ATLsupra
08-21-2008, 05:47 PM
http://www.caranddriver.com/features/columns/c_d_staff/larry_webster/what_is_the_gt_r_s_real_horsepower_column?cid=259
“It’s a ringer,” we said among ourselves as soon as the first Nissan GT-R’s test results were in. Despite a power-to-weight ratio that’s 30 percent worse than that of the similarly priced Corvette Z06, that first GT-R outran the Z06 to 60 mph (3.3 seconds versus 3.4 for the quickest Z06 we’ve tested) and through the quarter-mile (11.5 at 124 mph versus 11.8 at 125). Even allowing for the launch advantages of all-wheel drive, the GT-R’s performance made us suspicious. It wouldn’t be hard for Nissan engineers, we surmised, to crank up the boost and thus jack up horsepower that would result in astonishing track numbers in American car-magazine tests. The GT-R was in such demand and our allotted time with it was so short, however, that we didn’t have time to strap it onto a chassis dyno and measure the horsepower.
We soon tested two more GT-Rs, and supporting our suspicions, they were considerably slower. GT-R No. 2 was 0.6 second behind the No. 1 through the quarter, and GT-R numero tres was a disturbing 1.1 seconds slower. Again, we didn’t have enough time to dyno-test those cars, but it seemed clear that the first GT-R was likely a one-of-a-kind rocket.
We finally got the opportunity to run a GT-R on a chassis dyno in May after Tony Swan returned with the example he used for the One Lap of America competition. The only problem with that car—No. 4 in our series—was that it performed about as well as the first. There were some differences, as you can see in the chart below, but those can easily be chalked up to the fact that the cars were tested on different days at different tracks. Yes, we do perform a weather correction to account for much of the ambient-condition difference, but no correction is perfect.
A brief primer on the Mustang chassis dyno we used: Picture a pair of parallel, supersized rolling pins mounted in the floor. The car is strapped down so that the front wheels are on one roller and the rears on the other. The operator puts the car in gear and, via the tires, spins these rollers, which are attached to a device that measures the applied force. A computer that ties into the car’s diagnostic plug and reads engine rpm calculates the horsepower. This power figure is what’s known as “wheel horsepower,” and it’s less than the engine horsepower that’s listed in our specs because the drivetrain components—transmission, driveshafts, bearings, differential—all have internal friction that soaks up power. How much power is lost in the journey to the road is not accurately known, but a 15-percent loss for rear-drive cars with manual transmissions and a near 20-percent loss for four-wheel-drive cars are good estimates.
On MotorCity Speed’s Mustang dyno in Commerce Township, Michigan, GT-R No. 4 produced a peak of 415 horsepower at the wheels. Based on our 20-percent loss estimate, the engine output was 519, or 39 horsepower more than Nissan’s stated 480.
So what’s up? We called Nissan, and the company says the first four cars we tested were early-build versions that received regular engine-computer software updates, which may account for the varied results we recorded. We then wondered which engine-computer calibration was the one real-world GT-R buyers would receive.
Three weeks later, a fifth GT-R arrived. This one, allegedly, was a production version with the latest—and final—engine calibration. We took it both to the test track and MotorCity’s dyno.
This car performed nearly identically to the fourth car. It smoked the quarter-mile in 11.6 seconds at 120 mph and produced 420 wheel horsepower. We also measured the turbo boost pressure in both cars, and the curves were basically identical.
Though we didn’t get a chance to dyno-test the two slower GT-Rs, three of the five were so close in performance that we believe they accurately represent the GT-R’s capability. Clearly, Nissan is delivering more than the advertised 480 horsepower. And the most likely figure is about 520, which is yet another reason to bow to the best performance value since the Corvette Z06.
“It’s a ringer,” we said among ourselves as soon as the first Nissan GT-R’s test results were in. Despite a power-to-weight ratio that’s 30 percent worse than that of the similarly priced Corvette Z06, that first GT-R outran the Z06 to 60 mph (3.3 seconds versus 3.4 for the quickest Z06 we’ve tested) and through the quarter-mile (11.5 at 124 mph versus 11.8 at 125). Even allowing for the launch advantages of all-wheel drive, the GT-R’s performance made us suspicious. It wouldn’t be hard for Nissan engineers, we surmised, to crank up the boost and thus jack up horsepower that would result in astonishing track numbers in American car-magazine tests. The GT-R was in such demand and our allotted time with it was so short, however, that we didn’t have time to strap it onto a chassis dyno and measure the horsepower.
We soon tested two more GT-Rs, and supporting our suspicions, they were considerably slower. GT-R No. 2 was 0.6 second behind the No. 1 through the quarter, and GT-R numero tres was a disturbing 1.1 seconds slower. Again, we didn’t have enough time to dyno-test those cars, but it seemed clear that the first GT-R was likely a one-of-a-kind rocket.
We finally got the opportunity to run a GT-R on a chassis dyno in May after Tony Swan returned with the example he used for the One Lap of America competition. The only problem with that car—No. 4 in our series—was that it performed about as well as the first. There were some differences, as you can see in the chart below, but those can easily be chalked up to the fact that the cars were tested on different days at different tracks. Yes, we do perform a weather correction to account for much of the ambient-condition difference, but no correction is perfect.
A brief primer on the Mustang chassis dyno we used: Picture a pair of parallel, supersized rolling pins mounted in the floor. The car is strapped down so that the front wheels are on one roller and the rears on the other. The operator puts the car in gear and, via the tires, spins these rollers, which are attached to a device that measures the applied force. A computer that ties into the car’s diagnostic plug and reads engine rpm calculates the horsepower. This power figure is what’s known as “wheel horsepower,” and it’s less than the engine horsepower that’s listed in our specs because the drivetrain components—transmission, driveshafts, bearings, differential—all have internal friction that soaks up power. How much power is lost in the journey to the road is not accurately known, but a 15-percent loss for rear-drive cars with manual transmissions and a near 20-percent loss for four-wheel-drive cars are good estimates.
On MotorCity Speed’s Mustang dyno in Commerce Township, Michigan, GT-R No. 4 produced a peak of 415 horsepower at the wheels. Based on our 20-percent loss estimate, the engine output was 519, or 39 horsepower more than Nissan’s stated 480.
So what’s up? We called Nissan, and the company says the first four cars we tested were early-build versions that received regular engine-computer software updates, which may account for the varied results we recorded. We then wondered which engine-computer calibration was the one real-world GT-R buyers would receive.
Three weeks later, a fifth GT-R arrived. This one, allegedly, was a production version with the latest—and final—engine calibration. We took it both to the test track and MotorCity’s dyno.
This car performed nearly identically to the fourth car. It smoked the quarter-mile in 11.6 seconds at 120 mph and produced 420 wheel horsepower. We also measured the turbo boost pressure in both cars, and the curves were basically identical.
Though we didn’t get a chance to dyno-test the two slower GT-Rs, three of the five were so close in performance that we believe they accurately represent the GT-R’s capability. Clearly, Nissan is delivering more than the advertised 480 horsepower. And the most likely figure is about 520, which is yet another reason to bow to the best performance value since the Corvette Z06.