As Chevy and GMC generated big bucks selling SUVs in the late '80s, Buick engineers lamented the demise of their highly developed, outrageously quick turbocharged 3.8-liter V-6. To keep themselves amused, they would stick 3.8 Turbos in every Buick that would accept one and rattle around the proving grounds. Reattas! Electra wagons! When Buick ran out of its own turbo-compatible cars to Frankenstein, the automaker played around with other GM platforms. The 1989 Pontiac Trans Am Indy Pace Car was a direct result of this engineering gallimaufry. And so was the GMC Syclone, which started as the Buick guys' hot little shop rocket, featuring a Grand National engine living under the hood of a Chevy S-10 pickup.
Buick pitched its blown S-10 idea to Chevy, who rejected it since they had the 454 SS on the boil, so they pitched it to GMC. GM's all-truck division had long ago been paired with Pontiac in GM's corporate marketing machinations. Perhaps seeing the flood of great press that the 1989 Turbo Trans Am brought to its corporate sibling, GMC got on board with converting its S-15/ Sonoma compact pickup—but the division required a few tweaks to Buick's formula to ease production.
Not least of these was adapting Buick's turbo expertise to the GMC's 4.3-liter LB4 V-6, since the S-15 would need considerable engineering work to make the Buick 3.8 fit. The Typhoon's basic engine was GM's all-iron LB4 V-6—three-quarters of a small-block Chevy V-8, which became the base six-cylinder engine in multiple car and truck lines starting in the 1980s. It shared the 350's bore and stroke, although the crank had 30-degree offsets between rod pins in order to make a proper even-fire engine. The 1.94/1.60-inch valves were also shared with the small-block. In the early '90s, with a 9.4:1 compression ratio, the LB4 was good for 160 horsepower.
That was just the starting point. Using electronic multi-point fuel injection (including Corvette-spec fuel injectors), a single Mitsubishi turbocharger pumping out an electronically regulated 14 psi of boost, and a Garrett water-to-air intercooler, GMC found 280 hp and a whopping 360 lb-ft of torque. In an era when most hot cars were approaching 300 hp, a 280-hp truck was an eye-opener. (Stock versions have long been rumored to have more chutzpah than a lighter 300-hp Corvette, with the power rating downplayed to keep the Bowling Green bosses quiet.) Other changes included a compression ratio drop to 8.35:1, a specific intake manifold that integrated the TPI-injected Corvette's twin-throat 48-mm throttle body, nodular iron main bearing caps, graphite-composite head gaskets, and more.
The only available transmission was a 4L60 four-speed automatic, which was also cribbed from the Corvette. The all-wheel-drive system, borrowed from the Chevy Astro/ GMC Safari vans, split torque automatically through the transfer case, with one-third to the front wheels and two-thirds headed out back; a viscous coupling (incorporating silicone fluid and no less than 51 clutch plates) sensed which wheels were slipping in sloppy or extreme conditions, and reassessed power distribution accordingly.
Suspension was slammed and stiffened— the gently raked pickup sat nearly 3 inches closer to the ground than a standard-issue Sonoma—and the power headed out to four 16 x 8 cast-aluminum wheels wearing 245/50VR16 Firestone Firehawk rubber. Brakes were 11.9-inch rotors in front and 11.2-inch drums in back, with full antilock capability. Lower body cladding (incorporating fender flares, a front spoiler with fog lamps, and a rear roll pan—a body kit so brutal they didn't even bother to paint it) helped give shape and nuance to the aging design.
Inside, the cabin was chock-full of toys: bucket seats, leather-wrapped four-spoke steering wheel, power locks and windows, air conditioning, cup holders, and more. A Pontiac Sunbird GT Turbo donated its gauge cluster. It incorporated three main gauges: a 120-mph speedometer front and center, a combination tach and boost gauge on the right, and a quartet of sweep needles in the nacelle on the left, which told fuel level, oil pressure, water temp, and battery charge.
The exterior registered as sinister. Add gallons of black paint and some snazzy sticker-badging, and voila! When it arrived for the 1991 model year, GMC called it Syclone; Ford still owned rights to the Cyclone-with-a-C name, and in fact had used it on a show car just a year before. It was an instant legend. Just 2,998 were built; Syclone was a 1991-only proposition.
