Ken Block, co-founder of the DC Shoe company, rallycross driver, and all-around action-sports junkie, altered the world of YouTube forever when he released Gymkhana Practice in 2008. The 4-minute, 26-second display of driver skill, tire smoke, and speed—shot at the Marine Corps Air Station El Toro in California—featured Block in the driver seat of a 500hp, all-wheel-drive Subaru Impreza. Gymkhana Practice was shared around the world faster than Block killed the Subaru’s BFGoodrich tires, and it launched a 007-esque online video franchise that’s now on its seventh film.
HOT ROD was tipped off by Block’s Hoonigan Racing team that Gymkhana 7 would feature a carbon-fiber-bodied 1965 Mustang built by ASD Motorsports (ASDMotorsports.com) in Charlotte, using rally-car race chassis parts and powered by a stompy Roush-Yates V8. This new car, known as the “Hoonicorn,” was to mix the rally-car hardware Block races with the powerband and exhaust note HRM readers love in a 12-minute film shot on the streets of Los Angeles.
Four months before ASD even had a Mustang, design was underway using Solidworks. Shop owner Ian Stewart knew packaging an AWD, V8 drivetrain in a compact Mustang would be tough, so he bought a side-view line drawing of a 1965 Mustang and measured a Mustang parked on the road to double-check the drawing’s hood height, rocker height and length, and cowl location. Using those reference points, a fully-working 3-D model with suspension of the car was built in Solidworks.
The suspension was especially tricky, as the Hoonicorn was designed around a set of Tarmac R40 wheels that have quite a bit of offset in the front. The brake system had to fit inside the wheel and the suspension had to cycle within the fender flares while keeping torque steer to a minimum and allowing plenty of steering angle. Starting from scratch, Stewart designed a suspension using billet aluminum spindles and upper and lower control arms that fit the packaging and manages only 0.850-inch scrub radius.
The car that became the Hoonicorn was born as a 1965, six-cylinder, three-on-the-tree, four-lug base Mustang. It wasn’t in pristine shape, but it was relatively rust-free and wouldn’t require an inordinate amount of patch panels that could slow down the build. The firewall and floor were cut out, leaving the rockers. Because Block is tall and the Mustang is so small, the floor was lowered 3 inches to keep his helmet away from the roof. For the cage and chassis fabrication, the car was built on ASD’s 15-inch-thick honeycomb chassis plate. The plate is 12×5 feet and has a bonded steel top that is drilled and tapped with ¼-20 holes on a 1-inch grid. The plate allows ASD to build CAD fixtures that bolt to the plate and fabricate the suspension and chassis points exactly where they need to be.
Inside the V8 Tire Annihilator
ASD has worked with Roush-Yates on many late-model Mustangs built for competition, so their go-to engine was a 410ci Roush-Yates Ford small-block topped with D3 cylinder heads for a proven reliable powerplant. The heads are a previous-generation NASCAR design and are incredibly efficient at removing heat from the combustion chamber, even with restricted airflow. Stewart told us, “The engine can run at 240-250 and not care.” The heads are topped with a Kinsler stack injection that’s controlled by MoTeC EFI. A two-piece bellhousing milled from 6061 aluminum mates the Ford small-block to the Sadev (Sadev-TM.com/en) transmission. Stewart said it took around 70 hours to design, due in part to relocating the starter to clear the front driveshaft. The 2-piece bellhousing allows for quick clutch inspection.
Handling the V8s power and torque was also a challenge. Frank Rehak at The Driveshaft Shop in Salisbury, North Carolina, told us that his shop made custom CV joints for driveshafts and each axle in the car, including three for the two-piece front driver-side halfshaft. Starting with GKN CV-joints, tighter tolerances were machined in the races and cages to reduce the tendency that any spinning driveshaft component has to pick up harmonic vibrations. Because even the driveshafts of the Hoonicorn see up to 8,000 rpm.
As for the Hoonicorn’s cage, ASD had to balance safety, rigidity, and aesthetics, because the car was basically built to film, at least initially. Stewart told us, “The main goal was to make [the car] look badass and be safe.” That meant the usual 15⁄8-inch, 0.083-inch-wall tubing was used to surround Ken’s driver seat and create double door bars.
“If the flatbed or tow truck has to come get you, 9 out of 10 times I’d count whatever happened as a crash!” — Ken Block
Stewart called up an old friend, Jason Burke from Burke’s Metalworks in New Zealand, to help out on the fender flares that widen the track 5 inches on each side. The flares, air dam, and front splitter were shaped in steel first. The parts were then removed from the car, reinforced from the rear, and made into plugs for carbon-fiber panels. Stewart told us that Burke was able to hand-fabricate panels and see them on the car faster than if they’d been designed in Solidworks and machined molds, with the benefit of knowing how the final results would look. In addition, the rear flares are also carbon fiber, as is the dash and inner door panels, while the outer door skins are composite.
From Ken Block Himself
HOT ROD] Why a notchback?
Ken Block] I went with the notchback because I felt it had a more aggressive and sinister appearance. Also, my buddy [and Formula Drift driver], Vaughn Gittin Jr., had done a fastback a few years ago, so I wanted to make sure our projects were very different visually.
HR] Why a 1965 Mustang in the first place?
KB] The 1965 was chosen because it coincided with the 50th anniversary of the Mustang taking place in 2015. It’s just sort of a cool anniversary to align with.
HR] How do you like the V8 versus turbo four-cylinders?
KB] I love the engine in the Hoonicorn, the instant torque delivery is a lot of fun and really helps make the car very easy to control during Gymkhana maneuvers. I still love my Ford EcoBoost motors in my Fiesta race cars, but the V8 in the Mustang just feels amazing.
HR] Was it tough getting back into the race car after being in the Mustang?
KB] Ha! It was, actually. The first car I got into after driving the Hoonicorn was the WRC Fiesta, which only makes around 330 hp. I kept telling the engineers it felt slow and they just laughed since they knew we’d come straight from Gymkhana 7 filming.
HR] Could we convince you to race the Mustang in some other event? What about Pikes Peak?
KB] I’d love to race the car at some events, and I’d certainly consider racing it at Pikes, although it may need some boost for the altitude.
HR] Did you ever crash the Mustang during the filming?
KB] Nope, the filming went pretty well overall.
HR] What is your definition of “crash”?
KB] If the flatbed or tow truck has to come get you, 9 out of 10 times I’d count whatever happened as a crash!
HR] Will the car make any public appearances in the next year?
KB] Yes, I plan on running it at a few events globally next season. I’ll be announcing where on HooniganRacing.com sometime early in 2015.