SUPERTRUCK!
The American Thunder S-10 Leaps Off-Road Racing Technology In A Single Bound. magine a Formula One race car careening across rocks, boulders, berms, gulleys, silt-filled washes, and rutted dirt roads. For all of its sophistication, a fragile Formula car wouldn't survive its first encounter with a shallow pothole. Now consider Vector Promotions' American Thunder S-10 pickup. A list of this innovative Chevrolet's technical specifications conjures images of a world-class race car: fourwheel independent suspension; electronic engine management; rising rate springs; mid-engine chassis design; composite bodywork. But this stateof-the-art hardware is not installed in some spindly single-seater that competes on carefully manicured circuits. This Class 2 supertruck was built for the badlands. It was conceived, engineered, and constructed to take on terrain that would stymie a scorpion. The aim of the ambitious American Thunder program was not to take "first in class" or "fastest truck" honors. The objective was to build the fastest vehicle in the desert. Period. The American Thunder S-10 has introduced a new level of technology to the HDRA/SCORE off-road series. It is undeniably a truck; its resemblance to production pickups is unmistakable. But beneath its fiber-
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glass skin, the American Thunder S10 is a purebred racer. Its chassis bristles with fabricated components, from the exquisite uprights at all four corners to its handbuilt rearend. Said one onlooker at the S-10's unveiling, "If GTP cars raced off-road, this is what they'd look like!" This super S-10 is the result of a collaboration between the Chevrolet Engineering Raceshop, Vector Promotions, and designer Bryan Kudela. Driver Larry Ragland brings 13 years of desert racing experience to the program. Co-sponsors BFGoodrich and Mobil Oil Corp. have added their technical expertise to the formidable
American Thunder lineup. This "ultimate" S-10 was constructed at Clive Smith's Vector Promotions shop in suburban Orange, California. Smith and Ragland snared the Class 7 (two-wheel-drive minitruck) championship last season with an S-10 that now seems positively primitive compared to the team's new entry. Their new contender is built to the less restrictive Class 2 rules for unlimited two-seat vehicles. Stripped of its one-piece fiberglass body and lightweight fenders, the American Thunder S-10 is revealed as a purebred racing machine.
"The Class 2 regulations are primarily concerned with safety," says Smith, a transplanted New Zealander and accomplished rally driver. "As far as the vehicle's appearance, construction, and engine, you can basically do whatever you like." The super S-10's framework is a spider web of 4130 chromemoly steel. Every tube and gusset in this complex design has a purpose. The chassis was thoroughly tested in a computer simulation before the first joint was welded. The team's championshipwinning Class 7 S-10 also provided valuable data for the chassis design. "We installed strain gauges on the driveline and accelerometers on the bumpers to accurately measure the forces in off-road racing," Smith reveals, "That information is essential when you are searching for the best balance between light weight and strength in a new design."
"The traditional method of building an off-road racer is to 'connect the dots' between the suspension mounting points with some pieces of tubing," Smith continues. "Our approach was different. This is a totally integrated package. We believe that advanced engineering is one of our team's significant advantages." The American Thunder S-10 rides on a 127-inch wheelbase, 4.5 inches longer than a production Maxi-Cab compact truck. Its one-piece lift-off fiberglass body has been subtly stretched and reshaped to cloak the unique chassis. Kudela's mid-engined design positions the all-aluminum 5.0-liter 90-degree V6 inside the passenger compartment, where it shares space with the driver and co-driver. Smith's crew widened the cab several inches to accommodate the exhaust system, pedals, and driver's feet. Jet engine insulation originally designed
to foil heat-seeking missiles keeps temperatures in the passenger compartment tolerable. Hatches in the roof provide access to the S-10's aluminum-paneled interior. The 5.0-liter V6/90 Chevrolet from Ryan Falconer Racing Engines produces over 450 horsepower with a torque curve as flat as the Mojave Desert. This heavy-duty version of the production 4.3-liter Chevy V6 features a lightweight aluminum block and a pair of free-breathing Bow Tie aluminum cylinder heads. A dry-sump oil system filled with Mobil 1 synthetic lubricant maximizes the S-10's ground clearance. When the going gets rough, Ragland relies on the instant throttle response of the V6's electronic fuel-injection to keep him and his S-10 out of trouble. The S-10's light-alloy engine and rear-mounted transmission produce 45/55 percent front-to-rear weight
Long front A-arms provide over 20 inches of suspension travel and abundant ground clearance.
