Adam Auerbach’s 780 HP GMC Syclone Track Day Beast Eats Porsches

Many automotive infatuations begin at an early age and are never truly relinquished. In building his utterly unique GMC Syclone Adam Auerbach’s hearkened back to college and his friend’s Buick Grand National when the two would take the inconspicuous black coupe around town in search of Mustangs to surprise.

Fast forward a couple years, and a recently graduated Auerbach went looking to satisfy that urge that the turbocharged Buick instilled not long before. Fortunately, a new truck that had recently hit the market had an odd combination of qualities that could take him back to his college hellraising days. With a small loan, he picked up a GMC Syclone. In 1991, the Syclone was the quickest production truck in the world; it could sprint to 60 in 4.5 seconds and finish the quarter-mile in under 14 seconds. Even with that level of performance, Auerbach was looking for more.

From the start, the aim was to make the rare and understated truck faster stoplight to stoplight. With the addition of a custom EPROM in the OEM ECU, a catback, and a smattering of breather mods, the factory-modified LB4 4.3-liter V6 (RPO Code Z09) made out roughly 350 horsepower at the wheels—all of which it could use thanks to four-wheel drive. This bump in power was enough for a 12.5-second run at 103 miles an hour, which satisfied him until the 100,000-mile mark, when the gearbox began to slip.

After chewing up a set of 700R4 gearboxes, he took a step forwards with a built, computer-controlled 4L80, but even that started to protest not long after. “At that point, it became clear that it wasn’t reliable enough for road usage, so I went down the dedicated race car route.” Wise man.

Building a Pretty Fast Pig

When considering the truck as a potential road course machine, there’s very little that the Syclone brings to the table after the drivetrain is considered. Poor torsional rigidity, a high center of gravity, 65% of the weight sitting over the front axle, the aerodynamic properties of a brick, and the near impossibility of putting a functional cage inside the cramped cab meant there was little to make it an agile road course car. However, Auerbach relished the engineering challenge; saying, “You can’t make a pig into a race car, but you can make a pretty damn fast pig!”

With minimal lag and reassurance from the four-wheel drive, Auerbach’s Syclone was effective at the dusty Virginia City Hillclimb.

A talented mechanic, he was able to fabricate most of the pieces needed, and with those he couldn’t, he brought in skilled fabricators with Alchemy Research & Development. To keep the car from folding like a pretzel during acceleration and hard cornering, he’d need to stiffen the chassis and plant all four tires firmly on the pavement. First, he installed a cage in the car, and welded it to the shock towers.

Of course, the footwork was in need of serious modification. First, with help from people experienced in trophy trucks, the Syclone was slightly overbuilt for the requirements of road racing. In the rear, a custom three-link was installed, then rearranged all the mounting points for the front suspension in an effort to dial in more camber and caster.

With a new foundation laid, he added chromoly arms, a set of Ohlins custom-valved coilovers, Hyperco springs, and tubular anti-roll bars to keep the Syclone squat and upright in the middle of a quick corner. Those springs and dampers, in conjunction with lightweight, three-piece BBS racing wheels with magnesium centers and aluminum outers. Measuring 17 x 11″, these wheels are wrapped in 315-section Nitto NT01 gave the truck the grip and athletic stance it needed.

To bring the Syclone to a stop, Auerbach opted for Baer/Alcon four-piston brakes in front and 13.5″, two-piece rotors with aluminum hats. At the rear, a set of standard C5 brakes do the job. 

A Beefier Driveline

The beauty of four driven wheels and a stout powerplant meant usable horsepower was always on the horizon. However, the addition of a Tremec T56 necessitated a lot of custom tailoring to fit the four-wheel drive system. After installing a built T56 nicknamed “Tranzilla” from Rockland Standard Gear, Auerbach had custom 32 mm input and output shafts put into the BorgWarner 4472 transfer case. Now, he’d have control over the motor and all of its power, which would still be sent to all four tires.

Now lacking a torque converter, it had to be slightly overbuilt to handle the shock loads from the manual shifter. With some help from the forums, he devised a fairly simple way to get the stout transmission to work. After taking off the tailhousing from the T56, he replaced it with the transaxle tailhousing from a C5 Corvette, and with a homemade adapter, he bolted it to the BorgWarner transfer case. It fit perfectly, and didn’t even require new driveshafts.

Doubling the Power Output

The 4.3-liter LB4 engine was was primed for replacement, and with so little space to work, the easier part was selecting the right components. First, Auerbach sourced a now-discontinued GM Performance Aluminum Bow Tire Block, which at 75 lbs. weighs less than half the weight of the original iron block. With a 4.03 inch bore and a 3.75-inch stroke, the engine now displaces 287 cubic inches or 4.7 liters. The rotating assembly includes 6.0-inch Cunningham connecting rods forged from 4340 chromoly steel,  along with inverted dome JE pistons for a compression ratio of a turbo-friendly 9.5:1. On the breathing side the build started with Brodix high-flow V6-10 aluminum heads, cast from the same A356-T6 aluminum as the Bow Tie engine block. Valves are operated via a custom C43 hydraulic flat tappet grind from Comp Cams.  Jesel Pro Series Aluminum Rockers open and close Ferrea 2.08-inch intake and 1.60-inch exhaust valves. For fuel delivery, a Holley EFI system is feed by two Bosch 044 pumps, and a sequential ignition system from EFI Connection was put in charge of delivering the spark.

