2004 Chevy Silverado - Superb Supercharged Silverado
THR's Screamin' Chevy
It's a big, red, rumbling rubber-burning, hot-rod pickup. What's not to like? It's truly amazing how THR-supercharged Silverados can effortlessly smoke the tires, even with their locking differentials and 20-inch Goodyears.
GM killed the Camaro at the end of 2002, leaving THR with nothing to build, so Henry began looking for alternatives. Wanting something affordable with a V-8 rear drive, the obvious choice was the Silverado. He and the techs at his dealership began developing the THR-supercharged Silverado for introduction in 2004.
Tom Henry owns a Chevrolet dealership in Bakerstown, Pennsylvania, about 15 miles north of Pittsburgh. The business was originally started by his father in 1958, and Tom, an avid hot rodder, later took it over. In the late-'90s, Tom Henry Chevrolet's involvement in motorsports spurred Tom to form a subsidiary, Tom Henry Racing (THR), to modify street-driven Chevrolets for higher performance, then sell them through his dealership. Fifty trucks were built between 2001 and 2002. Each had a LS1 V-8 engine and was performance-enhanced with aftermarket parts to either an 350 hp (automatic) or 380 hp (manual).
At the moment, Tom Henry Racing is not only selling its own modified Silverado, but it's also a dealer for Joe Gibbs Performance trucks. This gives THR not one but two very distinct tuner truck products: one for the street rod and drag racer types, and another for NASCAR-inspired truck fans. Because of this, he has earned his business' nickname of the hot-rod truck headquarters.
Enter the Supercharged SilveradoTom Henry Racing is putting an emphasis on performance and value, and the starting point is a 1/2-ton standard cab shortbed Chevy with either the 4.8L manual or 5.3L automatic powertrain and a 3.73 locking rear axle. Some of the convenience items THR orders are power windows and mirrors, tinted glass, and a tonneau. High-dollar stuff, such as extended cabs, all-wheel drive, Quadrasteer, leather seats, off-road suspension, OnStar, and so forth, are options.
While centrifugal superchargers are common for passenger cars in lightweight, high-performance street or drag race applications, a Roots-type supercharger is better for a near-5,000-pound truck. To make pickups wicked-quick on the street, high torque across the rpm range is a necessity. For that, a Roots-type supercharger, which makes plenty of boost in the midrange and holds it to high rpm, is the right choice for this application. THR uses the Magnuson Products Radix supercharger. Its architecture was developed by the Eaton Corporation for use in factory applications and had to meet stringent reliability and durability standards. Also, Magnuson offers a 3-year/36,000-mile limited warranty on powertrains equipped with its superchargers when they are installed by ASE-certified technicians, such as those at Tom Henry Chevrolet. The only changes to either engine in a THR Silverado are the supercharger package and a THR/Stainless Works low-restriction exhaust. According to Magnuson Products' dynamometer, the 4.8L manual makes 373 SAE-corrected horsepower at the rear wheels, and the 5.3L automatic puts out 387. Also, figure in 18 percent parasitic loss through a manual drivetrain and 22 percent through an automatic. At the crankshaft, those engines are making about 455 and 500 hp, respectively. The torque is 470 and 545 lb-ft.
Driving a Pair of 450hp TrucksWe enjoyed the 4.8L THR Silverado because its manual transmission was fun to drive. Even though it was 40 to 50 hp short of the 5.3L with the five-speed's extra gear, if the truck gets launched right and the tires hook, the stick and the automatic might be pretty close in the quarter-mile.
Not all aftermarket-supercharged engines demonstrate good driveability, but this one feels like it's well-calibrated, and its injector sizing and fuel pressure are well-matched to the blower. As a result, the truck's around-town driveability was about as refined as that of a stock Chevy pickup. The Radix has a bypass valve that allows airflow to bypass the supercharger when no boost is being produced, further improving light-throttle driveability and increasing off-boost fuel economy. When you run the truck hard, because a Roots-type blower makes a lot of boost down low, they respond quickly and go like no tomorrow. There's no inconsistency in the power delivery. Whether it's part throttle or wide-open, Magnuson seems to have done its calibration homework with the Superchips computer.
If you pop the hood, you'll see the appearance and packaging of the Magnuson blower has been nicely installed by the technicians at Tom Henry Chevrolet. The only problem we had with the 4.8L manual configuration was the stock Chevy shifter. Its lever is as long as a baseball bat; it has long throws and is hard to quickly shift. Hurst makes a shorter throw shifter for late-model GM trucks that should be part of this package.
The 4.8L is a blast, however, if you want maximum quickness, you have to drive the blown Vortec 5300 because of its 500 hp and four-speed automatic. Drag racers will have an easier time with the automatic. In addition, many truck buyers want its convenience.
The down side to the 5300 THR Silverado is if you think the 4.8L five-speed burns rubber, the bigger motor positively nukes the tires. It's better to have 20s, two sets at a time.
A THR Silverado's suspension and steering is appropriate for everyday street use. Four-wheel disc brakes combined with GM's dynamic rear proportioning system performs well. The truck uses ride height sensing and the ABS computer to modulate rear brake pressure in maximum braking situations when the truck is lightly loaded. If the stock brakes are not enough, THR has a Baer Brake upgrade available.
Those who want better handling may wish THR had a performance suspension setup. The problem begins when you try to lower the truck and still use 20s. To satisfy the boy-racer set, THR needs a package of lower ride height, aftermarket springs, stabilizer bars and shocks, and 18-inch radials, such as the Goodyear F1 Supercar. You'd be trading image for performance, but if you want to rip around corners quickly, you need stiffer springs, bars and shocks, and shorter, stickier tires.
We can all be seduced by the exhaust rumble of a V-8 hot rod. Tom Henry Racing partnered with Stainless Works, an Ohio manufacturer of performance exhaust systems, to develop a low-restriction exhaust for the Silverados. Not only does it provide the lower restriction needed by the blower motor, but at some engine speeds, its sound is a throwback to the musclecar era because its chambered mufflers are similar to those on late-'60s and early '70 Chevys. Its throaty, low-rpm rumble becomes a V-8 howl. If you add the supercharger noise at high boost, you have a truck that sounds as fast as it feels.
As for color, you can have anything that the THR-supercharged Silverado Chevy offers. Regardless of color, you'll get the THR treatment, including 20-inch Goodyears on American Racing Torq-Thrusts, a stainless-steel exhaust with polished dual, outlets, a tonneau, a tailgate spoiler, and a color-keyed front bumper. THR interiors are nice and clean but not too fancy. For upholstery, THR takes the stock seats, re-covers them with hound's-tooth inserts, and adds custom headrests. Also, THR replaces the stock gauges with a setup from a Cadillac Escalade.
How quick is one of these blown Silverados? The two we drove were brand-new units, both for sale on Henry's lot. One had 31 miles on it and the other had 73. Since neither was broken in, we didn't go to the dragstrip. With that said, and looking at their weight, 4,735 pounds, as well as Magnuson's claims of performance from its blowers, we think the THR-supercharged Silverado with the 4.8L - the blower making 7-psi boost and the driver doing the right stuff on the starting line - ought to run the quarter-mile in the high-13s or low-14s at around 100 mph. The 5.3L automatic will be a little bit quicker. Either way, whether you choose the 455hp 4.8L or 500hp 5.3L, a THR-supercharged Silverado rates pretty high on our fun-to-drive list.
As for a place to start, THR is better than most, increasing performance where it counts, without lowering driveability. For better performance, contact: Tom Henry Racing, Dept. TR, 5886 Rt. 8, Bakerstown, PA 15007, (887) 842 4389, firstname.lastname@example.org.