2011 Infiniti M56: Dyno Tested
May 04, 2011
Having driven our 2011 Infiniti M56 around for several months, one thing is certain -- this big, comfy luxury car has motor. It's an impression we've relayed on several occasions.
Seat of the pants is nice and all, but what sort of powerband does this thing really have? Too often the butt can be fooled by calibration-related tweaks. Is it a top-end screamer or a low-down stump-puller? Such questions keep us up at night.
The dyno has no time for subjectivity or hyperbole. So we did the right thing and strapped our M56 down to the rollers of the Dynojet 248 inertia dyno at MD Automotive in Westminster, CA. The result is, as the kids like to say, after the jump.
The M56 is powered by, aptly, a 5.6-liter DOHC V8 engine. Nissan's being using just such a thing in their Titan and Armada offerings for years.
However, the M56 doesn't use the VK6DE found in those brutes. Instead it employs the newer VK56VD guise, which shares its fundamental architecture (bore spacing, bearing package, etc.) but adds new heads packing direct injection, variable valve lift hardware and a variety of other tweaks.
The core VK engine goes back even further, starting life a decade ago at a piddling 4.5 liters. It's probable that at 5.6 liters the VK is at its limit in terms of displacement.
Nissan's peak ratings for the M56 (as measured at the flywheel, of course) are 420 hp at 6000 rpm and 417 lb-ft at 4400 rpm. Here are its results we measured at the wheels:
The VK56VD clearly favors... well, all engine speeds, really, but it's no slouch down low. There's more than 350 lb-ft of torque to the wheels between 2400 to 5400 rpm and a peak of 377 lb-ft. Power climbs all the way to the 6300-rpm fuel cut where it reaches its peak of 380 hp. Curiously, it didn't reach the 6700 rpm rev limit published in Infiniti's literature. It could be that the M56 has a 130-mph governer, which corresponds to 6300 rpm in fourth gear.
For a luxury car to properly soothe, you don't want some cammy, thumping beast of an engine. Those are great for sporting vehicles but just don't cut it in a luxosedan. You do, however, want torque. Preferably down low, to help muscle a heavy sedan off the line.
In terms of engine design, big cubes inherently deliver big torque (if not, something is very wrong), but also big fuel consumption. That's where direct injection comes in, boosting volumetric efficiency and facilitating a high compression ratio by cooling the intake charge. This in turn results in increased power and improved fuel consumption. Did somebody say 'free lunch'?
You can get a better idea of an engine tuned for a performance car versus a luxury car by comparing the M56's mill to the Ford Mustang 5.0-liter V8 here. Similar in layout (and stroke is nearly identical), the Ford produces exactly the same peak power as the Infiniti, despite being down by 0.6-liter and armed only with conventional port fuel injection.
The Nissan's VK, however, wallops the Ford down low. Note how the torque curves diverge as revs drop. At 2500 rpm the Infiniti generates more than 60 lb-ft more torque than the Ford. What's missing (and what we'll never know) are these engines' BSFC characteristics, or the amount of fuel required to generate a given amount of power as mapped over their entire speed and load range. The fuel-saving benefits of the VK56VD's variable valve lift, high compression and DI would be particularly evident here, particularly at part load.
Makes me wonder what the VK56VD could do were it worked over for performance-car duty. My guess is that it wouldn't take much for this engine to produce supercar-worthy, rock-star high end. Not that there's anything wrong with 380 rwhp. Just fantasizing about a 560Z, I guess.
--Jason Kavanagh, Engineering Editor