In 1992, Philip Morris gave away 10 specially modified Syclones: American Sunroof Corporation made the roof a fully removable targa panel, Goodyear Eagle GS-C tires rolled on Boyd Coddington billet wheels, and each was painted a PPG-supplied shade of red that looked an awful lot like Marlboro cigarette red. Borla exhaust, a Belltech lowering suspension kit, Momo steering wheel, leather Recaro seats, and a Sony stereo were among the additions.
SPECIFICATIONS
Engine OHV V-6; iron block and heads, turbocharged
Displacement 262-cu.in.
Horsepower 280 @ 4,400 rpm
Fuel system GM electronic engine-control system with port fuel injection, Mitsubishi turbocharger
Transmission GM 4L60 four-speed automatic with lockup torque converter
Wheelbase 108.3 in
Overall length 180.5 in
Overall width 64.8 in
Overall height 60.0 in
Shipping weight 3,600 lbs
One of the ultimate C5 Z06s was the 2004 24 Hours of Le Mans Commemorative Edition, acknowledging Corvette Racing’s historic 1-2 class finishes in 2001 and 2002 (also 2004). Just 2,025 Le Mans Commemorative Editions were built assuring their collectability.
As far as the regular Z06 goes, all told, there were 28,388 built over four model years, so they’re not difficult to find these days. It can, however, be difficult to find stock, low-mileage examples, as many owners drove these cars as they were intended and tweaked them with bolt-ons for even better performance.
According to classic.com, average C5 Z06 prices have increased significantly over the last five years from $16,000 in 2019 to $32,000, as of this writing. One of the highest prices recorded for an unmodified example was at Mecum’s Kissimmee sale in January. The car was a 2001 painted Speedway White (one of 352 in that color) with just 218 original miles, and it sold for $71,500 including fees.
In July 2023, a black 2004 Z06, driven fewer than 1,600 miles, sold on Hemmings Auctions for $52,500 - just shy of the car’s original MSRP of $53,485. On the more affordable end, back in 2020, a 2001 Z06 listed as unmodified, but with 154,680 miles on the odometer, changed hands on Hemmings Auctions for $9,000.
These cars have received a lot of attention lately and appeared on many bargain-priced performance car listicles. Their low-buck status seems to have changed as a result and prices have nosed skyward. Still, the first-edition Z06 is an excellent car that offers a lot of track day potential with very low running and maintenance costs. If you’re interested in owning a 2001-’04 Corvette Z06, here are some points to consider.
Body
Image: General Motors Artist: David Kimble
C5 Corvettes used sheet-molded composite body panels made of 40 percent resin, 33 percent calcium-carbonate filler, 20 percent chopped fiberglass, and 7 percent resin and hardeners (used to improve the surface finish of the panels), according to Chevrolet. The floor pan was made from SMC inner and outer panels with balsa wood sandwiched in between. The 2004 Le Mans Commemorative Edition Z06 used a carbon fiber hood to shave 10 pounds off the nose. When inspecting a Z06, you’ll want to inspect the lower portions of the car for signs of damage—the fascias and rocker panels. The three-piece air dam on the front is prone to taking hits because it rides so close to the ground. Replacement air dams are widely available and it’s important that the pieces be installed correctly as the dam helps direct air to the car’s radiator. You will also want to check the floorpan for signs of damage or previous repairs. Floor pans punctured by debris in the road aren’t unheard of on these cars and you’ll want to make sure the repair was performed correctly to guard against leaks. The quarter panels on these cars are bolted on, so check for proper fit and signs of replacement that might indicate previous accident damage. Aftermarket body kits are available for C5s and popular with Z06 owners looking for some additional body width and larger wheelhouse openings.
Something else to be aware of - common among all Corvettes, not just C5s - are electrical grounding issues related to the composite body. These can cause a wide variety of mysterious conditions and usually the problem isn’t difficult to solve but can be difficult to trace.