The Vector Promotions crew used yards of steel tubing to construct the S-10's rugged chassis. Computer simulations were used to test the chassis design.
Team manager Clive Smith has applied his years of rallying experience to offroad racing.
Off-road driving champion Larry Ragland enters the desert wars with two powerful weapons: four-wheel independent suspension and near-equal front-to-rear weight distribution.
distribution. "A dune buggy typically has 70 percent of its weight on the rear wheels," Smith notes. "Our S-10's near-equal weight distribution will be an advantage on high-speed sections, where precise steering control is critical." A 50-gallon fuel cell is located amidships to minimize changes in the truck's balance as the fuel load is consumed. Smith regards his truck's 150mile range as a powerful tactical weapon in off-road competition. "You can really gain some time in a long race if your driver can make fewer pit stops," he comments. The heart of the S-10's chassis is an innovative torsion-bar suspension system that provides more than 20 inches of travel for the front and rear wheels. Suspension travel is the Holy Grail of off-road racing; it keeps driv-
Where's the engine? In the passenger compartment. The S-10's mid-engined layout leaves plenty of room under the hood for suspension and steering.
An elaborate system of links and pivots is the key to the S-10's rising-rate suspension.
ers and components healthy by absorbing the tremendous impact loads encountered in treacherous terrain. Designer Kudela devised an ingenious assembly of links and pivots that gives the American Thunder S-10 a true "rising rate suspension. "In off-road racing, you really want a three-stage suspension," Smith explains. "The suspension should be relatively soft at full droop. It needs to be stiffer when the truck is at its ride height, and a lot stiffer at full bump. Bryan's system gives us the ability to fine-tune the shock absorbers for these three distinct stages." A long-travel suspension subjects axles and steering links to severe changes in angle as the wheels move up and down. The S-10's elaborate slider rack steering system is driven by a Saginaw steering box mounted behind the front wheels to protect it from rocks and road debris. Drastic measures were taken at the rear in order to maximize the length of the half-shafts in the independent rear suspension. Smith's machinists carved the S-10's differential from solid chunks of steel. The intricately machined differential housing is a fully stressed chassis member. The inner constant-velocity joints are located inside the rearend spool, which carries a massive 10.5-inch ring gear. The outer CV joints are mounted outside of the rear wheels; the halfshafts pass through the wheel hubs to minimize the angularity on the joints. Four-wheel disc brakes with huge 13-inch rotors bring the American Thunder S-10 to a speedy halt. These oversized brakes seem more appropriate to a 200mph road racer than an off-road pickup. "The large-diameter tires and wheels we use in off-road racing act like flywheels," Smith points out. "The brakes have to slow this huge rotating mass. Off-road vehicles are also heavier than typical road-racing cars. An off-road racer doesn't use the brakes frequently, but he needs to be able to stop quickly. Imagine driving flat-out through clouds of dust and then suddenly seeing a huge hole in your path. That's when you need the biggest brakes you can find." Off-road trucks are the Southwest's equivalents of NASCAR stock cars. Like their Winston Cup counterparts, the trucks that compete in the
HDRA/SCORE off-road series are closely identified with the products in dealer showrooms. Just as Dale Earnhardt's Lumina race car showcases the aerodynamics of Chevrolet's new coupe, the American Thunder S-10 highlights the durability and performance of Chevrolet trucks. "The thrust of the American Thunder program is to demonstrate that a truck is capable of taking an overall win in off-road competition," says Chevrolet Raceshop engineer Terry Laise. "The goal was to construct a truck that is as close as possible to the ideal configuration for off-road racing. Most important of all, it retains the outward appearance of an S-10, with a front-mounted engine and rear-wheel-drive. We believe that we can achieve the goal of an overall win with a production-based vehicle." The American Thunder S-10 is a masterpiece of off-road art. It brings a new level of craftsmanship and engineering to the sport. But for all its functional beauty, this truck will never languish in some antiseptic museum. Its place is in the dust and dirt of the desert.
m The artfully machined differential housing is a stressed chassis member. The rear constant-velocity joints are mounted inside the spool in order to minimize half-shaft angularity.
An automatic transmission is mounted just ahead of the differential to increase rear weight bias.