It was a car that could do over 220 miles an hour on the back stretch at Daytona, then drift through the high-banked turns like a World of Outlaws car, fully under control. The "Spirit of Sebring" Corvettes built by John Greenwood in the mid-'70s represented a high water mark in the design and construction of road-racing Corvettes. These were the last cars that he built using the production C3 Corvette frame; his later cars were full-tube-chassis ones.

It was, in Greenwood's words, the wildest production-based road racer to date, much less the wildest production-based one ever. "Without a doubt, the #75 car was, for me, the most fun, biggest rush, and biggest reward for doing all that kind of stuff, of any car that we ever did," Greenwood says from his Apopka, Florida Corvette store, Greenwood Corvettes. "That was THE car...that car was a bad boy!"

Back in the spring of 1975, we saw the #75 "Spirit of Sebring" Vette in action at Laguna Seca, in an IMSA Camel GT Challenge race. As Greenwood recalls, that race was as much a test/research-and-development session as it was a competition against the factory Porsches and BMWs in the field. "We didn't do well there," he says. "There was a learning curve with the car." Once he took the fast line on that curve, Greenwood wound up with a car that ran up front in both IMSA Camel GT and Trans Am-and scored three wins in Trans Am, leading to that series' 1975 championship.

Greenwood's foray into road racing followed a successful career street-racing W-engined Chevys (Impalas and Corvettes) on Woodward Avenue outside Detroit. Turning to road racing in the late '60s, after initial success at the club level starting at Waterford Hills, Greenwood took his Corvette racing operation nationwide, winning two consecutive Sports Car Club of America (SCCA) A/Production National Championships in 1970-71.

A sponsorship deal with BFGoodrich in '72 resulted in his first highly-modified Vette racers, called the "swing-arm cars" by Greenwood, which he ran in IMSA's Camel GT Challenge and SCCA's Trans-Am Series in 1972 and '73 (scoring three Trans-Am wins in '73) wearing ZL1 flares over their shaved BFG Radial T/As. His next race cars after the swing-arm cars, were to be progressions, while still wearing BFG's regular-production tires.

Troubles with Goodrich's production-derived tires--when they switched from 60-series to 50-series ones to race on in '73--led to on-track problems, and the BFG program ended after that season. But that didn't stop Greenwood from getting design, fabrication and technical help for his next C3 race cars.

It started at a test session on the big oval at central Ohio's Transportation Research Center (TRC). "At the time, I was getting more and more associated with Zora Arkus-Duntov," Greenwood recalls. "He and I sat down and talked, and I said, 'I want to build the most highly-modified platform car.'" Nothing brought out the best in Zora like a challenge-especially one involving Corvettes, as Greenwood witnessed. "As I'm sitting there talking to Zora, we're sitting on a curb and I'm telling him what I'm doing, and he's talking about the body work, and he wanted to make this wide body with the fender flares angling up. He just kept going with his hands, and explains to me how he wanted to make the fenders and bodywork on the car." And, so was born the concept of using wider bodywork to create downforce.

Greenwood's new racing Corvette turned out to have as much state-of-the-art Chevy and GM help as a privateer could dream of back then, as GM's corporate racing ban didn't end for another decade. "We came up with a deal where they ended up designing the body that was on the car at GM, at Chevrolet's Advanced Styling studio," says Greenwood, who also notes the contribution that future-GM Styling boss Jerry Palmer (and its then-current chief, Bill Mitchell) made at the time, as well as Randy Wittine's. "They made some temporary 'tools' (body tooling), and gave me the first tools. We made a deal where we would go ahead and produce the parts, for any Corvette person who wanted to use them. The parts ended up being homologated for FIA, so we could run them at LeMans (or in any other FIA-sanctioned races). [Zora] ended up having the clay model done, and they made the parts." Also, those wide-body parts got GM factory part numbers, and were listed in the Chevrolet Power service manual (along with stuff like LS7 crate engines and bare ZL1 blocks) for Chevy racers that was released in the mid-'70s.