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We get many inquiries regarding the difference between factory rated power at the flywheel vs. the power a car puts down once it gets to the wheel. I think this would be an ideal time to explain, so let's jump into our flywheel lecture, using a bone-stock 2009 Mercedes C63 as our lecture.

Out of the box Mercedes rates this 6.3L normally aspirated 32 valve V8 at the engine/flywheel: 451 HP and 443 TQ

Since Mercedes rates power at the flywheel, and we measure power at the wheels, there is going to be a percentage of parasitic loss due to drivetrain friction from the flywheel all the way down to the wheels. Think about it, once the power is transferred from the engine's crank shaft, through the torque converter, through the transmission gears, through the drive shaft and U-Joints, through the rear differential, through the rear axles and CV joints, through the rotating mass of the wheels and brakes and finally, all the way down to the friction of the tires on the dyno rollers. Still with us? This is where our dyno FINALLY measures the power. And through all of this, we see an approximate powertrain loss of 25% loss.

NOTE: Every dyno measures horsepower differently when it comes down to different types and manufacturers of dynos. Our dyno uses a current based load- like a generator but in reverse. The harder a car pushes the power down to the dyno, the harder our dyno pushes back with more and more load in order to maintain a consistent load through the entire power band.

This creates a REAL WORLD load (as if you were driving on the street). For over a decade of dyno tuning experience, Dyno-Comp knows what our powertrain loss factor is on a 2WD A/T transmission car, and that is 25 to 27%. Let's use 25% so we are on the conservative side.

So, on a car that is rated at 450 HP at the flywheel, we SHOULD see approximately 360 HP at the wheels. Here's the math: 360 X 1.25 = 450 HP

So let's put this formula to the test.


REAL WORLD this is what a 2009 C63 AMG put down on our dyno:

  • 366 (Wheel HP) X 1.25 = 457.5 HP at the flywheel. This is about 6.5 HP more than stock.
  • 350 (Wheel TQ) X 1.25 = 437.5 TQ at the flywheel. This is about -5.5 HP less than stock.

    This particular C63 AMG was a bit on the strong side for HP but a bit less for TQ. At the end of the day, this is pretty close, 6 of 1, half dozen of another!

  • HP is now at 450 (at the wheels), which equates to approximately 562 HP at the flywheel.
  • TQ is now at 400 (at the wheels) which is approximately 500 TQ at the flywheel.

    WHEN THE DUST SETTLES, what does this all mean?

  • +105 HP increase at the flywheel
  • +63 TQ increase at the flywheel


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