C8 Power Discrepancy: Are the offiical numbers under-rated?

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Thread: C8 Power Discrepancy: Are the offiical numbers under-rated?

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    4.4 Liter Supercharged Northstar IROCNROL1's Avatar
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    C8 Power Discrepancy: Are the offiical numbers under-rated?

    Seems testing is coming up with higher than stated numbers.

    How Much Power Does the 2020 Chevrolet Corvette Really Make? We Take it to the Dyno and Find Out
    A lot more, it turns out
    Miguel Cortina, Words
    Motor Trend Staff, Photos
    Oct 21, 2019
    motortrend.com

    I'm looking through a window, hands around my face, staring at a screen with all sorts of graphics and numbers that are too small to read. On the other side of the window, a red 2020 Chevrolet Corvette is strapped to the dyno with its rear wheels spinning very, very fast.

    The double-paned windows are not enough to keep the engine note from reaching other parts of the facility. The speedometer on the screen reads 150 mph, but the front wheels are not moving at all. Once the engine noise winds down and the wheels stop spinning, the numbers we're looking for pop up on the screen—558 hp and 515 lb-ft of torque at the wheels. "We've got a hot rod!" says international bureau chief Angus MacKenzie, who has been standing next to me all this time.

    We're in shock. A quick math check reveals that's an estimated 656 hp and 606 lb-ft of torque at the crank if we assume a 15-percent drivetrain loss—way over the 495 hp and 470 lb-ft that Chevy claims. (That 15 percent represents the power consumed by everything between the engine crankshaft and the drive wheels, including inertia of all the spinning parts, power to run the hydraulic pump in an automatic or twin-clutch transmission, the drag that occurs when gears spin through lubricating oil, friction between the gear teeth, etc. It's an educated guestimate frequently used across the industry for modern light-duty automatic transmissions—manuals experience slightly smaller losses; older or heavier-duty automatics slightly larger ones.)

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    Last edited by nadepalma; 10-23-2019 at 09:50 PM. Reason: Revised and reformatted; moved to newsticker
    It sounded pretty good until I actually said it.

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    Re: C8 horsepower discrepancy?

    Cool News!

    GM can shake the Market Up, now it just has to do this stuff with a Bigger Market! Dodge Caravan/Ford Taurus/Chrysler K Car/Ford Explorer kind of Market.

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    Re: C8 horsepower discrepancy?

    This is GM, they SAE certifiy everything, including speedometers, whet they tell you is what you get. Someone needs a new dyno. The secret is a DCT and high torque motor, not numbers gaming.

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    Re: C8 horsepower discrepancy?

    Everything I am reading says MT just plain screwed up. Either the 0-60/100 times are wrong or the dyno is wrong. Given the times matched GM, they messed up the dyno measurement. Really sad. You'd think they would have scratched their heads and said this is wrong, cannot be right. But then they are journalists and not engineers.

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    6.2 Liter LS3 V8 posaune's Avatar
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    Re: C8 horsepower discrepancy?

    Quote Originally Posted by Vagon11 View Post
    Everything I am reading says MT just plain screwed up. Either the 0-60/100 times are wrong or the dyno is wrong. Given the times matched GM, they messed up the dyno measurement. Really sad. You'd think they would have scratched their heads and said this is wrong, cannot be right. But then they are journalists and not engineers.
    Or they ran with the screwed up numbers to increase the number of clicks the article will get. Sometime later they will correct or post another article correcting to gain more clicks.
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    Re: C8 horsepower discrepancy?

    Quote Originally Posted by Vagon11 View Post
    Everything I am reading says MT just plain screwed up. Either the 0-60/100 times are wrong or the dyno is wrong. Given the times matched GM, they messed up the dyno measurement. Really sad. You'd think they would have scratched their heads and said this is wrong, cannot be right. But then they are journalists and not engineers.
    I believe the 0-60 times have already been independently verified, so I'm guessing their dyno is faulty.

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    Re: C8 horsepower discrepancy?

    their assumption is 15% drivetrain losses. perhaps the dct trans is much more efficient and other losses are less than expected. also maybe ringer or super-tuned version

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    Re: C8 horsepower discrepancy?

    Quote Originally Posted by Dr.Show-Me View Post
    their assumption is 15% drivetrain losses. perhaps the dct trans is much more efficient and other losses are less than expected.
    That doesn't explain how it made more hp to the wheels than the advertised crank hp.

    The dyno could definitely be the problem. That's an awful big leapfrog from one year to the next with the same NA engine architecture. Let's just hope it's not a ringer for initial testing purposes only. I don't think GM would be dumb enough to try and pull a fast one by supplying a ringer because it gets found out and the lingering bad press is not worth the initial praise.
    Last edited by big swede; 10-23-2019 at 12:47 PM.

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    Re: C8 horsepower discrepancy?

    I read in another article that I can't find now where GM said that they SAE tests are very stringent and that normal testing will likely present better results. Specifically, SAE uses warmer than normal air and that the engine is very responsive to colder air. They speculated that this caused the difference reported by MT.
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    Nope, this is just a bad dyno reading. Unless this is somehow repeated with other dynos then I will question otherwise.

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    Re: C8 horsepower discrepancy?

    Quote Originally Posted by TruckMan View Post
    I read in another article that I can't find now where GM said that they SAE tests are very stringent and that normal testing will likely present better results. Specifically, SAE uses warmer than normal air and that the engine is very responsive to colder air. They speculated that this caused the difference reported by MT.
    Colder air couldn't have possibly given this particular C8 200 more hp
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    Re: C8 horsepower discrepancy?

    Quote Originally Posted by sdotjeezy View Post
    Colder air couldn't have possibly given this particular C8 200 more hp
    Yes, you need stickers and a huge wing on the back for those type of numbers...one of those tornado intake inserts too.
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    Re: C8 horsepower discrepancy?

    Quote Originally Posted by big swede View Post
    That doesn't explain how it made more hp to the wheels than the advertised crank hp.

    The dyno could definitely be the problem. That's an awful big leapfrog from one year to the next with the same NA engine architecture. Let's just hope it's not a ringer for initial testing purposes only. I don't think GM would be dumb enough to try and pull a fast one by supplying a ringer because it gets found out and the lingering bad press is not worth the initial praise.
    I saw an article over my head that was saying for the redline of the engine, the size of the engine, it was thermodynamically impossible for that hp number. Not a mechanical engineer, but the author seemed to know what they were talking about. The takeaway from the article was without forced induction, not possible.

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    Re: C8 horsepower discrepancy?

    Or Chevy is sandbagging and the engine is just that powerful.

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