The return of the ZR1 for 2009 heralded the revival of a fabled Corvette moniker. Like its C4 progenitor, the new Z boasts a unique engine and an emphasis on flat-out speed. But with its world-beating performance and aggressive appearance, this over-the-top C6 has arguably committed an act of lese majeste by stealing some of the grandeur from its older sibling.
Rather than brooding like a Danish prince, Corey Henderson's '91 Corvette ZR-1 has risen to the challenge posed by the new king. Henderson is the owner of Henderson Performance Technologies, a performance shop in New Braunfels, Texas, and he's recognized as something of a C4 ZR-1 guru. Using the resources at hand and a passion for Corvette performance, he built his ostensibly humble car to have the power of a vicious tyrant.
Owning a ZR-1 was a longtime ambition that Henderson assumed he would not fulfill. "I had always loved the ZR-1 as a kid but knew I would never be able to afford one," he says. As he grew financially sound with age, Henderson was able to realize his dream and purchase his '91 Z in 1997. "Of course, the realization at that point was that though I now had a ZR-1, I wouldn't be able to afford to modify it, as the cost was extremely prohibitive." But once again Henderson proved himself wrong, this time by augmenting the already-prodigious power of his mighty king.
Much like the contemporary LS9, the C4 ZR-1's Lotus-designed LT5 engine is a unique specimen among Corvette powerplants. The sophisticated motor features an all-aluminum build and a dual-overhead-camshaft valvetrain. While it was a low-production engine, many of its advances were carried over into the Northstar and LS1 mills. "All the LS-based engine owners out there should take a minute to say, 'Thank you, LT5,'" Henderson says with a smile. These motors are known for their naturally aspirated power potential, and Henderson's is no exception.
Henderson procured a '90 LT5 from a junkyard and set out to build it into a 368-cube screamer. "After about a year of collecting parts, I put her together and swapped out the engine," he says. A rotating assembly comprising the stock crank, Eagle rods, and JE forged pistons was used, bumping compression to a stratospheric 12.25:1. The original cylinder heads were ported and treated to Jeal EA22 cams on the intake side and exhaust cams from the 405hp '93-'95 LT5. The stock intake manifold and throttle body were then ported for improved breathing ability.
The motor exhales through a set of Geoff Jeal headers with outsized 2-inch primaries and 3-inch collectors. The car also features a B&B 3-inch dual exhaust system with a cross-pipe exhaust system. To maximize the benefit of the performance parts, Henderson tuned the car himself on his shop's in-house dyno.
After a nearly three-year build process, the ZR-1 was completed in 1999. The end result of Henderson's tinkering is an impressive 502 hp and 446 lb-ft torque at the wheels. This royal might propels the car through the quarter-mile in 11.42 seconds at 125.8 mph. But despite its imposing power and extensive modifications, Henderson's ZR-1 has been a paragon of reliability. "For the past 10 years, I've done nothing but change the oil and spark plugs in the car," he says. "You can't ask for much more than that."
It's worth noting that the ZR-1's impressive straight-line celerity does not come at the expense of handling. Wanting an all-around performer, Henderson improved the original suspension with DRM coilovers at all four corners. To harness the power increase, the factory stoppers were also enhanced with a Brembo big-brake kit in front and cross-drilled rear rotors. On the street, the car sports the original 17-inch A-mold wheels shod in BFGoodrich Comp T/A tires in the front and sticky Yokohama AO32Rs in the rear. For dragstrip outings, Henderson uses Mickey Thompson ET Street race tires on a separate set of wheels.
Even with the significant power increase, Henderson's Z still employs a stock clutch. The ZF six-speed transmission has received a Hurst short-throw shifter, and the Dana 44 rearend benefits from a set of shorter 3.90 gears.
While the C6 ZR1 flaunts its extreme performance with a chiseled body and exposed blower, the C4 iteration abjured such royal regalia. This was especially true after the '90 model year, when the ZR-1's unique rear-fascia styling spread to all Corvette models. Among the few hints to the special nature of the fourth-gen Z were its tumid rear wheels, a handful of badges, and high-mount third brake light. Henderson has left the exterior in its factory form, largely to avoid involuntary contributions to his local government. "I have a hard enough time keeping the ticket writers out there from pulling me over as it is," he says. "If I had too much 'bling' on the car, I'd just be that much more of a target."
While Henderson performed the majority of the build himself, he credits the "local Texas Bunch"--Mark Randolf, Bob Hall, and Dewey Slocum--with helping to bring his ZR-1 to its current regal status. "Extra hands are hard to find sometimes," he says, "and without these guys around me, it would've been a much less enjoyable project." In a testament to the infectious nature of the Corvette hobby, Henderson's mother has her own Admiral Blue '95 ZR-1. "We're a ZR-1 family," he says. Henderson also owns an '87 Vette with a supercharged and nitrous-injected 383 stroker, which he describes as "a grocery getter-really."
C5 and C6 Corvettes are the mainstay of his shop, but Henderson's enthusiasm is focused squarely on the old-school ZR-1. He does, however, admit that parts availability poses a significant challenge in keeping C4 Zs on the road. "GM really dropped the ball in supporting these cars after they made the decision to pull the plug on the LT5 in 1993," he says. "I've spent the last 10 years accumulating many of the service items required to keep the LT5 healthy and happy, but when my supply is depleted, it's anyone's guess what will be available from the aftermarket suppliers." While Corvettes are his passion, Henderson also works on various domestics and imports. He's not afraid of a challenge, having built an LS1-powered BMW 3-series and installed a fully built, turbocharged LS2 in a Fox-body Mustang.
Corey Henderson's '91 ZR-1 is the realization of a dream, and the car has been accorded an appropriate level of enthusiasm. The build process has been carried out with an air of noblesse oblige to maintain the relevance of a truly special Corvette. Rather than being rendered obsolete by a lack of high-tech gadgetry, it stands proudly as the once and future King of the Hill.