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km : First Drive

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9 September 2011

For the last decade or better, Munich, Stuttgart and Ingolstadt have been embroiled in a battle for horsepower supremacy, each taking turns ratcheting up the heat on the others in an unwinnable war of diminishing returns. Like most great escalations, a standdown was inevitable. Just as the Cold War gave way to the realities of the human spirit, the German Horsepower War is being called to a close in response to a new world order that demands less consumption and pollution from that aging but popular instrument of destruction, the internal combustion engine. Of course, the close of one war often opens the door for new ones, and high-strength four-cylinders appear to be the next major front.



This new breed of potent four-pots has been quietly gestating for a few years now, with technology like variable-geometry turbos and direct injection slowly creeping into the mainstream, inhabiting the bodies of traditional sport compacts like the Volkswagen GTI and the Mini Cooper S, among others. However, it’s BMW’s decision to invest heavily in smaller engines that will likely prove to be the first real shot across the bows of competitors, reigniting old tensions in a quest for powerplant superiority. The engine in question is known as the N20, a brimming bundle of techno-goodness that so far pumps out 240 horses from just two liters of displacement. It will likely end up in everything shy of a 6- or 7-series — killing naturally-aspirated six-cylinders along the way — but the first model in America to get it is the Z4 roadster.



The Z4, it turns out, is probably the ideal vehicle in which to launch such an important new engine. After all, there’s history — the Z3 was originally offered as a four-cylinder — and the risk of failure is small, given the modest sales of luxury roadsters in recent years. But as we discovered on the backroads of California’s Central Coast, this new lump is also full of the kind of character that suits a small(-ish) two-seat droptop.



The 2012 BMW Z4 sDrive28i, as it’s formally known, replaces the former Z4 sDrive30i as the anchor in BMW’s US roadster lineup. As such, the basic package is essentially unchanged except for the engine substitution. The 30i’s engine was the highly respected and very modern N52, the 3.0-liter straight-six that paved the way for the current crop of high-tech BMW engines employing such technologies as lightweight bedplate construction, electric coolant pumps, hollow camshafts, direct injection and many others. Output in final Z4 tune was 255 horsepower at 6500 rpm and 220 lb-ft of torque at 6600 rpm.



We’ve already taken a peek at the N20’s internals, so we won’t bore you with the details again, but it’s an infinitely more modern engine than the N52, especially considering there’s just seven years of development between the two. We expect there will emerge various states of performance depending on which vehicle it ends up occupying, but for initial Z4 duty the N20 makes 240 horses at 5000 rpm, and boasts a considerable 260 lb-ft across a span from 1250 to 4800 rpm. What it loses in top-end power it gets back in usable mid-range torque, and then some. Beyond that, BMW claims the boosted four is up to 30 percent more efficient than the old six, at least on the European test cycle (EPA figures are still pending).



Ironically, the new four packs a lot more character than the six it replaces, especially in the sound department. At idle, its high-pressure direct injectors tick perceptibly, doing their best to imitate your average diesel-powered German taxicab. Once the throttle has been pushed, the song changes to an almost boxer-like thrum under modest load in the lower range of the tach. As the revs build past about 4000, the note changes to a more traditional sixteen-valve rasp. Turbo whine is present but well muffled from the cockpit; it’s more noticeable from outside the car, oddly enough. Unlike other turbo two-liters, the N20 never sounds like it’s struggling, just working. Vibration is nonexistent; buzz is not part of the recipe.



Purists will still have the option of shifting their own gears with the standard six-speed, but the efficiency advantages belong to the new eight-speed automatic. Getting to 60 mph takes 5.6 seconds in the automatic, or 5.1 in the manual. Both times represent an improvement over the 30i version, by 0.1 and 0.4 seconds, respectively. Admittedly the manual gearbox is the more emotional choice, and it even incorporates automatic start-stop functionality, but the automatic actually suits the Z4’s easy-going personality better. Even hardcore purists have to admire its quick shifting and perfect rev-matching in sport mode.



What the N20 does best for the Z4 — and will do for every vehicle in which it supplants the old six — is take some weight out of the nose and shift the weight balance slightly toward the rear. In the case of the Z4, it brings almost the entire mass of the engine between the axles, leaving only some ancillary units and intercooler plumbing out front. The result can be felt in nature’s own accelerometer; the car feels a good six inches shorter from the driver’s seat, with quicker response from the front wheels and more predictable tracking through fast corners.



The 2012 Z4 sDrive28i (with a $49,525 including destination base price) will be the first BMW to wear the new N20, arriving in dealers later this month. But it won’t be the only one. The 5-series will get it this fall, and we expect to see it migrate through the majority of the range throughout 2012. And if there’s any doubt that a new battle is brewing, keep in mind Mercedes-Benz will add a 240-horsepower four-cylinder SLK250 to its lineup before year’s end. The armor is on.


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