Does the C8 Really Make 656 HP?

495 hp. That’s what Chevrolet says the C8 Corvette can make when it’s equipped with the performance exhaust. But is that an accurate figure, or is the C8 hiding some ponies? After all, under three seconds to 60 is purdy dang quick for just 500 hp and two driven tires. Well, if you want a second opinion, Motor Trend has taken the new Corvette to a dyno.

558 hp and 515 lb-ft of torque. That’s what the magazine’s dyno run showed. And that’s power at the wheels, so if you take into account the usual 15 percent losses to the gearbox and diff, that puts you somewhere around 656 hp and 606 lb-ft of torque at the crank. But could the C8 really be making 160 hp more than quoted by GM?

Strapped down on a Mustang dynamometer, the car was tested in fifth gear. Why fifth, you ask? It’s because that’s the closest gear to 1:1, and for accurate numbers, you need to test your run in the direct-drive (or closest) gear. A sixth-gear run (out of eight in the transmission) showed 478 hp and 536 lb-ft on the dyno, so you can see how much of a difference gearing makes.

But still, Motor Trend later found out that at 0.953:1, fifth was the closest gear to 1:1. What gives? Chevrolet told them that the official figure is certified to SAE spec J1349, which sets out the exact testing procedure. It uses a pull that slowly increases RPM, letting the engine stabilize at each step, rather than the one wide sweep most testing uses. If you’re wondering about correction factors, which can be tweaked to make numbers look more appealing, Motor Trend says this dyno ran an 850 lb-ft rated Ram 2500 diesel and got 890 lb-ft at the wheels, which is definitely close enough.

So does the C8 make 495 hp? Yes. Does it make 656 hp? Also yes. How does that work? Well, that’s why automakers do extensive testing and bring in specialized engineers to run the testing. How much power does it really make? We may never know, but Chevrolet guarantees that it makes at least 495 hp, and with an SAE test that means they all need to make that all the time, it could be a touch conservative.

Motor Trend

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