We photographed the Sundowner earlier this year at the Petersen Museum in LA, where it was
Standing solemnly on the Bonneville Salt Flats at sunset, actor Sir Anthony Hopkins uttered a classic line in one of the best motorsports films ever made: “This is sacred ground.” He effortlessly evoked speed-bike racer Bert Munro in The World’s Fastest Indian, based on “One Hell of a True Story” (as the movie’s promo poster boldly proclaimed).
Anyone who’s joined the 200-mph club can relate. Just ask Duane McKinney, who drove a ’68 stock-bodied Corvette to a record-setting 240 mph.
Leading up to this crowning achievement, McKinney set several other records as far back as the mid ’70s. What makes them all the more astonishing is that they were done in a stock-bodied passenger car. Not only that, but it was running a production-series, iron-block V-8. On gasoline. Naturally aspirated, too. And the tranny was a four-speed. All told, this feat was roughly akin to breaking the speed of sound in a wooden sailing ship—with its oars still in the water.
That’s because as sleek as the C3 looked, its aerodynamics were actually a step back from the C2, the first Corvette to have its lines refined by wind-tunnel testing. For proof, take note of an intriguing article in the May 2009 issue of Corvette Fever (formerly our sister pub before it merged with VETTE). In a comparison of the aero characteristics of every Corvette body style from C1 through C6, the Cd (coefficient of drag) of a ’70 model was found to be as bad as the C1’s, and even worse than the C2’s. So basically the ’68 body shape had only slightly better aerodynamics than a shoebox.
To be fair, these same wind-tunnel tests revealed that the addition of the tiniest rear spoiler did help produce 13.9 pounds of downforce in the rear, making the C3 the only Corvette that was able to produce negative lift numbers. (That’s not counting the C7 Stingray, which has gone through extensive aerodynamic testing, as noted in our series on this new design.)
Even so, Corvette engineer Zora Arkus-Duntov wanted the Sting Ray’s replacement to be smaller, leaner, and more aerodynamic, ideally with a rear- or mid-mounted engine. Designer Bill Mitchell, on the other hand, loved to make cars look aerodynamic, without necessarily being so in reality. Ultimately, the C3’s coke-bottle curves were a victory of Mitchell over Duntov, of style over substance. And for all its failings, it also sold remarkably well.
McKinney found an unsuspecting ’68 C3 on a used-car lot in February 1975, and fellow racer Bob Kehoe drove it home, toward a much higher calling. First, those problematic aerodynamics had to be addressed before taking the car to Bonneville later that same year, where it hit 166 mph in D/GT.
Breaking through wind resistance would come down to a matter of brute force, one that required the services of a seasoned engine builder who knew more than a thing or two about hurtling over the Salt Flats at ungodly speeds—sacred ground or otherwise. But that individual would have to wait.
First, McKinney had to figure out how to avoid an unwanted takeoff from the Flats. His method was crude yet fairly effective—lead. Lots and lots of lead. Everywhere you look, under the nose, behind the seats, in the back end, he added thick, gray plates, stacked like pancakes at a VFW fundraiser. And to make sure the car wouldn’t skitter around like a shopping cart with wobbly wheels, the caster angle was increased with washers on the control-arm mounts, to a total of nine degrees.
After all, 200 mph on the Salt is no joke. It’s nothing like 200 mph in the quarter-mile (which is no joke either, but a wholly different scenario). We’re talking about running miles at speed, not merely for a few seconds. As for velocity, imagine covering the length of a football field in about the time it takes to blink.
In addition to the aero issues already noted, there are traction issues, steering issues, and don’t forget engine-reliability issues. Also, Bonneville is at a higher altitude, so you have to tune for lower air density, temperature, humidity, and so on.
Speaking of engine tuning, who cooked up the mill for breaking the double-century mark? He would be none other than performance sage Gale Banks. Banks is mostly known today for an impressive array of upgrades for diesel engines, but before he turned his attention to oil burners, he employed forced induction on gasoline mills to an extreme degree, along with more than a few other tricks. He can lay claim to a slew of land and marine speed records in several categories. Interestingly, it was the sale of his beloved ’63 Corvette that gave him the financial means to open a much larger shop and begin designing and selling performance parts.
The Sundowner project, as it came to be known, would eventually spend months and months in Banks’ shop getting breathed on heavily. The Banks crew, led by Gale and Bob Robe, were joined by Duane McKinney and Bob Kehoe, who prepped the car. Despite their best late-night efforts, they didn’t have time to get the turbo system done. Given all the after-hours wrenching, along with the late-afternoon runs on the Salt, the name Sundowner was altogether fitting.
After some head scratching, Banks came up with an intercooler to increase the air density—without a turbo. All in order to force-feed a four-barrel Dominator mounted on the single-quad intake. It was fitted on a 430ci block (achieved by boring a 427 0.010 over) with iron cylinder heads and 12.5:1 pistons. Banks started by cutting holes in the radiator core support to duct more air into the intercooler, which used liquid carbon dioxide as a cooling medium.
“The secret to CO2 is to put an expansion valve at the intercooler inlet,” Banks explains. “That way it stays liquid up to the valve, and the orifice limits the max flow rate.” That would lower the temperature of the intake air from as high as 105 degrees (F) down to 30 or even less. And for every 10-degree drop in temperature, he points out, there would be a nominal one-percent increase in air density.
Crude but effective: To combat high-speed lift, the Sundowner crew deployed ballast, in th
But this single device didn’t solve all the problems. The 1-inch rubber hoses that dumped spent CO2 underneath the car would freeze and crack, then break off. So the race crew had to scrounge around the nearby town of Wendover, Utah, to find elbows and electrical conduit that could withstand the low temps.
Another challenge caused by the chilling was the tendency of the carburetor, which was mounted inside a custom-fabricated ram-air plenum, to ice up. The engine wouldn’t run with the carb frozen, so the CO2 wasn’t activated until Third gear.
Once all those hurdles were overcome, “It made great power, and the Kehoe-McKinney and Banks Corvette set a new record at Speedweek 1979 of 210-plus,” Banks notes. “That was with no turbo—just intercooling. It was the fastest single-four-barrel Corvette on the planet!”