Our test car was a fully broken-in (1275 miles) early-production Z51 coupe, equipped with the NPP dual-mode performance exhaust, which reduces back-pressure by a whopping 80 percent at high engine speeds, adding six peak horsepower and four pound-feet, bringing the totals to 436 and 428, respectively. Naturally, we opted for the revised Tremec six-speed manual transaxle creating what is now the second best performance Corvette. Gearing in the Z51 is nine to 14 percent shorter in the first four gears relative to the base manual, and while the base six-speed paddle-shifted automatic matches the Z51's gearing in first, the other gears are 12 to 25 percent taller. Automatic buyers can opt for a slightly shorter axle ratio (2.73:1 versus 2.56:1), which doesn't have much effect on the performance numbers, but improves in-gear passing acceleration. GM reckons the automatics should trail our Z51 stick by about a tenth to 60 mph, two-tenths and two mph in the quarter. We wheedled and cajoled for a chance to verify these projections using our photo car, but because it was so green (300 miles), GM said no dice.
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