We're well aware of the awesomeness of the engine found in the BMW M5 and M5 Competition, code name S63B44T4. The twin-scroll turbochargers nestled between the 4.4-liter V-8's cylinder banks pressurize the combustion chambers with 25.9 psi at max boost. BMW rates the base engine at 600 horsepower and the Competition model's at 617 horsepower—at the crankshaft—with both making 553 lb-ft of torque.

Michael Simari Car and Driver

All those ponies make the all-wheel-drive sedan savagely quick. In our tests, both the M5 and M5 Competition have reached 60 mph in less than three Mississippis and have conquered the quarter-mile in 11.0 seconds or less. Given that both cars weigh in excess of 4200 pounds, we've long suspected that BMW may be understating their outputs. So, we decided to put an M5 Competition on a rolling dynamometer—colloquially known as a "dyno"—to see if our suspicions were warranted.

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.

Dyno test results show peak hp of 617 hp at the wheels. Car and Driver

A look at the test result graph shows an impressive plateau of torque that starts at about 2100 rpm and stays nearly flat all the way to 5000 rpm, tapering off slightly after that. If you're wondering why the graph shows a sudden drop at 6000 rpm, that's where the M5 hits its 162-mph governor in sixth gear. BMW lists peak horsepower at 6000 rpm, so it's likely all she had, but given that the engine revs another 1200 rpm, there is a chance the engine had more to give. But probably not much, considering the torque started its descent 1000 rpm earlier.

Michael Simari Car and Driver

Are we shocked that BMW might underestimate its claimed output figures? Not really. Most carmakers are conservative in the output figures they quote. But this overabundance helps explain how a mid-size sports sedan weighing more than two tons can run a quarter-mile nearly as quickly as a 3381-pound Ford GT claiming 647 ponies.



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