In the early 1960s, Ford had seen the ascent of the Chrysler Hemis in the racing world and was eager to level the playing field, perhaps tilting it in their favor. They put their collective noses to the grindstone and delivered one of the most aggressive engines of the era with the FE-based 427 Cammer. It was strong enough to bring home NASCAR's manufacturer's title for 1964, but was subsequently banned from competition in 1965. There was a good amount of backroom brawling about the Hemi and the Cammer, and in the end, NASCAR pretty much said the SOHC engine was too high tech and was never offered in an actual production vehicle, so they effectively banned it. Not willing to take the hit lying down, Ford fought back with a vengeance. In 1969, after carefully reading the NASCAR and NHRA rulebooks, they came up with an engine design that smacked the rest of the racing world square on the nose. The Boss 429 "Shotgun" engine was born.
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.
To say they were "showcasing" their heads is probably an understatement. With over 850 horses on tap, their 534-cube Boss destroyed most of the field, easily landing the team in the top half of their very first EMC trial. Team leader Simone was obviously pleased, and credited cylinder head designer and team member Miller with creating an incredible cylinder head as their jumping off point. A mold and pattern maker by trade, Miller had no problem creating a casting that was as visually stunning as the original, and had the advantages of modern casting techniques and materials.
After the initial warm-up, the engine was shut off, but a little too much heat in the chamber caused it to diesel on and spin backward for a few seconds. This mishap blew out a carb baseplate gasket, and the guys had to dip into their tuning time to get it corrected. Like they say, that's racing.
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."
Combining improper assembly with a weakened casting is a natural recipe for making the original O-ring gaskets fail, and it only made sense to fix these potential problems all at once. Miller personally oversees the production batch runs of the new heads as they are cast in Iowa at a top-notch foundry. The redesign of the head bolt supports, head gasket sealing, material, and heat treat make the heads a perfect match for those wanting to restify a '69 Mustang into a Boss clone. The heads as seen on their YouTube dyno video produce a bolt-on package good for over 700 horses with their "Classic" heads. For those wanting even more, TM also makes what they call their "430" version, with a high-efficiency combustion chamber and revised ports that flow over 430 cfm out of the box. The ShotgunHemiParts.com team used a set of those "430" heads as their starting point and continued with their induction system design.
A week's worth of work is seen once the carb is lifted off the intake. Simone altered the shape and size of the plenum to match the size of the engine, the shape of the runners to match the heads, and the diameter of the runners to match the rpm range. It all has to click just right to make this kind of firepower.
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
A common trick with Top Alcohol and Top Fuel pistons is to hard anodize the entire piston, creating a surface that better disburses heat and reduces microwelding to the rings. Simone went ahead and anodized the pieces, but was unsure whether or not it would be possible to add a Teflon coating to the skirt that had been anodized. It turned out to be the perfect surface to add a coating.
The stock-volume, stock-pressure pump was a base-model Melling design that was blueprinted to verify it was to spec. A full-length windage screen sits down in the oil pan helping pull oil from the spinning crank. The oil system is otherwise just as nature intended.
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.
Keeping the valvetrain stable in the hemi starts with a set of bombproof COMP lifters motivating some mondo 1/2-inch diameter Trend pushrods. Simone, along with a majority of engine builders, is of the school that stability on the pushrod side of the valvetrain trumps weight reduction, and with intake valves almost 21/2 inches wide, he needed all the stability he could muster. Even with all the bases covered, the .800-inch lift cam killed a valvespring on the first competition pull. That's right, this thing was making 855 horses with only seven candles lit!
Lighting the candles in a machine with this much cylinder pressure calls for an ignition system that is stout, but still easily adjustable. The ShotgunHemiParts.com team agreed on using an MSD Programmable Digital 7 box along with their HVCII coil and Pro Billet distributor. Using the Digital 7 allowed the team to custom tailor the ignition curve up or down based on engine rpm, and also has the ability to individually adjust the timing on each cylinder separately if a dual-sync distributor is used.
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."
BY THE NUMBERS ShotgunHemiParts.com 534ci Boss Ford Bore: 4.444-inch Stroke: 4.300-inch Displacement: 534 actual cubic inches Compression ratio: 11.4:1 Camshaft: COMP Cams solid roller Cam duration: 254/246 degrees at .050-inch lift Valve lift: .800/.800-inch Rocker ratio: T&D Machine 1.75 ratio Top ring: .043 Total Seal stainless steel Second ring: .043 Total Seal Napier Oil ring: 3/16-inch Hastings low-tension Piston: Diamond custom Block: OEM cast-iron C9AE-E Crankshaft: Scat 4340 forged Rods: Scat 6.800-inch H-beam Cylinder head: TM Enterprises Boss "430" Intake valve diameter: 2.45-inch Exhaust valve diameter: 1.875-inch Intake manifold: Weiand tunnel ram Carburetor: Holley 4375 Dominators (two) Header: Gilsbach Racecraft 21/4-inch primary Ignition: MSD Digital Programmable 7
DYNO DATA BEST QUALIFYING PULL RPM TQ HP 3,000 623 356 3,100 625 369 3,200 619 377 3,300 610 383 3,400 600 389 3,500 590 393 3,600 582 399 3,700 579 408 3,800 584 423 3,900 599 445 4,000 618 470 4,100 633 495 4,200 648 518 4,300 660 541 4,400 668 560 4,500 674 578 4,600 675 592 4,700 683 611 4,800 697 637 4,900 713 665 5,000 724 689 5,100 732 711 5,200 740 733 5,300 746 753 5,400 749 770 5,500 747 783 5,600 744 793 5,700 741 804 5,800 738 815 5,900 732 823 6,000 727 830 6,100 719 835 6,200 711 840 6,300 705 846 6,400 698 850 6,500 689 852 6,600 679 854 6,700 670 855 6,800 659 853 6,900 645 847 7,000 634 845
