BMW famously underrates its engines, especially in M cars. Which is why whenever a new M car comes out, YouTuber rush to bring them to dynos to find their true power and make videos with catchy headlines, like “BMW LIED! M2 Makes a Gazillion HP!!1!!” or something like that. However, it is actually interesting to see how much power BMW M engines actually make. And BMW isn’t the only brand to do that, as most German brands are pretty conservative with their claimed power figures. So how do they all compare when rubber meets dyno?
What’s ironic about this test is that three of the cars actually use variations of the same engine. The Audi RS Q8, Porsche Cayenne Turbo GT, Lamborghini Urus Performante all use the Volkswagen Group’s ubiquitous 4.0-liter twin-turbocharged V8. All three cars are tuned differently and have different power figures but they all start with the same base.
On paper, the Lambo is the most powerful of the group, making a claimed 657 horsepower and 627 lb-ft of torque. Next up is the Porsche Cayenne Turbo GT, with 631 horsepower and 626 lb-ft of torque. Then comes the BMW X5 M, which makes 617 horsepower and 553 lb-ft of torque from its 4.4-liter twin-turbo V8. Weakest on paper is the Audi RS Q8, which makes 591 horsepower and 590 lb-ft. All four cars use a version of ZF’s brilliant eight-speed automatic, just with their own state of tune, and all-wheel drive.
For the layman, all dyno machines measure wheel horsepower, or how much power is actually being put to the wheels. Car manufacturers typically measure horsepower at the engine’s flywheel, which is always more than wheel horsepower, as engine power is lost by going through the transmission, driveshafts, differentials, and axles. Those parasitic power losses can be quite high, especially with automatic, all-wheel drive vehicles. So after the dyno measures the car’s wheel horsepower, a calculation needs to be done to figure out how much flywheel horsepower the engine is actually making and then compare that figure to the manufacturer’s claimed figure, to see how the two differ.
All four cars are overachievers, making quite a bit more than their factory claimed figures. The question is which one overachieves the most?