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Motor Trend confirms botched dyno test for C8 Corvette

The dyno operator had the system set for all-wheel drive and used an incorrect road-load estimate.

Motor Trend has confirmed that dynamometer operator error and an incorrect estimate of an unknown parameter led the magazine to conclude that the 2020 Corvette "produces more power than Chevrolet claims."

The most glaring screwup was traced to a drivetrain configuration setting that was switched to all-wheel drive, which led the dyno computer to assume much higher friction losses than the rear-wheel-drive Corvette would suffer from.
The test also used the C7 generation as a placeholder for road-load horsepower at 50 mph, which provides a reference to both aerodynamic drag and friction. There is apparently a 22 percent difference between the factor for the C7 and C8, which was only clarified after General Motors provided the correct figure for the latest model.
"These two factors conspired make the dyno believe the Corvette's powertrain was overcoming way more inertia than it really was, which led to the inflated results," MT says.
The magazine also conducted "road-dyno" tests using a Vbox to assess power output in a track setting, resulting in an estimated 395 horsepower and 350 pound-feet of torque at the wheels. A 15-percent friction loss would put the car at 454 horsepower and 403 pound-feet of torque at the crankshaft, just slightly below the SAE-rated official specs of 465 horses and 412 pound-feet.

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