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This Hellcat-Swapped 1968 C10 Is "An Exercise In Restraint"

Author: Bradley Iger | 03/30/2021 < Back to Motor Life Home
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“I guess it goes all the way back to my dad,” says Jody Holdren of Santa Clarita, California. “When it came to his cars, his motto was basically, ‘Why pay somebody to do something that you can do yourself?’”


During the heyday of the San Fernando Valley’s street racing scene in the early 1980s, Holdren spent his teenage years squaring off at stoplights with other would-be misanthropes in his 360ci-powered ’73 Plymouth Road Runner. He later stepped up to a ’70 Barracuda in 1987, a car which underwent a decades-long transformation under his care. “First it was a 14-second car, then a 13-second car, then 12s, then 11s,” he explains. “Eventually we stopped at low 10s. A lot of paychecks went into that car.”


By 2010 it was motivated by a stroked, 496-cube big-block, as Car Craft Magazine documented in April, 2010, and it was more of a race car than street car by Holdren’s estimate. Eventually he found himself wanting to build something else that would be more of a cruiser; a vehicle he could drive every day if he wanted to. That got him thinking about a vehicle that had been near and dear to his heart in his youth. “When I was 17, I bought a C10 off of a friend of mine for two grand, and the girl I was dating at the time really liked that truck,” he tells us. “But I ended up trading that truck to a friend, who then sold it to someone else that went out and crashed it. That really upset me – I’ve had a lot of vehicles since then, but I always really liked that truck.”

As luck would have it, that relationship from Holdren’s teenage years was rekindled in 2012, and it inspired him to seek out another C10 to wrench on. “I found one on Craigslist in Fresno and went up there with cash in hand,” he says. “When I got there, it was a total basket case. But I had a trailer and a buddy with me, and I really didn’t want to go home empty handed.”


Hoping for a miracle, Holdren drove around in the farmlands north of Fresno and happened to spot a 1968 short-bed Fleetside gathering dust alongside an array of old Detroit iron in a mechanic’s yard. After tracking down the owner he struck a deal, and Holdren headed back to LA with the truck, an extra cab, and bed full of extra parts. “It was in pretty rough shape – you could stop this thing Flintstones-style by sticking your feet through the floorboards,” he says. “It was a project that had never really been started, which is why he had the extra cab and all of those parts, but he just hadn’t ever gotten around to it.”


He says he had initially planned to keep it largely stock, but we all know how that goes. “I was just going to leave the straight-six in there, but it was pretty worn out,” Holdren notes. “So I got my hands on a Chevy small-block and an overdrive transmission, and I threw some aftermarket heads on there, along with a few other things. I was starting to fix it up.”


Hellcat GMC engine bay

To provide additional clearance for the big Hemi in the GMC’s engine bay, Holdren sourced exhaust manifolds from a Grand Cherokee SRT8, which were designed to fit into the tighter confines of the Jeep’s engine bay in comparison to its Dodge and Ram brethren.


Looking to improve the truck’s drivability, Holdren began looking into EFI conversion options when a friend of his came across a 6.4-liter Gen III Hemi and suggested that as an alternative. “I’m a Mopar guy at heart, and I’d never seen a 392 in a C10 before, so the idea was intriguing.”


He quickly set to work getting the Hemi and its 545RFE five-speed automatic to play nice with the GM chassis and electronics. “The truck came with a factory low hump, but once I put a high hump in it, I had all kinds of room for the transmission. Other than that, I didn’t have to cut the frame or anything like that. A friend of mine has a shop with a plasma table, so we fabricated the motor mounts there. I put the Hemi and transmission in there, kind of where I wanted it in the engine bay – back and low – basically resting on a sandbag on top of the cross member. I figured out where I more or less had an inch all the way around it, and we made the mounts from there.”


Holdren was up and running after he sourced a harness and ancillary electronics from Hotwire Auto to get the modern Hemi to work with the vintage GM hardware, but it wasn’t long before he was looking for ways to liven up the truck even more. “I started wondering what would make it more fun,” he says. “And that’s when I got the Tremec six-speed manual gearbox and the factory clutch.”


Hellcat GMC interior

The custom seats and buddy bucket come from TMI Products. A Hurst shifter helps to maintain the vintage vibe while delivering short, positive throws.


He drove the C10 in that configuration for about a year before the itch to step things up struck once again. “That’s when I saw the Hellcrate. I figured that since I’d already done all the work to get a modern Hemi to work in this truck, everything would just bolt up, and this crate motor came with the Hellcat clutch. It also just so happened that the day I saw the Hellcrate was the same day someone called me and asked if I had a 6.4-liter Hemi for sale.”


After dropping in the new Hemi, Holdren swapped in a smaller supercharger pulley from the folks at HellRaiser, along with larger injectors, and sent the truck over to the folks at OST Dyno for tuning, where it made 745 horsepower at the wheels – or about 800 at the crank.


Hellcat GMC rear axle

Power is sent to the rear wheels through a 35-spline Currie 9-inch with 4.11 gears. “At 80 mph on the freeway, the engine is doing about 2000 RPM – it’s perfect,” Holdren says. The C10’s burly rumble is provided by a mandrel-bent three-inch exhaust system with a pair of Flowmaster mufflers.


While the C10 is long way off from the mild-mannered straight-six project he took on back in 2012, Holdren says he’s gotten better about knowing when a project is “done” these days.


“I really just wanted to make it into something that was quick and handled well, but that I could also drive anywhere,” he says. “It’s got air conditioning, it’s got heat. But it’s also the most powerful car I’ve ever owned and it gets 17 miles to the gallon on the freeway. At this point I feel like there’s not much more I need to do to it – I feel like I built it right the first time.”


Hellcat GMC Suspension

The low stances comes by way of an Accuair air bag suspension system with Viking double-adjustable shocks at all four corners, while NASCAR-style front and rear sway bars from QA1 keep body roll in check out on the twisties.


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