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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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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