By relocating the radiator, fans, and Accusump system, he was able to shoehorn the engine and turbo in the cramped bay.

Though there was very little room for a larger turbocharger, Auerbach shoehorned in a ceramic ball bearing-equipped Precision 6766 turbo with ceramic ball bearing-equipped that delivers 20 lbs. of boost, mated to a TiAL blow-off valve, provided the whooshing soundtrack and enough air for over 600 horsepower distributed among all four wheels. With its rational compression ratio, equal length tubular headers from Alchemy Motorsports, and its 4.7 liters of displacement, the turbocharger spool is almost nonexistent—perfect for the road course—and the hydraulic valvetrain allows for a broad powerband with a 7,500-rpm redline. In the end, the package produces 650 wheel horsepower with 777 lb.-ft. of torque, plenty of fireballs, and enough grunt for a 10.3-second pass in the quarter-mile. In fact, our ‘guesstimator’ calculates flywheel horsepower at nearly 800 horsepower.

A Truck With the Track Car Treatment

Even with the improved rigidity, added stick, and doubled power output, the Syclone was still very much a truck. To make it better suited to the road course, a diet was in order. The Bowtie block shaved eighty pounds off the nose, and the fiberglass front fenders, aluminum inner fender wells, a carbon hood, and aluminum skeletonized radiator support also helped in that regard. In total, these slimming measures drop the 600 pounds, resulting in an overall weight of 3,000 pounds—quite svelte for a tech-heavy truck with a rollcage.

Weight loss was only part of the build’s objective—shifting the weight rearwards was another. Since the front mounted intercooler took up all the real estate in the front of the engine bay, Auerbach realized he needed to relocate the radiator, battery, and Canton Accusump to the rear. Two SPAL fans feed the Ron Davis dual-pass radiator, which is attached to an oil cooler. A Fuel Safe eighteen-gallon fuel cell with Kevlar bags sits behind them, and contributes towards the overall handling balance. Though some heft is added with the cooling and fuel modifications, the upside is that 6% of the overall weight is shifted towards the rear—resulting in a balanced 57/43 split.

Inside, the cockpit was made spartan and focused for the job. Racetech RT4000W seats, a MOMO Mod 80 wheel, and a Racepak IQ3 dash and datalogger are all Auerbach engages with. Even the cage is neatly tucked away to allow for some maneuvering space inside.

Not only has the interior been simplified, but a CANBUS system relaying information to the Holley EFI removes the weight and complexity of the original wiring harness.

Compensating for a Brickish Shape

“The truck uses brute force aerodynamics,” Auerbach begins. Due to the truck’s boxy shape and the torque of the motor minimizing drag was something he never wasted much time with—he used the thrust of the engine to push the brick through the air. However, he never neglected the importance of downforce, and designed a few home-brewed aerodynamic elements with the assistance of Alchemy Research and Development.

In front, a broad splitter crafted from marine grade plywood extends all the way back to the oil pan. Just behind, the air pressure in the engine bay and wheel wells are vented through custom vents. Further behind, the bed-mounted aluminum sheetmetal radiator ducting funnels air back to the radiator, and past the rear axle sits a massive wing, which was plucked off a GT3 car. This hodgepodge collection of aero pieces, whose designers never imagined would one day adorn a GMC truck, only add to the appeal of this unique creation.

The vents adorning the hood were pulled from the fenders of a prototype.

The end result is a racer that is well balanced, with a generally neutral feel, if not a hint of understeer during turn-in. While the torque steer is enough to lift the nose under throttle, Auerbach’s grown comfortable with the truck’s idiosyncrasies. On R-compound tires, the truck is predictable, manageable, and quick enough to snag a 1:33 lap at one of Northern California’s most technical courses: Thunderhill West. It’s also made waves at the Virginia City Hillclimb, where the air is particularly thin, and turned heads at SCCA Time Trials. Auerbach was also nearly able to run down a Nissan R35 GT-R at Reno-Fernley Raceway. You can practically picture the beads of sweat on the Nissan driver’s forehead with that truck looming in his mirrors.

Few people take a truck, with all its shortcomings, and try to make it into a dedicated track weapon. However, anything with that many modifications needed can only teach the builder an incredible amount. The lengthy and ambitious build taught Auerbach how to take a dragster with the weight in the wrong place to turn well, run in hot temperatures, and make a mockery of Corvettes and Porsches. However, he still has a regret or two. “If I could do it all again, I would have built it all around a tube frame,” he chuckles.

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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