Sport Truck
By Damian Geddry
Both occupants in the Mus ta ng GT we re completely dumbstruck. Before either the driver or passenger knew what had hit them, the black sport/ utility they had been tailing for the last 15 minutes had once again disappeared around a 90-degree turn and nearly vanished over the horizon. Each time they caught up with the truck the re was no more than a subtle rumble coming from a single exhaust pipe, there was no external clue as to what might be stuffed under the hood. Granted, the vehicle had been lowered and its fenders were overflowing with serious wheels and tires. but then a dropped t ruck with performance rubber is hardly unusual.
But the folks in the Mustang knew the re was some thing different about this truck. Way different. It was obviously a GMC Jimmy, and beyond the wheels, tires and some modest trim work, the truck looked nearly stock. Until it was in motion that is. No sport/utility on the planet moved like this truck. And even with 225 horsepower under the Mustang’s hood, this darn sport/utility was awfully tough to keep up with. Especially coming away from a tight turn , where the Jimmy seemed to just hook up lo the pavement and walk away from the Ford. No wheel spin , no bellowing engine, no drama- j ust an accele rationinduced vanishing act that had the Mustang’s occupants very confused and more than a little annoyed.
Such is life for unsuspecting drive rs who tangle with GMC’s latest stealth road rocket, the Typhoon. With 14 pounds of boost from a Mitsubishi turbocharger. all-wheel-drive designed specifically (or the street, four-wheel antilock brakes and a healthy dose of suspension tweaks, the Jimmy has been successfully transformed from an all-purpose family hauler to a screaming, four-alarm GT.
The first clue as to the Typhoon’s Doctor Jekyll and Mr. Hyde conversion is apparent when you climb aboard. Nearly everything inside is dressed in dark charcoal leather, with cushy cowhides covering the front and rear seats, the do o r inserts a nd the rear quarter panels. Even the interior spare tire cover is made of matching leather. You won’t mistake the front buckets for high-tech, multi-adjustable sport seats. but they’re sufficiently comfortable, equipped with inflatable lumbar supports and plenty supportive. Directly in front of the drive r is a plump, leather-covered four-spoke steering wheel that’s fitting for a truck with sports car intentions.
Beyond the steering wheel is an instrument panel that ‘s considerably better than the one it replaces. Gone is the awkward bar graph speedometer and gauge layout that plagued earlier S-10 Blazer and S-15 Jimmy dashboards. In its place is a collection of small but clear analog gauges with readouts for engine speed, coolant temperature, oil pressure, turbo boost and fuel level. All the information a driver needs is available at a glance.
Yet from the driver ‘s seat there’s still no denying that the Typhoon is based on a truck, and no amount of power accessories, fancy upholstery and upgraded sound systems is going to erase that impression. Until you turn the ignition key, that is. Because even though the 4 .3- liter V-6 is closely related to the Jimmy and S-10 Blazer powerplants, the Typhoon’s engine speaks an entirely different language than its domesticated cousins. The stock V-6 has its central throttle-body feeding system tossed out in favor of a far more precise and immediate port fuel injection design, the pistons and head gaskets are beefed up to withstand the rigors of turbocharged duty and a more substantial radiator keeps the whole operation cool and composed.
And about that turbocharger. Sitting below the right bank of cylinders, the blower turns compressed atmosphere and premium unleaded into 280 horsepower at 4400 rpm and 350 lb-ft of torque when the tach says 3600. A stock 4.3 V-6 makes 160 horsepower and 230 lb- ft of torque by comparison- which are very healthy sums to begin with. When the turbo hits 14 psi, an electronically controlled wastegate bleeds off destructive force, and an air-to-water intercooler stands between the turbine and the intake manifold to make the combustion process quite a bit friendlier for the pistons and spark plugs.
Start the engine and you still may not be convinced that there’s anything unusual going on under the blocky hood. At idle there’s little to distinguish this engine from its kinder, gentler kin. Only a slightly deeper exhaust note sounds a warning. Blip the accelerator and the rumble deepens and the 90- degree V-6 booms with the promise of massive torque.
Yank back on the floor-mounted shifter and a substantially modified Hydramatic four-speed automatic connects with a Borg-Warner transfer case and viscous coupler to tie both axles together. A limited -slip differential also lives between the rear wheels for even more traction. The liquid coupling between the front and rear axles sends 35 percent of the engine’s power forward to the steering wheels, and 65 percent to the back. The idea here is to make acceleration, not tire smoke.
