Here we go again: a new engine in a new 3-series, and just like last time, the Internet blows up with rumors that the Bavarians have underrated the power output. As always, there's only one way to find out, so we strapped our 2012 BMW 328i onto a DynoJet dynamometer and measured what happened.
Long story short, the 2.0-liter turbo four-cylinder put down 222 hp and 245 lb-ft of torque. [It is rated at 240 hp and 260 lb-ft at the crank.] More important than the peak numbers is, of course, the shape of the curve. And here, the N20 does exactly what we expected: it makes a plateau of torque across the low and middle rpm ranges, and then it tapers off as the turbo's airflow capacity nears.
Are the numbers high? Well yeah -- this is a lot of power for a four-cylinder, especially one with minimal turbo lag. But did BMW underrate this engine at 240 hp? Nah, we don't think so: this number is a little higher than you'd normally expect, but we're guessing that BMW used the 240-hp number as a kind of "worst case scenario" meaning that's the minimum power you can expect in hot conditions.
[For the record, as you can see from the chart below, the N20 puts out 92.5% of peak horsepower to the wheels--similar to both the N54 and N55 six-cylinders. Remember also from our previous dyno articles that we've always published a very conservative result for these engines: early N54s would occasionally put closer to 290 hp to the wheels (and well over 300 lb-ft of torque.) Those engines were a bit stronger than the new single-turbo N55, even though even that engine also put down over 300 lb-ft to the wheels.]
Another interesting engine to compare the N20 to is the normally aspirated straight-six it replaces. In 2007, we took an E85-chassis Z4 3.0si to the dyno. That car used one of the most powerful versions of the N52B30 3.0-liter straight six, rated at 255 hp and 225 lb-ft of torque. (The "28i" version of the N52 was rated at 230 hp and 200 lb-ft. Technically, the N20 replaces this engine, but it's safe to say that the turbo four clobbers that variant in its output.)
The N52 six put down 231 hp, beating the turbo N20 by 9 horsepower. That's well within the noise of the two engine's 15-hp rating spread. The story is similar for peak torque: the Z4 put down 211 lb-ft, or 93.7% of its rated value. The N20's 245 lb-ft dyno result is similar at 94.2%.
We wouldn't use the term "underrated" to describe the N20, just as we wouldn't use the term for the N55, either. We prefer to describe its output as "generous."
More importantly, I've personally spent 2000 miles behind the wheel of the 2012 BMW 328i, and I'm going to quietly take the crown from Volkswagen's EA888 "2.0T" four-cylinder and crown the N20 as the best turbocharged four-cylinder on the market. It clearly makes its advertised horsepower, and I've found that it easily matches its EPA fuel economy numbers. It's smooth, it's quiet, it's responsive, and turbo lag is minimal. Bravo to BMW for an engine that's nothing short of brilliant. As to its qualities as base engine for those non-hardcore buyers who aren't looking for that distinctive straight-six experience, it's definitely underrated.