2009 BMW 750i: The Dyno Reveals The Beast Within
April 29, 2009
And why not? After all, its 4.4-liter V8 is not only twin-turbocharged and equpped with direct injection, it's been turned inside out. That's right--the intake manifolds are located where the exhaust manifolds usually live, and the turbos nestle in the vee formed by the two cylinder banks.
Does this unconventional layout actually work? Is Nutella a delicious spreadable chocolatey substance? When we finally defeated all of the 750i's numerous electronic protections (including one that throws the transmission into Park if the wheels turn while the door is open), we found out just how angry this flagship luxury liner can be.
Hit the jump for the dyno chart.
BMW rates the 750i at 400 horsepower at 5,500 rpm and 450 pound-feet of torque at 1,800 rpm.
We started our run after 2,000 rpm and found that peak torque arrived a bit later than BMW's claim. Nevertheless, it's safe to say that the engine is, shall we say, robust. What's more, while on the dyno the BMW breezed right up to the rev limiter with little more than a whoosh, as if it wasn't even working hard.
Click the image below for a larger version:
As you can see, there's a big shelf of torque available all the way through the midrange. Torque rolls off steadily past 4,600 rpm followed by a more precipitous drop at 6,500 rpm. Without running all the numbers, it's likely that the BMW turns in its best acceleration times by shifting well short of its 6,700-rpm rev limit.
It's worth noting that turbocharged cars generally produce "high" chassis dyno results relative to normally aspirated cars rated at similar power. Part of the explanation is due to the turbo car's intercooler--automakers tend to heat soak the intercooler to somewhat higher temperatures during their certification process than what you get on a chassis dyno. The result is that the numbers claimed by the automaker end up appearing a bit conservative. And that goes for pretty much any modern turbocharged gasoline engine.
Conservatively rated or no, this sucker's quick. We clocked the 750i at 5.2 seconds to 60 and 13.5 @ 103.7 through the quarter mile. Not bad for a 4,600-lb sedan.
Jason Kavanagh, Engineering Editor