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Big, boosted horsepower has been a keen area of interest for Shawn Lavrick as far back as he can remember. As the owner of Twisted Speed and Performance, a Louisville, Kentucky-based hot rodding outfit that specializes in LS and Gen III Hemi combinations, Lavrick and his six-person crew have been helping a growing roster of enthusiasts take their projects to unprecedented levels over the past few years. However, when it came time to put together a truck for parts hauling and other shop-related duties, his plan was to keep things simple. Initially, anyway.
“I bought this ’71 GMC Sierra from a friend of mine, who’d had it for about a decade,” he recalls. “It started out as a shop truck build – we were just going to LS swap it, make it something we could use to get parts and that sort of thing. But when we started digging into the project, we discovered that the frame was bent, and it just kind of snowballed from there.”
Shawn Lavrick, owner of Twisted Speed and Performance in Louisville, Kentucky originally envisioned his GMC as a basic shop truck. And from the front, it still sort of looks like one. But beneath the classic GM sheet metal lies a radical beast that went far beyond Shawn's original plan. "We discovered that the frame was bent, and it just kind of snowballed from there," he says.
Lavrick soon decided that the best course of action was to fabricate a new frame for the truck, and that decision opened up a wide array of different options for the direction that the team could take with the project.
“When we started building the frame, it occurred to me that we could just put the motor wherever we wanted to,” he says. “And that’s when I got the idea to mount it in the bed. My guys were against it, but I told them that if the dimensions worked, we were going to do it.
“I took some measurements, then got in contact with RPM Transmissions to see if they could build a different input shaft for the gearbox we wanted to use,” continues Lavrick. “I knew that could be a potential hurdle, but it would allow us to bolt up a C5 Corvette’s transmission and rear end straight to the engine, ditching the torque tube and all of that while also getting the wheelbase where we needed it to be. Once we got that figured out, we were in business.”
Although the rest of the Twisted Speed crew wasn't originally sold on the idea of mounting the LS engine in the bed, Shawn plowed ahead with the idea. "When we started building the frame, it occurred to me that we could just put the motor wherever we wanted to," he says. Once Shawn had a plan for connecting the C5 transaxle to the engine, he was off and running with the project.
Along the way, Lavrick and his team put together some renderings of what the build would look like when all was said and done, in hopes of partnering up with some companies to support the build. Eventually they decided to change course and self-fund the project, in turn creating something that would more earnestly serve as a rolling showcase of what the shop is all about.
“Sometimes ideas just get stuck in my head, and I can’t get them out – I have to do it,” he says. “We’ve got CNC machines, plasma tables, and all of the other equipment we need to make our own stuff. The sky is the limit, really.”
The truck ultimately became a rolling showcase for the shop's capabilities. "We’ve got CNC machines, plasma tables, and all of the other equipment we need to make our own stuff. The sky is the limit, really.” says Shawn.
Since the team used a clean-sheet approach to the frame’s construction, Lavrick and the Twisted Speed and Performance team simply added mounting points where they needed to be in order to maintain the appropriate wheelbase and properly orient the front and rear suspension systems. “The whole chassis is made from mandrel-bent one and 5/8ths-inch chromoly tubing, and it’s triangulated for additional strength,” Lavrick explains.
An Air Lift air ride setup gives the truck its hunkered-down stance, while C5 suspension components are matched up with QA1 double-adjustable shocks to give the truck some cornering prowess.
The rear suspension – an independent setup also borrowed from a C5 – is mounted to a custom fabricated cradle that’s integrated into the frame. The Air Lift system’s air tanks have been mounted in the engine bay, along with the radiator, brake booster, and other ancillary components, while the engine’s intercooler is mounted underneath the cab of the truck.
The original engine bay still holds the radiator, brake booster, and other ancillary components, along with C5 Corvette independent front suspension and air tanks for the Air Lift system. The intercooler for the twin turbos is underneath the cab.
The mid-mounted powerplant is a 6.0-liter LS V8 that’s been outfitted with a Callies forged crank and connecting rods, Diamond pistons, a BTR Stage 3 camshaft, and a Holley Hi-Ram intake manifold. Boost is provided by a pair of 75mm turbos from On 3 Performance. Managed by a Holley Terminator X ECU, Lavrick says the combination is good for about 1200 horsepower at the wheels with 18 pounds of boost in the mix. The grunt is routed through a 4L60 automatic gearbox from RPM Transmissions to a C5 rear end with 3.42 gears.
“The Terminator X system was the obvious choice for this build,” he says. “We chose that one in particular because it includes the transmission control that we needed for this build. We use Holley systems on 90% of the builds we do here at the shop – they’re just easy to work with and easy to tune on.”
The mid-mounted 6.0-liter LS V8 has been fortified with bullet-proof internals to give it strength to handle lots of boost from the twin 75mm turbos. A Holley Terminator X ECU brings the whole combination together, and Shawn estimates power output to be around 1200 hp.
The team kept both the cabin and the exterior mods to a minimum. Aside from a Holley 3.5-inch display, a TCI shifter, and the reupholstered bench seat, the interior has basically been left alone. And while the truck sports a pretty wild aesthetic with the mid-mounted LS on full display, Lavrick notes that a much more conventional look can be easily achieved.
“The bodywork is basically all stock – even the bedsides and tailgate look normal, we just cut out the bed itself. The bedsides mount right up, but everyone keeps telling me to leave them off. But I also feel like the truck won’t be truly ‘done’ until it’s all together again.”
The body and interior of the Twisted Speed truck is pretty conservative, with most of the build being devoted to its unique engineering. That said, Shawn hopes at some point to give it a full show-truck finish, including a powercoated frame and a new body with good paint. But for now, he's too busy with shop work and driving the truck as-is at car shows, burnout competitions, and other events.
Built over the course of eight 40-hour weeks in the lead-up to LS Fest East 2021, Lavrick says that in the time since, the truck has competed in burnout competitions, secured awards at various car shows, and been used as a daily driver when circumstances allow. Although other projects at the shop are keeping the team busy as of late, Lavrick still has a few more improvements in store for the GMC.
“I want to powdercoat the frame and put a whole new body on it. The body will still be a ’71, but we’ll shave some stuff and give it a good-looking paint job. The rat rod thing works, but I’d really like to bring it to more of a show truck standard.”