2009 BMW 750i dyno'd, proven under-rated power
2009 BMW 750i – Click above for high-res image gallery
Somehow, we doubt that dyno numbers are quite as important to individuals who are in the market for a new BMW 7 Series as they are to someone shopping for a new Camaro, GT-R or Corvette. As casual observers, though, we'll always be interested to see what happens when a twin-turbo V8 from Bavaria's finest gets a chance to stretch its legs a bit. Fortunately, we're not disappointed with the results.
BMW rates the 4.4-liter twin-turbo V8 at 400 horsepower at 5,500 rpm and 450 pound-feet of torque at 1,800 rpm as it leaves the factory. According to the lucky crew over at Inside Line, BMW's brand-new 750i managed to put down an impressive 391 horsepower at around 5,500 RPM and 434 lb-ft of torque at about 3,500 RPM. Those numbers are at the rear wheels, so drivetrain losses of around 15% must be factored in to find the true power output of the engine itself.
In other words, this engine puts out considerably more ponies than BMW claims. Interestingly, the same is true of BMW's 3.0-liter twin-turbo inline six-cylinder engine. We don't know about you, but this is an error we can forgive.
Gallery: Review: 2009 BMW 750i
[Source: Inside Line]
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Reader Comments (Page 1 of 2)
John Johnson 10:13AM (5/01/2009)
Twin turbo V8 only making 400HP? Wut?
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Aloysius Vampa 10:14AM (5/01/2009)
With 450 lb-ft of torque at 1,800 rpm.
MikeW 11:13AM (5/01/2009)
BMW's twin turbo 4.4 that was used in the '99 Bentley Arnage was only 350hp, but that had a larger cylinder bore & less boost.
DucatiGuy 10:16AM (5/01/2009)
My twin-turbo 3.5L V6 cranks out almost 400 ponies...
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cj 11:09AM (5/01/2009)
No wonder companies overstate their HP, because of idiots like this who think HP means everything... Sigh
Serge 11:10AM (5/01/2009)
Ture... but you wont see any pistons flying through the hood, no leaking heads, no naps while the turbos spool, etc... in general no extra unnecessary stress on any engine component. And it has 450lb-ft torque @ 1800rpm!!!
Ahmet 10:21AM (5/01/2009)
Is it just me or was there a typo? According to the article, the numbers that Inside Line came up with are lower than the BMW figures. What's so impressive about that?
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Seminole 10:29AM (5/01/2009)
The advertised numbers from BMW are what they say the engine makes at the crank. A dyno can only measure horsepower/torque at the wheels. Wheel horsepower is lower than at the crank because of friction loss and whatnot in the drive train that, on average, makes a car lose 15% of its power between the crank and the wheels.
So InsideLine got wheel power numbers almost matching what BMW says the car makes at the crank. Factor in the drive train loss of 15%, and if my math is correct, the engine is making 461HP at the crank.
Rob Roland 10:30AM (5/01/2009)
BMW's numbers are at the crankshaft.
Inside Line's numbers are at the wheels. HUGE difference.
Quote:
"Those numbers are at the rear wheels, so drivetrain losses of around 15% must be factored in to find the true power output of the engine itself."
Seminole 10:33AM (5/01/2009)
I should also clarify that I meant a chassis dyno that measures power through the wheels. You can hook the engine itself up to an engine dyno that will give you the numbers with no drivetrain loss.
For more info, http://en.wikipedia.org/wiki/Dynamometer
Roman Lobkovsky 10:34AM (5/01/2009)
Read the entire post -- the dyno numbers are at the rear wheels, which incurs a drag penalty, which means the numbers at the flywheel are x% higher, where x is anywhere between 10 and 20, depending on specifics.
That being said, it seems quite a few new cars coming out have higher numbers at the wheels than expected given their ratings. Perhaps the engineers have gotten really good at minimizing frictional losses in the drivetrain over the past few years? Maybe the "standard" 10-15% loss for a RWD is too high these days?
Ahmet 10:35AM (5/01/2009)
Thanks for the info Rob and Seminole.
Rob 10:22AM (5/01/2009)
I think it is a stretch to say all 750s are underrated based on testing 1 car.
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MikeW 11:13AM (5/01/2009)
Yes but if the N54 twin turbo inline 6 makes 322hp in the 740i (accurately rated)
then the 4.4 V8, which has a 89mm cylinder bore in lieu of the 84mm bore of the N54, it should have more than 400hp.
Probably 100hp, 50ft-lbs less than the M-ized version
Turall 12:35PM (5/01/2009)
BMW builds engines to very tight manufacturing tolerances. There might be variation of a few horsepower between engines. But if this 750 is pumping out %15 more power than BMW claims, then they all are.
timurjonchik 10:37AM (5/01/2009)
Holly, good news for me.
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jrhmobile 10:37AM (5/01/2009)
BTW, where did Inside Line get that BMW? Was it one someone else bought off the dealer lot, or was it a ringer supplied by the manufacturer for testing?
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Aloysius Vampa 10:44AM (5/01/2009)
BMW provided the car to them. Sometimes they buy them, but more recently manufacturers have been providing cars for them.
Aloysius Vampa 10:45AM (5/01/2009)
Wow. "provided the car to them".
Bodo Albrecht 12:27PM (5/01/2009)
Just to make sure: is everyone applying the same standards? Metric vs. mechanical horsepower? It's only about 1.5% but it would explain part of the difference.
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