2012 BMW 328i: Dyno Tested

BMW is making haste in relegating its normally aspirated inline-six to the dustbin of history. First it was the 528i and Z4 SDrive28i, and now the 2012 BMW 328i has made the transition to a 2.0-liter boosted and direct-injected four-pot known in BMWland as N20.

And it's not like this all-new 3 Series is a smaller car than its straight-six-havin' predecessor. In fact, the 2012 328i casts a larger shadow and weighs just a hair more than the outgoing car. Yet the N20 moves the 328i with ease, perhaps with more ease than its rated values of 240 horsepower and 255 lb-ft of torque suggest. 

With that, off to MD Automotive 's dyno rollers we go.

You'll notice that the devastatingly handsome speaker in the video said that the 2012 328i's factory rating is 245 horsepower. It is, if you believe the owner's manual, which is where I he found that number. 

A brief conversation with BMW afterwards revealed that the numbers in the owner's manual are not correct and that the real rating is indeed 240 horsepower (and 255 lb-ft of torque).

According to our dyno testing, neither set of numbers are correct -- they're all conservative. See here:

That's 240 horsepower and 257 lb-ft of torque as measured at the wheels. It was dead-repeatable on the dyno, too, laying down the same power over nine consecutive pulls.

Like observed with the Z4, there's a dip in the 328i's torque curve at 5300 rpm, less pronounced in the 328i but still present. Also, that hole at 2300 rpm showed up in every pull and I even felt it on the road. It's so low in the rev range, though, that you really have to drive like a clown to elicit it.

And like always, our testing was on 91 octane "premium" fuel. Yes, that's the best we can get in California. Yes, it's lame. 

Now, we've previously dynoed the N20-equipped Z4 SDrive28i, rated at a near-identical 240 horsepower and 260 lb-ft of torque. And we found it to be similarly stout, producing nearly as much power as measured at the wheels as is claimed at the flywheel. 

The 328i eked out a thin whisker more urge across most of the rev range, but you can probably chalk the difference up to run-to-run and car-to-car (and day-to-day) variation:

Same roll-off of torque at 5000 rpm, same end to the festivities 7000 rpm. The N20 is not an engine that begs to live near the rev limit, but it does generate a fat slug of torque that makes daily driving easier. 

And in the 328i, this power delivery makes sense. Less so in the Z4. Sports cars are not sedans, and the engine's character should reflect this. 

Another thing you'll notice in the video -- power and torque gauges on the 328i's multimedia screen. I stumbled across the display while poking around iDrive between pulls. 

The gauges are in metric, but when you convert the peak numbers, it says it produced 228 horsepower and 251 lb-ft of torque. Not too far off of what we measured at the wheels during that run, actually. The display is a gimmick, but at least it's a somewhat accurate one.

Anyway, yeah, the N20 continues to be strong. I don't think anyone's going to complain about that. The low-gain throttle pedal, maybe. But not the grunt it puts out.