Z06 exterior colors over the C5 generation included: Black, Torch Red and Millennium Yellow from 2001-’04; Speedway White, which was only available in 2001; Quicksilver, which was offered from 2001-’03 and replaced by Machine Silver in ’04; Electron Blue, which was offered in 2002-’03; and LeMans Blue Metallic was used on the ’04 Le Mans edition Z06. All of the LeMans editions were painted blue with silver and red graphics modeled after the 2003 C5R race car.
Chassis and Suspension
Among the most scarce of all C5 Z06s is 2004 24 Hours of Le Mans Commemorative Edition acknowledging Corvette Racing’s historic 1-2 class finishes in 2001 and 2002 (also 2004). Just 2,025 Le Mans Commemorative Editions were built, and they command a premium today. All of the LeMans Commemorative Editions were painted blue with silver and red graphics - a color scheme modeled after the 2003 C5R race car.
Photo: General Motors
The C5 Z06 was based on a pair of 13-foot long, continuous chassis rails, hydroformed in a die using fluid pressure - it was a very rigid platform and a first for the Corvette. Another substantial change in the C5 chassis, that made it an ideal production road racer, was the use of a rear transaxle. By moving the gearbox to the rear, the weight distribution nearly hit the 50/50 sweet spot, plus it freed up space in the cabin. An enclosed stamped-steel driveshaft tunnel (a torque tube) between the engine and the transaxle made the chassis even stiffer. The suspension hard parts were made from aluminum and transverse mounted leafs handled the bumps. The C5 front suspension used a setup similar to the late-edition C4s, with revisions, while the rear was an entirely new design with upper and lower A-arms and constant velocity joints replacing the old five-link/universal joint setup. Without a doubt, the C5 chassis transformed the Corvette. In addition to the superior handling, the cabin was easier to enter and exit, more comfortable to drive and the ride was less punishing—even the track-ready Z06. To ensure the Z06’s track readiness, it had unique FE4 suspension with a larger front stabilizer bar, a stiffer rear spring, revised camber settings and forged wheels that were 1-inch wider front and rear than a standard Corvette. The Z06’s steering was sped up too: 2.46 turns lock-to-lock versus 2.66 on standard C5s. Brakes were shared across the C5 line—four-wheel discs with 12.8-inch rotors front and 12-inch rear. The calipers were two-piston units but treated to a red finish on the Z06. Many owners choose to upgrade the stock brakes with aftermarket units. The stock rotors are fine for street use but have shown not to hold up well on cars that are driven hard on the track.
The 2004 model year Z06 benefitted from suspension revisions and new shock absorbers that were developed by GM through extensive testing. These units were a vast improvement over prior years. There are aftermarket options available that approach the performance of the factory ’04-edition shocks—which can be expensive and difficult to find today. Many owners have found that OEM C6 Z06 shocks are also a good fit at a lower price. The C5 chassis is a rugged and proven sports car platform that was designed to serve reliably for many miles. When shopping, take note of the typical items that wear out with age: anti-sway bar bushings/end links, control arm bushings, rear cradle bushings, ball joints etc. Be sure to ask about any maintenance work that might have been performed. A fresh set of tires is a selling point on these cars as well. The stock size Eagle F1 tires cost more than $400 apiece for the 265/40R17 fronts, and more than $600 apiece for the 295/35R18 rears - if you can find them. The selection of tires available in the factory sizes is limited these days so when it comes time for replacement you might have to consider alternatives like 255/40/17 or 275/40/17 fronts and 285/35/18 rears.
Engine
Image: General Motors Artist: David Kimble
The 5.7-liter LS6 arrived in 2001 with 385 horsepower and made the jump to 405 horsepower in 2002. It was an evolution of the standard Corvette’s LS1 with improvements to the block and pistons, better flowing heads with revised combustion chambers, a more aggressive camshaft, a redesigned intake and more. The LS6 is an excellent and proven performance engine that will serve many thousands of trouble-free miles. Initially, excessive oil consumption was an issue, but the problem was addressed in a Technical Service Bulletin. Replacement piston rings (due to a sealing issue) and a replacement engine valley cover (due to leaking) were prescribed for circa-2001 engines affected, and the changes were made in production to later LS6s. Reports and discussions of valve spring failures on 2002-’03 engines in particular also abound on internet forums. Replacing valve springs is a relatively cheap and inexpensive upgrade and is worth considering if the seller hasn’t performed the work already. Some of these engines have also suffered from separated harmonic balancers and balancer bolts that loosen and allow the balancer to come off - check for a wobbling lower engine pulley when the engine is running. The factory balancer is a press-on fit but there are aftermarket versions available that can be pinned to the crankshaft. Upgraded balancer bolts are also available.