Push the accelerator south and the engine’s low 8.3:1 compression ratio, turbo lag and the driveline’s weight and friction result in a casual launch. For the first 15 feet, that is. Then the tach passes 2500 rpm and everything changes, with the turbo blowing, the fuel injectors blasting and all 262 cubic inches making horsepower and torque like there’s no tomorrow. By 3500 rpm, the Typhoon’s soft springs have allowed much of the truck’s weight to pitch rearward and you’re catapulting toward Second gear in a violent rush.
The engine’s rev limiter abruptly steps in at 4700 rpm, but the automatic knows there’s no use in holding on past 4500 because the pushrod V-6 goes breathless soon afterwards. Second gear then happens so fast and so hard that the turbo never falls off boost and the sprint isn’t interrupted. Second gear stretches out longer than First, but the shift to Third is just as quick. The trans is calibrated for rapid-fire shifts, with only a slight softening as Fourth gear and the locking torque converter drift in at cruising speed under light throttle.
Even as the engine rips up and clown the rev range, only the hiss-whoosh, hiss-whoosh of the turbo boosting and the wastegate releasing pressure sounds unusual. Noise from under the hood is remarkably tame. Hold the Typhoon against its brakes and bring the engine up to 2000 rpm and the launch is anything but tame. Turbo lag evaporates, the driveline presses up against the fat tires and when you sidestep the brake and stomp the accelerator, the front wheels chirp and the truck fires forward with virtually no hesitation. The speedometer flashes past 60 mph in 6.5 seconds, and your back gets nailed into the seat.
Nearly 300 horsepower is substantial, but 360 lb-ft of torque is certainly enough to vaporize even the widest tire, so the Typhoon’s all-wheel-drive system is designed to send power to the wheels with the most grip, regardless of the situation. Even full throttle around a 90-degree turn results in nothing more than a bark from the inside front tire, as the rear differential distributes most of the engine’s torque between the two rear wheels. This rear power bias also reduces the tendency of all-wheel -drive street vehicles to understeer grossly when pushed. In all but the most demanding corners, the Typhoon retains a balanced, rear-drive attitude.
Clearly, the Typhoon accelerates like a sports car. But the thought of hustling 3800 pounds of truck around a corner at sports-car velocities might seem fool hardy at best. Even the greatest all-wheel- drive system in the world won’t keep a vehicle from falling off the road if there’s no suspension to back it up. So down it came, with the stock Jimmy’s tall, off-road stance swapped for a low, squat profile and a definite forward rake. Sway bars, bushings and shocks arc all pumped up for street battle, and the springs are softened for a more civilized ride and better compliance.
But the biggest contribution to handling is made by a set of extremely wide, extremely low-profile 245/50R16 V-rated tires mounted on 18×6-inch alloy wheels. The lowering helps, and the stout sway bars and bushings make a difference, but it’s the tires that really count. Head for a corner at speed, and the Typhoon’s body is tossed slightly to the side, the soft springs compress and take a set and the tires do the rest. In fast maneuvers, the steering is slow enough to keep from overpowering the suspension’s ability to control nearly two tons of girth. Eventually, a rhythm of toss and grip develops and the truck begins to feel nimble and easily controlled. The Typhoon is no Corvette in the twisties, but with some practice, it can dance with the best of them.
Should the exciting combination of horsepower, torque, traction and tires be too tempting, antilock braking control for all four wheels keep the Typhoon from spinning off into the weeds. Even with relatively old-fashioned rear drums, mashing the brake pedal never knocks the truck off balance. GM was wise to keep the steering slow and the brakes strong in a truck with this much punch.
For all of its technological tricks, the Typhoon is anything but a homogenized GT. The high-tech advantages of turbocharging, port fuel injection, all-wheel-drive and antilock brakes are mixed in with a truckish profile, a castiron pushrod V-6, a solid rear axle and fat tires. The result is a mighty entertaining sport truck. The turbo kicks, the tires bite and the Typhoon gets ballistic in a hurry. Toss in every convenience item from a CD player and cruise control to remote keyless entry and self-leveling rear suspension, and you have a matchless combination of sport and utility. It’s a $30,000 hot rod with a split personality.
