How the “24 Hours of GM” Chases the Bugs Out of GM’s Performance Cars

When Chevrolet unveiled the Z/28 last spring, Mark Stielow, its program engineering manager, assured us that the car could burn through a full tank of fuel on a track without overheating any critical fluids. He knew this because his team had done it, repeatedly. But the Z/28's true test is yet to come: While all cars undergo countless months of abuse and a mind-bending battery of tests over millions of miles of development before hitting showrooms, GM treats its high-performance models to something extra. If it's a car that owners might take to the track, engineers subject it to what they call the "24-hour test." Sibling Rivalry The Corvette, CTS-V, new Chevy SS, and even the HHR SS have all endured GM's rigorous 24-hour test at its Milford, Michigan, proving grounds. When the Z/28 enters the crucible later this year, engineers will be comparing it with the ZL1's results, shown here: That's something of a misnomer, as the 24 hours aren't contiguous. According to Aaron Link, the Camaro's lead development engineer, the testing typically happens in sessions lasting up to four hours per day. A team of about 10 drivers, including Corvette Racing Team veterans Ron Fellows and Johnny O'Connell, as well as Link—who has the fastest lap time for the Camaro around both Virginia International Raceway and the Nürburgring's Nord­schleife—aggressively exercise the test mule. Once a driver sets a target hot lap, the goal is for all of them to stay within 2 percent of that time, to keep the car pushing as hard as possible. The drivers take stints of one fuel tank each (30 to 45 minutes, depending on the car). In the parking lot, the team checks fluids, brakes, and tires before a new driver takes over. Nothing but brakes and tires gets changed. That allows any extreme-performance issues to be exposed. "Things don't really have the chance to cool off," says Link. "You find things that you may not have beforehand." If the car does need tires or brakes, the team hoists it on a lift and also conducts a quick visual inspection and a check of the critical fasteners, mainly on suspension components. Comparo: 2013 Chevrolet Camaro ZL1 Convertible vs. 2012 BMW M6 Convertible Instrumented Test: 2014 Chevrolet Corvette Stingray Z51 Dissected: 2014 Chevrolet Camaro Z/28 GM has used Road America, VIR, and the Nürburgring for its 24-hour testing. These days, provided the local weather is hot enough to suitably stress the cars, the tests usually are conducted in-house. GM's track in Milford, Michigan, was designed to ape some of the most challenging corners that exist on race courses around the world. Testing procedures have come a long way since the C4 Corvette underwent GM's first such endurance test in the early 1990s, when engineers measured just 15 data points collected during pit stops. Today's testing monitors 130 channels via telemetry. The one aspect that hasn't changed, though, is that the 24-hour test is grueling. And, from the looks of it, a ton of fun. Behind the Blue Oval Ford's endurance course Chevy's crosstown rival has a similar curriculum for its high-performance models. Past Shelby and SVT models ran 12-hour tests designed to mimic the abilities of the average customer, rather than those of professional drivers. So far, the Ford GT and 2013 Shelby GT500 are the only Blue Oval products to endure a full 24-hour battery. Ford's European RS Team tests its models for 3100 miles on the Nürburgring and for 1550 miles around Italy's high-speed Nardo Ring. from Car and Driver Blog http://blog.caranddriver.com

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