Transmission and Axle
The Z06’s instrument cluster bears the logo of the popular performance package, and the tach has a 6,500 rpm redline.
Photo: General Motors
The Z06 used the TREMEC T-56 gearbox but it was equipped with more aggressive gear ratios for harder acceleration than the base Corvette. The trans was rear-mounted to a Getrag differential shared with all C5 Corvettes. Z06s were equipped with a 3.42:1 gear set with shot-peened ring and pinions.
The T-56 is an excellent gearbox, but miles and abuse can take a toll leading to some of the typical manual transmission maladies: grinding between gears, sticking in gear, popping out of gear etc. Sometimes the issue can be as simple as the shifter or the mount being loose, but some of these symptoms could also be signs of worn synchros or a damaged shift fork. The good news is parts are widely available and finding a knowledgeable rebuilder isn’t difficult.
The C5’s Getrag differential is a bulletproof and reliable unit that can withstand plenty of driving and punishment. The biggest issue with these has been seal leaks—something that was addressed in a circa-2003 technical service bulletin covering all C5 Corvettes. The TSB recommended replacement of the output shaft seal and the differential side cover O-ring. If a Z06 you’re looking at hasn’t had the work done and appears to be leaking, those seals are likely the culprit—and most frequently it's the output shaft seal. (Some techs recommend not disturbing the side cover if it isn’t leaking.)
Some C5 owners have also experienced issues with the clutch pedal sticking in the down position or returning slowly. Sometimes this can be solved by flushing and replacing the fluid in the hydraulic system. There are also aftermarket clutch return spring kits that can deliver more positive pedal action - once the fluid has been replaced and the system bled (an important maintenance item).
Interior
Z06 interiors were black or black with red accents and embroidered headrests. The Le Mans Commemorative Edition (shown) had graphite-colored upholstery with the Corvette emblem in the headrests instead of the Z06 logo.
Photo: General Motors
C5 Z06s had a unique instrument cluster with a Z06 callout on the tachometer and a 6,500 redline indicated. The bucket seats had additional side bolstering and embroidered Z06 logos on the headrests. Colors were limited to black, black and red and there was a graphite-colored interior for commemorative-edition ’04s with the Corvette crossed-flags emblems stitched into the headrests. It’s common to see worn leather side bolsters and seating surfaces in these cars but there are aftermarket covers and kits available to update shabby looking buckets. Many owners have complained of wind noise in C5s as the window seals age. Water leaks around the weather stripping is also a common problem. A locked steering wheel that can’t be unlocked, accompanied by the “Service Steering Column” message on the driver information display was one of the most common C5 interior issues reported. A 2004 recall addressed the issue (the recall number was 04006) and any car you’re considering should have had the recall work performed. Some owners took matters into their own hands and installed an aftermarket bypass kit that allowed the lock to function without interference from the car’s body control module. These seem to solve the problem as well.
Parts Prices
The Z06’s LS6 V-8 is generally a dependable engine. Horsepower was rated at 385 in 2001 and 405 from 2002-’04. Broken valve springs are a known issue, particularly on some 2002-’03 engines.
Photo: General Motors
- Air dam $114
- Brake rotor $60
- Carpet kit $680
- Harmonic balancer (aftermarket) $340
- Harmonic balancer bolt $41
- Seat covers $1,400
- Tires (front) $453
- Tires (front) $620
- Valve spring kit $100
What To Pay
Add $1,000-$2,000 for 2004 Le Mans Commemorative Edition
Did we leave out your favorite? If so, let us know in the comments. And if you're interested in reading more about classic American luxury cars, keep a lookout for the special feature in the July issue of Hemmings Motor News.
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