Driven: 2012 BMW Z4 sDrive28i
By Tom Martin
August 31, 2011
—Pebble Beach, California
BMW commands a large and impressive engineering group that, over the years, has been responsible for many cars and technologies beloved of automotive buyers and car enthusiasts. But even BMW engineers are not immune to the long reach of the US Environmental Protection Agency. With fuel economy standards for cars rising into the upper-30-mile-per-gallon range by 2016, BMW and other carmakers have begun the long series of introductions that will make that huge (around 40-percent improvement in average economy) change happen.
To that end, BMW invited us to the California coast to drive the new Z4 sDrive28i sports car, which is the first BMW to show off the brand’s new 2.0-liter, turbocharged four-cylinder engine (code named N20). Fortunately, this engine is not only necessary for EPA purposes, but impressive to drive, making this road test worthwhile reading for anyone interested in the kinds of cars you’ll probably own in the near future. The discussion of this engine is also relevant for BMW fans, because it will soon appear in the 5-Series, and then be rolled out anywhere the outgoing normally aspirated N52 six-cylinder engine was used (while the N54 and N55 turbocharged sixes remain in their current applications in the line).
BMW, the self-proclaimed maker of “The Ultimate Driving Machine,” has set some tough standards for the 2.0-liter engine. That’s good because, frankly, a four-banger replacing one of the most revered sixes in history needs some credibility-building. We have our own standards, so we set off down the Pacific Coast Highway, one of our favorite winding roads, to see what this new engine could do.
The N20 impresses immediately, because it has more than adequate torque in the 2000 to 3500 rpm band you’ll run in most of the time. BMW quotes the N20 at 240 horsepower and 260 pound-feet of torque, which, while not mind-blowing, puts its torque spec ahead of the N52 six-cylinder and many other atmospheric engines with more cylinders and displacement. The glory of turbo motors, though, is their ability to generate that torque from very low rpms, and in this case BMW delivers peak torque at just 1500 rpm, along with a wide and flat torque curve that runs all the way up to 5000 rpm. Frankly, the curves for the N20 remind us of diesel engines except that the fun lasts up to much higher rev levels.
On the road, this means that the new 2.0-liter feels spirited and pulls well. We’d say it feels fast, but not super fast or scary fast. Since the Z4 competes with the Boxster, we think those of you who would cross-shop those cars would find them similarly quick. The Z4 feels stronger at lower rpm, and the Boxster might have an advantage up higher (certainly the case in S trim). Compared with Z4’s old six, the new engine feels stronger pretty much across the board, except for the last 2000 rpm before redline.
As we’ve articulated many times, a car’s power level, or even its power-to-weight ratio, is not the most important factor in driving involvement. The shape of the power curve, along with responsiveness and sound, are major contributors to driving fun.
In this case, the new engine in the Z4 delivers power in an admirable fashion that we think is appropriate to the car. Unlike some hyper-kinetic fours, like the one we love in the Mitsubishi Evo, the Z4 delivers its power smoothly and evenly. As you roll into the throttle, you can choose your level of thrust, and the engine will maintain that as revs rise. In contrast some turbo engines feel a little gutless below, say, 3000 rpm, and then come on with a bang. But the Z4 engine is tuned to behave like a non-turbo engine in a lot of ways, except that it feels more powerful than its horsepower spec would indicate.
Those of you accustomed to high-performance turbos will know that the available power band is actually rather narrow, with something like 3000 to 5000 rpm being typical. The Z4 improves on that, with useful punch from 1500 to about 4500 rpm, based on our seat time in the car. What we particularly liked was that the Z4 doesn’t feel a little dull like some supercharged engines, but it also isn’t difficult to drive smoothly, like some turbos. As we said, this balance fits the character of the Z4, which targets a spot that melds GT and sports car traits.
If you are now waiting for the paragraph that says “too bad about the turbo lag,” well, we’re going to disappoint you, because the N20 engine just about doesn’t have any. First off, one part of turbo lag (which broadly is the delay between getting on the throttle and the engine actually delivering power) happens because the torque curve ramps up in the middle rpm range. But in the Z4, the torque is there from the beginning, so that isn’t really a problem. So whenever you get into it, you’re already at peak torque and there’s no “dead spot” to ride out, hence no delay.
