C6 Corvette ZR1 Convertibles - Drop-Top Guns

A pair of convertible fanatics build their own topless ZR1s. Will GM follow suit?

Randall D. Allen Mar 31, 2011 0 Comment(s)
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"Hey, Dad, is that a Corvette with a roof?" asked a 10-year-old Ray Craig Jr. during a father-son drive that took place long ago. "It sure is, Son," answered Ray Craig Sr., spotting the hardtop in question, "but there's nothing better than a convertible Corvette like the '64 you're riding in now."

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Ray Sr. still has that '64 convertible, and as it nears its 46th year with its original owner, one has to wonder if it (and the '60 'vert he purchased as his second collectible Vette) didn't make an indelible impression on his son.

"Growing up in Oklahoma, Dad always had convertible Corvettes, so whether I was born into a love of sports cars or simply picked up his weakness for them is a point of debate," says Craig the younger. "As my computer business grew, and Dad retired from being a school superintendent, he joined me in the business and our mutual Vette hobby grew."

Father and son purchased '99 and '01 convertibles and soon started modifying them for more power. While Ray Jr.'s car received a built, LS1-based 383 that put out 570 hp, Dad waited a bit longer and stabbed a 608hp variant into his drop-top. The year 2006 proved to be a pivotal one for the two, as they traveled to the Eureka Springs Corvette Weekend in their C5s and got a first glimpse of the new Z06. After spending most of the day looking over the Z, Ray Jr. turned to his father and said, "I sure would like to have one of those, but there's a problem: They aren't offered as convertibles."

And so, after a short time pondering the possibilities, the pair decided to build their own. Not only did they pull off that incredible feat, but when the ZR1 was released in the summer of 2008, they set out to create the ultimate Corvette head turners: convertible ZR1s.

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According to Ray Sr., the first question most people ask about the cars is whether they started out as fixed-roof Vettes or convertibles. "When we first started looking into how to create a [Z06] convertible, I spoke with a chassis engineer at GM, who gave me two key pointers: Don't cut the top on a fixed-roof design such as the Z06, as the strength and chassis rigidity are in the top. Instead, integrate the unique components, such as the wider rear quarters and carbon-fiber body panels, onto a base convertible."

Working in conjunction with Parham's Body Shop in Chickasha, Oklahoma, the pair undertook a process of grafting together Z06 lower and convertible-specific upper rear quarter-panels. Incredibly, the cars retain not only the full function of the power top, but also their original fuel-filler doors.

To begin the ZR1 builds, both Craigs ordered convertibles in 3LT configurations. In addition to the base LS3 engine and six-speed transmissions, they wanted to selectively equip the cars to ensure that they were as close as possible to a factory-ordered ZR1. Grady White of Knippelmier Chevrolet in Blanchard, Oklahoma, helped them navigate through the options to select the all-important Magnetic Selective Ride Control and AM/FM seven-speaker Bose sound system.

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Ray Jr. chose a Black exterior (code 41U), while Ray Sr. selected Machine Silver Metallic (code 67U). Both cars were ordered with Titanium interiors and Ebony convertible tops. Ray Jr.'s car arrived first as a late-'07 model, and Ray Sr.'s car arrived shortly thereafter as one of the first delivered '08 convertibles.

Next, the Craigs focused on the daunting task of acquiring all of the ZR1-specific body panels, along with the LS9 engines and related hardware. Don Kauffman of Knippelmier Chevrolet was instrumental in tracking down the body parts, while the conversion from LS3 to LS9 was expertly handled by 21st Century Muscle Cars in Addison, Texas, with assistance from Lingenfelter Performance Engineering (LPE).

While you might assume that the majority of parts could be obtained through GM's computerized parts system, the Craigs' experience proved otherwise. According to Ray Jr., "When we started converting the cars, the ZR1 had only been recently released. In addition to not having part numbers assigned, there was no such thing as a ZR1 crate engine. Kerri Lingenfelter Page of 21st Century spent countless hours working with the people at LPE back in Indiana [where she had previously worked for her late father, John] and GM to procure the hundreds of ZR1- and LS9-specific parts."

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Since LPE and GM work closely on many projects, the Craigs were able to purchase LS9 crate engines and engine controllers well before the decision was made to offer them to the public. Other items were more difficult to track down. GM designed hundreds of ZR1-specific components, including the alternator bracket, alternator, air-conditioning bracket, and compressor, all of which differ from their LS3 counterparts.

Unlike the Z06 conversions, the biggest challenges of this job were not body related. After Mike Parham made quick work of integrating the ZR1 bodywork, the conversions hinged on the team's ability to determine the differences between the stock and ZR1 parts, and integrate them. For the engine, drivetrain, suspension, wheels, and everything in between, the process consumed a solid eight months.

"While the LS9 engine, engine harness, and controller were very difficult to obtain, the small stuff like the heat-exchanger pumps and tanks, along with all of the ZR1 connectors, hoses, and suspension components, offered up tremendous challenges," says Page.

The Craigs knew from the outset that the power of a stock ZR1 would never satisfy their need for performance. As both 21st Century and LPE were developing power packages for the ZR1, the teams worked together to pump up the LS9s to nearly 800 horses, all without hurting driveability or diving into the bottom end of the engine. In this case the first step was a 21st Century 21CMC-30 cam, which was developed to take advantage of the LS9's desire for larger exhaust durations.

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According to 21st Century's John Page, "In changing the stock ZR1 upper pulley and harmonic balancer over to the LPE units to raise the boost levels to 14 psi, we had to address two key elements: controlling the increased heat from the supercharger and evacuating the exhaust. The custom-designed front-mount Spearco intercooler provided the foundation for controlling the heat, while the headers and exhaust allowed the camshaft to pull in more intake air and expel it efficiently." When testing was finally completed, the cars were able to put out an estimated 770 hp and 780 lb-ft of torque (at the crank) on a very safe tune.

According to Ray Jr., "Driving the ZR1 convertibles is hard to put into words. Combine the open-air element of a C6 convertible with the spine-twisting power of a tweaked LS9, and you're at the edge of sensory overload. My dad and I share so many passions, and one of them is driving the cars to Corvette events all across the country."

Ray Sr. continues, "It's funny that the older we've gotten, the closer our families have grown. A common bond of Corvettes was the key, which all started when he was in elementary school and begged to cruise with me in the '64. Combined, we own nine Corvettes. They're all convertibles and have come to mean two things: fun and family. Will there be another new Corvette convertible project? You bet. The exterior colors may differ, but under the skin they'll share the same DNA."

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