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    • Car and Driver finally figures out BMW underrates the F90 M5 and turbo motors but is confused by drivetrain losses - 2019 M5 Competition 617 awhp

      Stop the presses, BMW is underrating the F90 M5! Thank you so much Car and Driver for bringing this to our attention in May of 2019. I wonder if anyone looked into this with the previous generation F10 M5 almost a decade ago? Maybe this is nothing new for BMW?


      It isn't. BMW started this trend with the N54. Why? Well, the turbo 3-Series made E46 M3 power and BMW did not want to upset the delicate balance that is placating M owners while transitioning to turbochargers.

      BMW used to cling to a 15% drivetrain loss rule on a Dynojet right on the money. The E46 M3, E92 M3, E60 M5, etc., all were right at 15%.

      With 617 all wheel horsepower the F90 M5 obviously is making more than the 617 horsepower it is rated it. Is the F90 M5 somehow producing negative or zero losses? Of course not.

      With an all wheel system the losses are at least 15% and closer to 20%. Let's just use that 15% rule of thumb and it works out to a conservative 725 crank horsepower. Yes, conservative.


      Quote Originally Posted by Car and Driver
      For our experiment, we put a stock M5 Competition on a Dynojet all-wheel-drive dynamometer at Livernois Motorsports and Engineering in Dearborn Heights, Michigan. To avoid any torque multiplication by the car's eight-speed transmission, we ran the test in sixth gear, which is a direct-drive or 1.00:1 ratio. The results show a surprising peak of 617 horsepower and 606 lb-ft of torque at the wheels. Modern drivelines are very efficient at transferring torque, so we're not convinced this is a 700-hp engine at the crank, but it's darn close.
      Car and Driver is not convinced the F90 M5 is a 700 horsepower car stock because apparently they are bad at math. They state the F90 M5 accelerates as quickly as a 647 horsepower and 3381 pound Ford GT. Well, then it needs to be over 700 horsepower as the Ford GT power to weight ratio is 5.22 lbs per hp.

      The F90 M5 at 4200 pounds to match 5.22 lbs per hp would need 804 horsepower.

      This isn't complicated guys. The F90 M5 Competition is well over 700 horses.

      This article was originally published in forum thread: Car and Driver finally figures out BMW underrates the F90 M5 and turbo motors but is confused by drivetrain losses - 2019 M5 Competition 617 awhp started by Sticky View original post
      Comments 7 Comments
      1. Arin@APR's Avatar
        Arin@APR -
        Percentages overinflate numbers. So do correction factors on stock dynos. Bet it’s close to 650 crank, stock.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by Arin@APR Click here to enlarge
        Percentages overinflate numbers. So do correction factors on stock dynos. Bet is close to 650 crank, stock.
        Not based on the historical Dynojet rule of thumb.

        Plus, these things are immensely powerful. The trap speed for the weight tells us it HAS to be over 700 horsepower.
      1. Arin@APR's Avatar
        Arin@APR -
        FWIW, the rule of thumb doesn’t work. It would suggest as the same car makes more power, it some how requires eating up more power to turn the same drivetrain.

        I did a little digging. Several European “crank” synod show around 650 stock, uncorrected, especially when removing the slight overshoot.

        Mind you, certified oem crank calculations are not generated on a normal dyno / through a normal pull. It involves picking several rpm points and running full load at those points for a long period of time.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by Arin@APR Click here to enlarge
        FWIW, the rule of thumb doesn’t work. It would suggest as the same car makes more power, it some how requires eating up more power to turn the same drivetrain.
        I agree it isn't accurate but it is a point of reference as to where cars were output wise. If the E60 M5 was 507 horsepower at 430 rwhp than the F90 M5 at 617 awhp is well over 700 crank.

        Click here to enlarge Originally Posted by Arin@APR Click here to enlarge
        I did a little digging. Several European “crank” synod show around 650 stock, uncorrected, especially when removing the slight overshoot.
        I've studied this extensively Arin and if you're referring to the MAHA it is way, way more conservative than the Dynojet. If you look at older M5's on that dyno it is the same thing though, the turbo M5 versions are making way more power than advertised.

        Click here to enlarge Originally Posted by Arin@APR Click here to enlarge
        Mind you, certified oem crank calculations are not generated on a normal dyno / through a normal pull. It involves picking several rpm points and running full load at those points for a long period of time.
        For sure and this is how BMW gets away with it I think.
      1. RNS-11Z's Avatar
        RNS-11Z -
        Sticky, if I’m making 730rwhp on a Maha, what would it be on a dyno jet?
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by RNS-11Z Click here to enlarge
        Sticky, if I’m making 730rwhp on a Maha, what would it be on a dyno jet?
        No idea but that would be a ton.

        The wheel output on MAHA's is extremely conservative. It's usually the blue line, not red.
      1. Arin@APR's Avatar
        Arin@APR -
        MAHA wheel is dramatically different than other dynos because it doesn't assume any losses at all , where as other dynos have a general amount built in. That's why the MAHA has a coast down test at the end. It's also why other dynos, like mustangs, have the ability to do the coast down to get bearing / strapping losses before a session (though most everyone skips this, and just uses the default value). Technically wheel vs wheel from dyno to dyno should be different, sometimes by quite a bit, but at the crank, the same car should be making technically about the same power.