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Here's the story:
lllustrated Corvette Series No. 148 - 'Zora Arkus-Duntov's Mule Corvettes - Pt. II"

Zora Arkus-Duntov was the perfect man for his time at GM. As his friend and coworker Gib Hufstader explained, “Zora was always anxious for more of everything.” Had Duntov come along 20 years later, it’s unlikely he could have gotten away with building the kinds of cars he did. But while only a small percentage of Corvettes ever get close to a race track, we all get to enjoy the fruits of Duntov’s automotive passions. Most of his test, or “mule,” Corvettes were never seen by the public, but those that were made long lasting impressions of what a Corvette could be.

The introduction of the L88 in ‘67 floored everyone. This was as close to an all-out, factory-built racing Corvette as the public would ever see. America had moved from the jet age to the space age, and race cars were using more and more exotic lightweight materials such as magnesium and aluminum. Duntov had been wanting an all-aluminum engine for the Corvette since 1956. (Engineers were even working on an all-magnesium engine for the car. Can you imagine how much that would have cost?) Bolt-on aluminum chassis and engine components were one thing, but an all-aluminum engine was another. The alloy-headed L88 was definitely a step in the right direction, but it would take 30 years for the all-aluminum LS1 to arrive.

When the automotive press arrived at the Milford test facility in the summer of 1968 to preview the ’69 models, they weren’t prepared for Duntov’s latest toy: the ZL1-powered Corvette. The only things missing from Zora’s white ZL1 car were sponsor graphics and numbers. The car had killer looks and grunt to match. The objective was simple: take one Corvette roadster, all the latest performance parts, and build it like a racer would. Everything that didn’t belong on a race car was removed. By the time they were done, Duntov and his crew had reduced the weight of the car by about 400 pounds, to approximately 2,965 pounds. The ZL1 engine alone was worth a 175-pound reduction. Missing production items included the radio, heater, insulation, headlights, radiator shroud, upholstery, rear bumpers, and cast-iron exhaust manifolds. Racing equipment included 15 x 9.5-inch magnesium wheels with 10.5-inch front and 12.5-inch rear Goodyear racing tires, a ZL2 cold-air-induction hood with hood pins, and L88 fender flares. Header side pipes really opened up the breathing of the radical ZL1 engine.

Duntov himself gave journalists “believer” rides. When coaxed to make a drag-strip run, Duntov clicked off a 12.1-second e.t. at 116 mph, this despite the car’s tallish 3.60 gearing. Lower 4.11 or 4.88 gearing would surely have put the car into the low 11s. Earlier, Duntov had the hood blow off while performing speed test at 180 mph! Later, at GM’s Phoenix test track, journalists got to drive the white mule ZL1 on a short road course. Road & Track writers described its performance as being close to that of a Group 7 race car they had driven shortly before. Duntov’s quasi-ZL1 racer was a shining example of the engine’s potential.

Also on hand at the ‘69 press preview was a menacing-looking Monaco Orange ZL1 wearing 9-inch drag slicks. Although Corvettes were never developed for drag racing, many were quite successful, including the Astoria-Chas L88 and several other Vettes built and raced by Bo Laws. The pumpkin-colored beast at the press event was set up with open headers, a Turbo-400 automatic with a high-stall torque converter, and 4.88:1 gearing. Those lucky enough to be on hand couldn’t have been prepared for the awesome power of the uncorked, big-block ZL1. According to Gib Hufstader, who did the transmission work, powertrain engineer Tom Langdon had tuned this particular ZL1 to produce 710 hp!

So how good was the quarter-mile ride? About 30 guys clicked off 11-second-flat runs, with a best time of 10.89 at 130 mph. Trap speeds are an indicator of plenty of power. Several guys even did neutral starts by revving the engine up to 6,000 rpm and dropping it into gear. Proving grounds PR man Bob Clift said, “We all enjoyed driving that car. Zora used to keep us all excited back then. That was back in the good ol’ days.” A similarly equipped ZL1 Camaro prepared by Dick Harrell went on to run a 10.21 at 133 mph at Kansas City International Raceway.

Duntov turned 65 on December 25, 1974, and a month later he retired from GM. But just six months before retirement, he was thundering around the GM test track in the wildest-looking Corvette mule ever: his wide-body “silhouette racer.” Corvettes were doing quite well in Trans-Am and IMSA racing at the time, with John Greenwood leading the charge. Working with Hufstader and Greenwood, Duntov‘s team developed a body kit to cover the ever-wider racing tires being used in the mid-’70s. Chassis and suspension mods on road-racing Corvettes had progressed far beyond the Z07 off-road suspension and brake packages, but racers were still using variations of the ZL1 and L88 engines.

The silhouette mule was based on a production ‘74 Corvette but was powered by a balanced-and-blueprinted cast-iron ZL1 variant with open-chamber heads, header side pipes, a big Holley double-pumper carb, and an L88 cold-air-induction hood. Clear plastic headlight covers over quartz-iodine headlights were employed, and oil coolers were installed behind the mesh-covered front grille openings. The body-kit parts were riveted on and covered over with 200-mph duct tape. Lowered and wearing magnesium racing wheels, this was one bad-looking Corvette. CARS Magazine editor Marty Schorr got a ride in Zora’s beast and reported, “One day, he took me out on the high-speed oval test track. We were going full tilt, with the tail slightly out, while he had a cigarette in his mouth and was explaining suspension geometry and big-block engine development. He had great control of this animal car.”

As we stated in the beginning of this two-part story, mule Corvettes live hard lives. After tests and evaluations are completed, they always end up in the crusher. Sadly, you just can’t save everything. - KST