Tested: 2020 BMW M550i xDrive Gets Another Go at the Test Track

UPDATE 5/14/21: This review has been updated with revised test results from the M550i's second visit to the test track.

When we last checked in with the BMW M550i we were a bit puzzled by its slower-than-anticipated acceleration numbers. BMW claims a zero-to-60-mph time of 3.6 seconds yet our test car needed 4.1 seconds to hit that mark. Heavier BMWs with identical 523-hp twin-turbo 4.4-liter V-8s, such as the X5 M50i, have bolted to 60 in 3.9 seconds, and our 5742-pound long-term BMW X7 M50i raced to 60 mph in 4.1 seconds. So, we called BMW's press office and asked to retest the M550i. There are plenty of things that can go wrong during testing. Possibly the V-8 or transmission had an issue or maybe the tank was filled a batch of fuel. Whatever the reason, we got a different but identically spec’d M550i back for a retest.

The results of round two were quicker, but still slower than what BMW's claims. Test two resulted in a 3.9-second time to 60 mph and a 12.1-second quarter at 120 mph. Those figures are 0.2-second quicker. The unchanged quarter-mile trap speed, a reliable indicator of a vehicle's power-to-weight ratio, indicates the engine in round two was making the same amount of power as in round one.

Even if this M550i is not as quick as expected, its V-8 remains special. BMW seems to get that and offers the V-8-hungry customer an entire menu section. There are 600- to 617-hp twin-turbo V-8s in M division vehicles (M5, M8, X5M, X6M), and the brand also sells the M550i's engine in the M850i, X5 M50i, X6 M50i, X7 M50i.

Set a mere rung below the M5, the M550i wears a body kit that makes it look nearly as aggressive as the M5, but crammed into the 5-series's engine bay is the detuned version of the BMW's 4.4-liter V-8. An eight-speed automatic is the only transmission, and it works brilliantly, delivering crisp shifts that largely go unnoticed and responding quickly to accelerator inputs. The engine has big lazy power and 553 pound-feet of torque to push you into the 20-way leather seats.

Under keep-the-gas-pedal-pinned acceleration, the M550i is considerably slower than an M5; we clocked the Competition model at 2.6 seconds to 60 and 10.7 seconds through the quarter-mile. But the M550i also is slightly quieter than an M5. The M550i's version of the engine redlines at 6500 rpm to the M5's 7200 rpm, so at full whack the M5 is a touch louder—81 dBa versus 79 dBa. There's a major difference when idling; an M5 registers 50 dBa to the M550i's 40-dBa whisper. The quieter demeanor matches the deluxe interior accommodations. When dressed with a full-leather dashboard ($700) and Cognac Dakota leather seats with the $3400 Bowers & Wilkins audio system playing Mozart's “The Marriage of Figaro,” the M550i xDrive does a convincing Rolls-Royce impression.