ford logo or part numbers to avoid any trademark issues. They also accept all of the OEM parts and accessories such as rockers, valves, and valve covers. To update the heads, Miller's design eliminated the use of the O-rings to seal the combustion chambers. Simone discussed some benefits of the new TM castings: "They use a modern gasket that we modify and sell as a complement to the cylinder heads. We eliminated the copper ring dry deck thing because the original heads had two problems. One, Ford did not reinforce the head bolt columns well enough. They didn't put enough material there and they back up right against a water passage. The torque on the OEM cylinder heads is only 90 to 100 lb-ft, that's it. Most people see that big 9/16-inch bolt and they immediately want to torque them like a 460 to 140 lb-ft. The problem there is you crack the head or you bend the head." The second weakness that TM Enterprises addressed was the material itself. "The aluminum that Ford used was high-quality aluminum for the day. The problem was the heat treat process. There's probably not a set of original heads out there that isn't bent in some fashion."

The only aftermarket intake currently available for Boss heads (keep your eyes on the ShotgunHemiParts.com website) is the old Weiand PN 1990 tunnel ram. Simone was fairly happy with the base design of the intake, but wanted a different plenum for the top, so he looked around and scored a PN 1924 top plate for a big-block Chevy that bolted right up. The larger plenum worked better for the added cubic inches that the engine picked up. Even so, Simone claims to have 40 to 50 hours invested in making the plenum to the shape he desired, and introducing 1 degree of taper from the plenum opening to the cylinder head entry. Tailoring the length of the runners to the opening point of the plenum and adjusting the average diameter of the runners from the entry to the bowl area is a key design element in making power in a specifically targeted rpm range. Short runners tend to peak higher, and longer runners tend to favor a lower rpm range. Also, a greater amount of taper in the runner, say 4 or 5 degrees, would tend to be used in higher-rpm engines, where 0 to 1 degree of taper would do well with an engine built for more midrange power. Sitting between the top of the intake and the carbs is a pair of Magnaflow anti-reversion shear plates. Designed specifically for tunnel rams and sheet metal intake manifolds, the design of a shear plate keeps fuel from pooling on the underside of the plenum lid, improving the distribution and efficiency of the intake system.

The carbs in question are a pair of Dale Cubic-modified original Holley 4375 Dominators. The choke tower is a dead giveaway that these are period correct for the Boss engine. Cubic (of CFM Carburetors) suggested that the choke towers would help the air straighten out as it entered the boosters better than a newer style flat-top carb, improving the signal to the boosters down low on the big engine. Simone says his fuel curve reflected the theory as the engine was making way more than 600 lb-ft of torque at an earth-rattling 3,000 rpm.

Simone's day job at Diamond pistons allows him access to the latest innovations in piston technology, so when it came time to design the forgings (please don't call them slugs) for this build, he threw in every trick in the book, plus some. He started out with a full, round-skirt design, knowing that with the power he was shooting for, strength would count more than a lightweight design. He decided to become a guinea pig for a new skirt design by altering the ovality of the skirt. They took the traditional football-shaped design and made it more like two triangles back to back. Focusing the piston load on a narrower area of the skirt could lead to reduced friction, or a scuffed skirt after the first firing. A teardown after break-in confirmed the new design worked exactly as intended. The skirts looked perfect, and we can credit Simone with pushing the edges of the piston design envelope just a little further

Another strength-to-weight issue is brought up with the use of pin buttons to hold the wrist pins in place rather than wire locks or Spiralox. Knowing that he would be beating on the pistons pretty hard, Simone suggested that the buttons replace a good amount of the structural strength given up by boring a hole for the wrist pins. They also provide a shelf for the oil support rail.

As with the piston skirts, the Shotgun crew coated the Scat H-beam rods with an oil-shedding coating. Those rods were floating on a matching 4340 Scat forged crankshaft, internally balanced and captured with King Alecular bearings. The rare four-bolt Boss block is a factory original piece that had never been blown up, and unlike most 385-series blocks, was perfectly happy being bored .080 over. "It's a typical C9AE-E casting and it's a service block. It's not an HP block. It's not one of the blocks that went in the cars, but it is a Boss casting with the priority oiling, the pushrod notches, and four-bolt caps." With priority oiling a standard feature in the Boss blocks, Simone says that any further oil system mods are really unnecessary. "There are no oiling system restrictors in the block. None. The oil pump is a standard-volume, standard-pressure M84D truck pump. That's it. Oil flow is an engine's life blood and if an engine is set up and clearanced properly, at least for a Boss 429, then unless you're at the highest levels of drag racing where you're over 7,500 rpm, you don't need oil system restrictors. You need to feed oil to the parts so they stay happy." They used a windage screen with an open oil pan design combined with crankshaft counterweights that were lathe-turned to keep power robbing windage to a minimum on the stroked big-block.

In the center of all the action is a COMP Cams custom solid-roller cam set up with an 8-2 firing-order swap. Simone claims that he's seen significant power gains from the swap. Simone gave a good amount of thought to camshaft design before ordering his grind. Most wedge heads tend to favor the exhaust a little more than the intake as far as duration goes. With the crossflow design of a hemi head, and a short, straight exhaust port, the hemi typically needs less duration on the exhaust. Making the mistake of installing a cam designed for a typical wedge head can lead to over-scavenging, and a big loss in power and efficiency.

The most visceral part of being near this engine under full load is listening to the exhaust as it just violently blasts through the perfectly tuned Gilsbach Racecraft headers and Magnafow mufflers. Like standing at the fence when a fuel car launches, this dual-quad Shotgun makes your chest absolutely rattle and your eyes blur! Were the guys happy with their project? Simone summed it up best, saying, "to develop a 40-year-old engine and pick up where Ford left off, that's the real appealing thing. That's the fun part about doing this."