The other aspect of turbo lag, which involves delayed throttle response because the turbo impeller has to spin to higher speeds before the power can come, isn’t much of an issue here. Some cars, like the BMW 650i manual we recently drove, have a very short, but still perceptible, pause from throttle application to power delivery. With the Z4’s engine, we’d say that delay is imperceptible. There are engines that have better throttle response than the N20, but if you buy this car, you won’t be constantly reminded by turbo lag that it is a turbocharged car. And, we’d say the throttle response fits the car and most real-world driving quite well.
We’re not out of the woods yet, though, because most four-cylinder engines do not appear on anyone’s list of “Top 10 Best Sounding Engines.” Words we associate with fours include: buzz, drone, nasal, and dull, which isn’t good. BMW, though not usually very extroverted in the sound department, apparently employs a few automotive audiophiles and trotted them out for some serious work on the Z4’s engine. Truthfully, this engine sounds really good, though to get this sonic quality, the engineers had to give it a unique sound rather than mimicking the six-cylinder. The Z4 has a basically baritone mix of exhaust and induction noise, blended with some nice muted mechanical sounds. No thrash, no buzz, but rather a healthy sound indicative of decent power under the hood. It isn’t loud at all, top up or top down, but it certainly isn’t silent either. While the sound is unique in our experience, it sounds a bit like a small-block V-8 with the volume turned down.
Of course, the whole reason to create this new engine is to improve fuel economy. BMW doesn’t have final EPA numbers yet, but from discussions with BMW, we’d estimate a 10- to 15-percent gain over the six being replaced, which should yield something like 33 highway and 22 city miles per gallon. That’s pretty good, considering the enjoyable performance on tap here.
A good engine can be laid low by a bad transmission, but fortunately BMW gives Z4 buyers two high-quality choices. We spent most of our time with the manual, and found it above average in shifter quality, with short throws and good precision. We don’t often say that about BMW manuals, but this Z4 has the transmission we also like on the 1-Series, not the ancient ‘box from the bigger cars.
Also available is an eight-speed automatic. While we’d strongly encourage prospective owners to buy the manual for maximum driving involvement, the automatic is superb for those whose circumstances dictate that choice. The automatic can be paddle- or console-shifted, and this transmission does so about as well as any. The transmission itself is smooth, and the console-mounted shift lever is among the most ergonomic in the business.
So, all-in-all, BMW has delivered a four-cylinder engine that checks pretty much all the boxes. Even though we love many a car built around a four, it is a rarity for such an engine to do so many things so well.
Of course, this is all a giant “so what?” if the whole car doesn’t work coherently. Fortunately, we can make a case that the sDrive28i is the best Z4 on the market. One improvement comes from the lower weight and different weight distribution that the 2.0-liter carries in comparison with the big biturbo six. The result is that the ride is less brittle, and the car simply feels more supple and willing.
The other difference is more philosophical. The turbo four, by being both slower and very exploitable, simply gives you more to play with. You feel the need to use the gearbox a bit more, and you get more extended pleasure from winding the motor out. By contrast, the still-available N54 biturbo six has impressive power, but lives more at the “slam, bam” end of the spectrum. Not that this is bad, and many will insist upon the “speed is everything” model, but as we said, a case can be made for the four-cylinder if you really enjoy the process of driving.
The other benefit of the N20 engine, naturally, is its lower price. At $49,525 including destination charges, the four-cylinder should save you about $5000 over the sDrive35i. That’s not a huge difference, but it doesn’t hurt to save a bit and get such an all-around impressive car. That leaves buyers with the question of whether the Z4 is their kind of car, a question neither we, nor BMW, can answer.
VS: Porsche Boxster
The Boxster is a more involving drive, thanks to more feedback-rich steering and an edge in agility. But the Z4 is certainly fun to drive and, for some buyers, the slight reduction in intensity is probably a step forward. That’s because Z4 is quite good at convertible-style cruising without being lame, flaccid or boring. Neither car is particularly fast, and yet both are fast enough to be interesting to explore and in some ways more fun in the twisties than their big brothers.
VS: Audi TTS
The Z4 feels more fluid, balanced, and involving than the TTS. That is in part because the Z4 is more talkative than the TTS. The Z4 engine has a more interesting sound spectrum and seems less stressed, leaving the more involving car also more able to relax. One benefit is that you don’t have to hammer the Z4 as hard to make things interesting‑a benefit in town and with a passenger in the right seat.
2012 BMW Z4 sDrive28i 6MT
Engine: Inline-4, 2.0 liters, 16v
Output: 240 hp/260 lb-ft
0-60 MPH: 5.5 sec
Fuel Economy, City/Hwy: 22/33 mpg [est]
Base Price: $49,525
On Sale: Winter 2011