C8 Corvette Dyno Numbers Explained by Motor Trend
Initial C8 Corvette dyno numbers were impossibly high due to incorrect dyno settings.
When Motor Trend announced their initial dyno test results for the C8 Corvette, the automotive world stood still. The outlet loaded the new Stingray onto a dyno during an impromptu run to a local performance shop. They expected good numbers. They got incredible numbers. In fact, the initial C8 dyno numbers were so incredible that many people knew that something had to be wrong with the dyno.
Meanwhile, some people believed that the C8 Corvette is actually underrated by more than 100 horsepower Sadly, based on Motor Trend’s latest report, that is not the case.
Corvette Dyno Numbers
When Motor Trend first tested the 2020 Corvette Stingray Z51 on the dyno, their first horsepower reading was 558 at the wheels. That is not a valid number for a car that offers 495 horsepower at the engine. The dyno operator made some changes and the number would come down over the course of several runs, bottoming out at 478 horsepower. If we use a 15% drivetrain loss factor, a car with 478 rear wheel horsepower has around 563 horsepower at the crankshaft.
Did Chevrolet underrate the C8 LT2 output by nearly 70 horsepower? No, the dyno was setup incorrectly.
Dyno Setting Errors
When Motor Trend tested the 2020 Corvette, not all of the key information needed for a dyno run was available. Most notably, the dyno operator didn’t know what road-load factor to use, so he used the number from the C7. Motor Trend has since learned that the operator should have been using a factor of 15.4, but he was using 12.6. This factor played a role in the dyno numbers being artificially high.
Next, the dyno used to test the C8 Corvette was set up for an all-wheel-drive vehicle. The dyno computer knows how much the rollers weight and it knows how much force is needed to spin them. In the case of the C8 testing, the computer thought that the car was spinning the front and rear rollers. Since it was only spinning the rear roller, the computer thought that the LT2 was producing far more power.
Between the all-wheel-drive setting and the incorrect road-load factor, the C8 Corvette dyno test had little change of producing an accurate number.
New C8 Power Numbers
Once Motor Trend realized the errors with their initial C8 Corvette dyno testing, the crew wanted to come up with more realistic numbers for discussion.
The outlet started by analyzing data logs from their best drag strip runs with the C8 Corvette. The team figured out how much power was used by looking at the time taking to accelerate in third, fourth and fifth gear and comparing that to the mass of the vehicle. When they plotted all of those numbers on a graph, they came up with a smoothed curve that peaks at 425 horsepower. A car with a 15% drivetrain loss ratio and 425 wheel horsepower would make around 500 horsepower at the crankshaft. That makes 425 wheel horsepower the most reasonable number that we have seen, but it is based on the 15% drivetrain loss assumption.
Finally, Motor Trend hooked up a VBox in a different C8 Corvette and did some hard pulls. Using the acceleration data, the system reported 395 horsepower at the rear wheels. The 15% drivetrain loss factor at 395 horsepower would only lead to 465 horsepower. This number can be disregarded. It is far too low to be reasonable.
In the long run, we still don’t know for sure how much power the C8 Corvette makes at the wheels. The calculated figure of 425 is the most reasonable. In the end, all that really matters is that the new Stingray is crazy-quick.
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