Jimmy’s Bullard’s 1,000-Horsepower, Tube-Framed Chevrolet C10

Chevrolet C10s shouldn’t be able to move with the agility this particular example has, but when you get a few retired NASCAR men together with no rulebook to limit them, they can turn a floppy truck into an Olympic athlete. Jimmy Bullard’s squarebody C10 build was only limited by minimum weight, a moderate budget, and a deadline. Other than that, the engineers had free rein.

This C10 wasn’t designed with just speed in mind. To complicate the build somewhat, it had to lay frame, turn heads at car meets, and set respectable times on the drag strip. A tall order, no doubt, but Jimmy’s talented team turned out a truck that is more versatile than most 1,000-horsepower vehicles could ever hope to be. The revolutionary Mittler Brothers HydroShox turned out to be a key player in that versatility – combining the performance of the latest coilovers with the ride height adjustability of air suspension.

For all you squarebody lovers, this is a 1981 Chevy C10 with a ’75 grille.

A Strong Foundation

The team began by assembling a complete tube frame that could do anything they asked of it. “We specialize in building full-blown tube chassis from Chromoly and DOM,” Jimmy began. “We build everything chassis-related except for the steering rack and brake calipers, actually.”

They make the spindles themselves, too. This means that the scrub radius and bump steer is factored into the design of the suspension geometry. “That, and the Ackerman angle, is a big deal for us,” says Jimmy. As they found out, getting this big sled to rotate requires a little toe-out on turn-in.

The front suspension’s “bumpstick” is a device comprised of rubber discs, giving them the benefits of a dual-rate spring.

With such control over the design of the chassis, Jimmy went ahead and determined precisely how much weight he wanted over each axle. “For autocrossing, we found that a little more in the rear helped bring the tail around. For cone carving, we set it at 49-percent in the rear, but we’ll shift the weight forward for a little more stability when we take it to the road course.”

Yaw-Haw

To get this burly machine to pivot predictably around its central axis, they designed the rear suspension with a rear-steer design borrowed from dirt trackers. While a typical four-link rear has the bars running parallel to each other, this one has the four links opposing each other by anywhere from 30 – 60 degrees.

As the truck rolls, the lateral weight transfer pulls on the links, shortens the inner wheelbase, and encourages the tail to turn in. “If there’s too much rear steer, we can adjust that in a couple of ways,” Jimmy begins. “Either we reduce the angle of the rear bars, or we can play with the droop limiter (pictured below).”

This spring-loaded device connects the frame to the rearend via a chain, and depending on its setting, it can help lift the inside rear tire off the road. Though this might seem like it would encourage wheelspin during acceleration, the droop limiter plays less of a role once the throttle is applied and the weight is shifted rearward.

Putting Power to the Pavement

There are a few elements responsible for this squarebody C10’s surreal traction: a Wavetrac torque-biasing differential, massive wheels, and tires, as well as heavyweight tungsten axles in the rear. Though each of these axles might be around 150 pounds heavier than a typical steel piece, they help shift some of the weight rearward; something critical in using the 355-section rubber for propulsion and not a smoke show. They also had to mind the 3,000-pound minimum weight requirement. If they had to add heft to the truck, it should be added somewhere relatively low and near the rear.

MRC’s wheels have widths of 11- and 13-inches, front, and rear, respectively.

That low center of gravity is only one reason for this squarebody C10’s unusually agile nature; the massive 315-section Hoosier R7s wrapping MRC’s custom 19-inch wheels help some, too. Wilwood big brakes with adjustable bias offer raw stopping power as well as excellent modulation—the latter allowing him to transfer the weight carefully to get pointed sooner.

Six-piston brakes clamp 15-inch rotors up front, while four-pistons grab 14.25-inch rotors in the rear.

The first time out was a revelation. “I felt like it was pulling my guts out,” Jimmy chuckles. Even with quad-digit horsepower, the grip could harness that outrageous motor. For anyone not convinced, please watch the footage below:

A Motor to Match the Footwork

Being a chassis shop, they accepted they’d be better off farming out a motor. It had to be stout and rev high since Jimmy felt a higher redline would minimize the number of shifts needed on the cone-lined courses. Mullins Race Engines heard these requests and supplied Jimmy with an LS7-based engine with Ross pistons, a Callies crankshaft, and a Jesel valvetrain. That last item helps the motor spin to 10,000 rpm.

“We’ve only tested her on the autocross so far, but we’ve got VIR coming up next month and Carolina Motorsports Park sometime after that.” In the meantime, Jimmy will be reshaping a lot of opinions on old trucks with smoky demonstrations like those seen below.

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About the author

Tommy Parry

Tommy Parry has been racing and writing about racing cars for the past seven years. As an automotive enthusiast from a young age, he worked jobs revolving around cars throughout high school, and tried his hand on the race track on his 20th birthday. After winning his first outdoor kart race, Tommy began working as an apprentice mechanic to amateur racers in the Bay Area to sharpen his mechanical understanding. He has worked as a track day instructor and automotive writer since 2012, and continues to race karts, formula cars, sedans, and rally cars in the San Francisco region.
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