The BMW M550i xDrive isn't what we'd call a slowpoke. With its 4.4-liter, TwinPower Turbo V8 engine, it packs quite a meaty punch. The twin-turbo eight-banger puts out 523 horsepower and (390 kilowatts) and 553 pound-feet (750 Newton-meters) of torque. With an engine that puts out even more power than the V10 E60 M5, it's a truly impressive powertrain.
However, Car and Driver wasn't that impressed when they tested the model in its instrumented testing. The 0 to 60 mph claim wasn't met with a time of 4.1 seconds. While it's not what we'd call slow, it's not the sub-4 second time the manufacturer was claiming. The magazine decided to retest the car and loaded it up with higher-octane fuel.
The boosted executive sedan did a little bit better than the initial test. It did the 0 to 60 mph run in 3.9 seconds. Car and Driver noted that it can still do even better given that the much-heaver X5 M Competition can pull practically the same results. The slower than expected acceleration times have caught BMW's attention, and the automaker's solution was to give it an over the air (OTA) update.
So did the software update do the trick for the M550i? The answer is yes, and it's much faster than before. The magazine re-tested the sedan for a third time and finally got the results they were expecting. The 0 to 60 mph time dropped from 3.9 seconds to just 3.5 seconds. It also crossed the quarter-mile in 11.8 seconds at 119 mph (191.5 km/h). That makes it just a few tenths slower than the standard M5.
But what caused the slower runs in the pre-update models? Well, BMW has an explanaition for that. As it turned out, there was a glitch that caused the stability control to interfere. The miscommunication between the engine management unit and stability control module caused the latter to cut power. BMW adds that a similar OTA update is available for the 540i xDrive as well.
Now that all of its 523 horsepower up and running, those considering an M5 should perhaps take the M550i out for a spin first. With a base price of $76,800, it's much more affordable than its more hardcore (and stiffer-riding) stablemate.