Brad Bowling
August 6, 2007
Contributers: Brad Bowling

Have you ever walked up to a restaurant 10 minutes after the posted closing time only to have a nice waitress take pity and unlock the door? Usually, she glances around to ensure you're alone, hustles you in, and you feel special all day.

In 1972, Ford Motor Company officially locked the door on its Boss Mustang program after three successful years and three distinctly different cars. The Boss 302 and Boss 429 were produced as '69-'70 models, but the '71-only Boss 351 was a happy medium between the 302's road racing prowess and the 429's dragstrip dominance.

Central to the '71 Boss identity was a 351 Cleveland V-8 designated with the code "R." The Boss engine was similar to that year's other high-performance 351, the Cobra Jet, in that they both had four-bolt main caps, 2.19-inch intake valves, 1.71-inch exhaust valves, forged-steel connecting rods, an Autolite 4300-D four-barrel carburetor with a spread-bore pattern, a dual-point distributor, and a cast-iron crankshaft. To produce more power than the CJ, the Boss engine used a different combustion chamber design-the "quench" shape-that closely shrouded the valves and increased the compression ratio substantially. Other power producers were solid solid lifters, adjustable valves, a mechanical camshaft, and forged aluminum pop-up pistons. With standard ram-air induction, the Boss put out an advertised 330 hp.

Available only with the SportsRoof body, the Boss 351 also included a blacked-out hood (silver was used when certain exterior colors were ordered), a 3.91:1 Traction-Lok rear axle; a four-speed transmission; Competition suspension; power front-disc brakes; and various cosmetic upgrades such as hood-lock pins, a front spoiler, a Mach 1 grille, and a chrome front bumper. Standard Boss 351 tires were Goodyear F60x15s with white raised lettering on 15x7-inch stamped steel wheels wearing hubcaps. Chrome Magnum 500s were optional.

At $4,124-about $150 more than the previous year's Boss 429-the 351 was Ford's most expensive non-Shelby Mustang to date, and one of its quickest. Despite a shipping weight approaching 3,200 pounds, the fastback could fly through the quarter-mile in 14.1 seconds at 100.6 miles per hour according to Car and Driver, and 0-to-60 times in the sub-6.0 second range were reported.

Had it not been for a slowing American economy, rising insurance rates for performance cars, and increased government regulations concerning safety and emissions, Ford would gladly have continued the Boss 351 for several more years. Unfortunately, the company only found 1,806 buyers for the '71 Boss-compared to nearly 8,800 Boss 302s and 429s-and realized the market for premium-priced, high-performance vehicles had come to an end. Ford announced there would be no '72 Boss, leaving a crowd of hungry performance enthusiasts with noses pressed against the glass, wishing they had arrived just a few minutes earlier.

Fortunately, a few knowledgeable Ford sales people explained that the '72 Mustang order form could be used to create a Boss in all but name. Checking the box for the R-code engine-what Ford called the 351-4V High Output-bought a host of mandatory carryover equipment from the Boss, including the four-speed, a Hurst shifter, and a 3.91:1 rear axle at an additional cost of $812.

The new R wasn't identical to the '71 version, but it was close enough to make an H.O.-equipped hardtop, SportsRoof, or convertible the fastest new Mustang on the road. Compression was lower in the '72 version, although exactly how much depends on the source. Manuals list the '71 as having anywhere from 11.0:1 to 11.7:1, and the '72 falls in the range of 8.6:1 to 9.9:1. Regardless of the compression, heads with larger, open-combustion chambers and forged-aluminum flat-top pistons were responsible for the drop, which was engineered for the lower-octane gasoline blends showing up at the pumps in the early '70s. The H.O. camshaft gained some lift but lost duration to deal with the lower compression.

An accurate horsepower comparison on paper is nearly impossible because the industry was switching from SAE gross measurements (taken at the flywheel with minimal real-world accessories in place) to net (also taken from the flywheel but with pumps, pulleys, and exhaust equipment attached), which typically read about 20 percent lower. Using that formula, the Boss' 330 gross horsepower would convert to 264 net, putting the '72's advertised 275 ponies in a very favorable light. To put that into perspective in today's dyno-crazed hobby, subtract another 15 percent for parasitic loss through the drivetrain to get an approximate 233 rwhp.

As for callouts, if anything, the faux Boss wore only a subtle fender decal that announced "351 H.O. Mustang," unless it was a SportsRoof dressed out with the Mach 1 striping. Some of the cars came without stripes or a decal. The '72 H.O. package didn't include the Boss' front chrome bumper or ram-air hood.

The H.O. is so rare that we've only seen a few examples and only one or two as nice as the coupe you see on these pages. During the final days of the Big Three's monopoly of the American auto market-Feb. 17, 1972, to be exact-the Beaudry Ford dealership in Atlanta put in an order with the Dearborn plant to produce a V-8 hardtop ($2,816) with the optional R-code engine ($812), power steering ($102.85), AM/FM stereo ($191.01), console ($67.95), Decor Group ($69.79), color-keyed racing mirrors ($23.23), tinted glass ($35.94), chrome Magnum 500s ($107.59), and Instrumentation Group ($70.83). With destination and delivery charges, the sticker total was $4,425.19. With its marriage of lightest body to most powerful engine, this Medium Bright Yellow coupe with few creature comforts was built for speed.

According to the Deluxe Report from Marti Autoworks, the coupe is 1 of 2,940 Mustang coupes painted Medium Bright Yellow in '72, and 1 of 14 Mustang coupes ordered with the 351-4V H.O. V-8 and four-speed manual transmission. It was built on March 8 and released for shipping two days later.

A few months after Beaudry took delivery of its H.O. coupe, Ford permanently shut the door on its Boss Mustang program.

Last of the R-Code Mustangs
Not much is known of this H.O.'s life until it wound up in the hands of Pat Szyslowski, a restorer and collector who owned Mid-Michigan Mustang for 16 years before relocating to the temperate climes of North Carolina. Pat has had a laundry list of desirable Ponies, including several '66-'69 Shelbys (one of which he drag raced under the name "Sneaky Snake"), a couple of Boss 302s, and three Boss 351s, but the H.O. is by far the rarest of the breed. According to a Marti Auto Works report, there were only 14 coupes ordered with the H.O. powerplant.

After trailering the coupe back from its seller in Kansas, Pat fixed minor details and checked everything mechanical; otherwise, the car was ready to show and drive. The only modification the H.O. has received in its 35 years is the addition of a ram-air hood, which Pat intends to keep because it's exactly the kind of purchase he would have made at the Ford dealership parts department in 1972.

"I was really interested in the '72 when I heard about it from a friend," he tells us, "because it's essentially a Boss 351 that no one knows about. To my mind, this is the last really great car of the first Mustang generation, and it's definitely the final R-code."