Of all the vehicles to come out of the musclecar era back in the late-'60s/early-'70s, those inspired by the SCCA's Trans Am racing series may well have been the closest link to the future of American performance cars. Back then, factories fitted "ponycar" coupes with high-winding small-blocks, close-ratio manual trannies, wide wheels and tires, and suspension upgrades so Trans Am competitors could navigate both the road courses and the SCCA's rulebook. This was in stark constrast to the big-block-powered sedans that seemed to rules the boulevards in those dragstrip crazed days.
By building a heavily bored...
By building a heavily bored and stroked Windsor engine, Jon Hallenbeck was able to achieve big-block cubes (454 of them) without the weight of a big-block over the front wheels. Extra pounds were shaved by using an aluminum Ford Racing block. Yates heads flow huge while lending the Cleveland-style appearance you'd expect under the hood of a Boss. Motec EFI feeds the mill through a single-plane manifold, and all incoming air goes through the Shaker to ensure a consistently cool charge. The ignition system uses coil packs rather than a conventional distributor, which is replaced with a cam sensor.
Yet decades later, those early Trans Am cars are probably more in tune with the current trend of car crafting than most of the legendary muscle machines that produced sales figures as impressive as their quarter-mile times. Of course, big power is as in-demand today as it ever was, but preferably when complemented by lots of grip and stopping power.
Jonathan Hallenbeck was completely familiar with the history of the old Trans Am series and the replicas it spawned, but he was also dialed in to modern levels of vehicle performance. After having owned the "White Car" '69 Camaro built by Mark Stielow back in the '90s, Jon knew that classic muscle could be made to handle a road course with the best contemporary production cars on the market. He decided to build the Ford equivalent to merge the heritage of the original Boss 302 racers with modern drivetrain and chassis technology.
Not wanting to carve up a prime example of the breed, Jon located a rust-free but completely clapped-out -70 Boss, towed it from Texas to his Maine home, and then teamed with Emery Pratt of Central Maine Mustangs to create a Mustang that would be competitive in Car & Driver magazine's One Lap of America event--a competition Jon had participated in five times prior. This meant that in addition to being adept at various forms of automotive competition, the car would also have to be completely streetable, brutally durable, and dead-nuts reliable, since the event takes place over the course of many days at many tracks, separated by many miles ... and trailers ain't allowed.
The trunk still offers a little...
The trunk still offers a little room for luggage, despite that fact that it houses the Optima battery, sound-system amps and CD changer, and 5-gallon oil tank for the engine's dry-sump lubrication system. The 27-gallon fuel cell was custom-made before such things were catalog items for early Mustangs.
Jon and Emery dismantled the Boss, stripped the shell, and set about making their modifications. It had been decided that the car would run a Yates-headed Windsor-based V-8, but fitting the engine soon proved to be a major challenge. The Yates heads are Cleveland-based, and add significantly to the Windsor's girth, but the trouble wasn't so much getting the engine in, but leaving enough room for uncompromised headers. The solution chosen by Pratt was to modify the shock towers in a fashion similar to that used on the original Boss 429 Mustangs. This solved the engine problem, but it contributed to a separate issue with the suspension geometry. In the end, it was Stielow who offered to help Jon and Emery by working the bugs out of the suspension to achieve proper bumpsteer. Mark also helped to dial-in the Motec fuel-injection feeding the all-aluminum 454-inch Windsor, and sorted out a few niggling details with the hydraulic clutch coupling the T56 six-speed trans.
As of this writing, the car has yet to hit a road course, but Jon says that's coming soon. Wisely, he didn't want to push the Boss until he was assured that it was right. Whether or not the Mustang will ever compete in the One Lap is up in the air right now, but Jon assures us that major road use is on the schedule.
Car Craft Q&A
Jon tells us he never liked...
Jon tells us he never liked the '70 Mustang's two-hump-style dash, so he swapped in one from a '70 Cougar, which was a bolt-in affair. The Cougar dash also lends itself to the custom instrument panel and its VDO gauges more freely than the 'Stang piece would have. That stock-looking shifter links to a T56 six-speed trans, which necessitated floorpan modifications, though you'd never know it. The chairs are Recaro, and the rear seat and door panels were upholstered to match.
Car Craft: What urged you to build a classic Mustang with these capabilities?
Jonathan Hallenbeck: After owning Mark Stielow's white '69 Camaro and really enjoying it, I knew that older musclecars could be made to perform like modern high-performance cars, if not better. I'm a Ford guy at heart, so I wanted the Ford version of Mark's Camaro.
CC: Did you have the One Lap event in mind when you planned the car?
JH: Yes. I've run the One Lap five times and have had a great time doing it. Stielow's white Camaro participated back in the mid-'90s and came in Fourth overall the last time it ran. I think it's a challenge to build an older car that can actually compete with the types of vehicles that enter that competition. There's some heavy hardware there.
CC: So what's next for the Boss?
JH: Well, it has only been truly "done" for a relatively short period. It was running and driving but not completely sorted. I'm not sure if I'll attempt the One Lap with it, since the rules really don't favor cars like this anymore. I will be driving the car on the street quite a bit, though, and I'm really looking forward to some open-track time.
The Details
Car: '70 Ford Mustang Boss 302
Owner: Jonathan J. Hallenbeck
Engine: Ford Racing 351W now displacing 454 ci
Heads: Ford Racing Yates aluminum; 2.10/1.60-inch valves, 67cc chambers
Induction: Motec programmable EFI, Ford Racing single-plane manifold
Camshaft: Comp Cams solid roller 0.608/0.614-inch lift and 242/248 degrees duration @ 0.050
Transmission: Tremec T56 six-speed manual
Rearend: Ford 9-inch by Currie, 3.89:1
Front suspension: Stock '70 Mustang modified w/Global West upper control arms and Total Control lowers, coilover shocks, B&D rack-and-pinion steering, altered geometry
Rear suspension: Stock-type leafspring
Brakes: Baer 14-inch front; Baer 12.5-inch rear
Wheels and tires: Fikse 18x9-inch, front; 18x11-inch rear; Michelin Pilot 245-40/18 front; 295-30/18 rear
Body mods: Stock wheel arches, fender lips trimmed and rolled; carbon-kevlar hood
Paint: '69 Shelby Gulfstream Aqua by Emery Pratt and Mike's Auto Body, Pittsfield, ME
Cost to build: "I'm glad I didn't know when I started."