Isn't it amazing how we all remember exactly where we were when John Lennon got shot? When the whole east coast got shaken with an earthquake and then stirred with a hurricane? And when Volkswagen replaced the EA113 with the EA888?
Good, I've made my point. Betcha didn't even notice that VW replaced the original (EA113) 2.0T with an all-new (EA888) 2.0T. Whatever, it's an engine. Engines come and go. Except that if you're a car fan, you're going to be expected to remember all the details about BMW's newest engine, the N20. And it's a four cylinder. Ennn twenty. Remember this.
BMW may say its middle name translates to "Motor" but we know better: it's actually "straight six" - the engine configuration that the Bavarians have perfected. Let's be honest: the Bee Emm Wizards of the in-line six have never sold a really good mass-market four-cylinder in the U.S. The N20 is replacing the base six in BMW's lineup, starting with the 2012 Z4, so this will prove to be a pivotal moment in the history of BMW.
A four-cylinder in a Bimmer? "This is something we have to wrap our heads around," says Ian Robertson, BMW's sales and marketing director. "The measure of luxury of performance is no longer the number of cylinders and how big each of them is." He's onto something. After all, from only 2.0 liters of displacement, the N20 develops 240 horsepower -- only twenty percent less than BMW's first 5.0-liter V-12.
More importantly, the N20 compares favorably to the "28i" version of the 3.0-liter straight six that it'll replace across the model lineup. That old engine (the N52, if you're taking notes) develops an identical 240 horses - but far less torque. (The straight six makes less than 230 lb-ft everywhere but one teensy spot on the tach; the turbo four twists out all of its 258 lb-ft peak over more than half of its operating range.)
So when it comes to power, cylinder count and displacement are merely two data points; they're no longer the yardstick. But Mr. Robertson also said "luxury," and that is a different matter entirely. The way an engine delivers power determines the character of a car just as significantly as the measure of the power delivered. So while we know that, on paper, a Z4 equipped with the N20 four-cylinder will be faster than the old normally aspirated straight-six (and indeed that was the top-sped "30i" version with 255 hp), the big question on our minds as we walked toward the 2012 BMW Z4 sDrive28i was: what will it feel like?
Well, that and, "wow, this car is still great to look at."
Key comfortably in pocket, we pressed the start button and, um, the Z4 started. There's not a single badge on the car telling of the two missing cylinders under the hood -- just an sDrive28i script on the fender that's inscrutable anyway. And from the sound, you wouldn't know either. While the N20 warms up, the Z4's exhaust note is loud, deep, and angry; exactly as a sports car's should be. The drama wanes a few seconds later as the engine management transitions to a smooth and quiet idle. We put the eight-speed automatic in "D" and engaged the A/C compressor -- typically a recipe for lots of cabin vibration with a four-cylinder. There was practically none, likely the result of two counterrotating balance shafts in the oil pan and a trick flywheel that uses centrifugal force to vary the pendulum length of its counterweights to help reduce vibrations at all engine speeds.
Once underway with the Z4's hardtop up, it's pretty obvious that there's something different underhood. The usual six-cylinder symphony has been replaced with a little four-banger anger -- not in a bad way, mind you, but it's a noticeable change. Under load especially, the N20 takes on a deep and purposeful note that's neither as refined as Volkswagen's benchmark 2.0T four-cylinder's nor quite as angry as a V-8's. The N20 is happiest, acoustically, in the mid range of the tach scale.
And this Z4 is seriously fast. With the eight-speed automatic flinging gears down the driveshaft faster than you can ask "what turbo lag?," the N20 squeezes out enough juice for a 5.6-second run to 60 mph, according to BMW. That's almost a half second quicker than the old six-cylinder and six-speed automatic, and it's enough of an improvement to prevent any regrets about the swap from a naturally aspirated six to turbo four.
We also sampled a Z4 with the six-speed manual. In typical BMW style, the shifter is light and slightly rubbery, with long travel between gates -- and it works beautifully with the clutch to make you look like a smooth-shift hero to your passenger. The N20 is powerful right off idle, thanks to its high compression ratio -- and boost comes on smoothly and almost unnoticeably before the needle hits 2000 rpm. Like the N55 turbo straight-six in the "35i" cars, you could give the N20-powered Z4 to your mom and she wouldn't know it had a turbo on it.
Well, if she was hard of hearing. Whereas some other turbocharged BMW engines are too shy to let turbo sounds out, the Z4 broadcasts them clearly. There's no WRC-inspired blow-off valve chirp, just a pleasant overlay of wooshing and swooshing as you build and release boost pressure. The N20 is redlined at 7000 rpm, but power peaks at 5000 and thrust starts to fall off noticeably after 6000. The automatic is programmed to shift in the mid-6000 range, right about where the tachometer's graduation lines double in density: think of 7000 rpm as the marketing-driven redline, 6500 rpm as the maximum effective engine speed.
The exhaust tuning is perhaps the best part about the Z4 sDrive28i's new engine. This is especially true at low engine speeds with the top lowered. Throttle blips as you engage the clutch to back out of a parking space result in a surprisingly deep bark, though unfortunately that venom is missing with the automatic. Still, the 8-speed is so good that we wouldn't hesitate to recommend it. In fact, it's probably the better match for the N20 overall. (Perish the thought, we know. But the Z4 is more of a cruiser than, say, the hard-edged Porsche Boxster, which just screams for a stick shift.)
BMW says the four cylinder weighs about 22 lb less than the six, but if you look at detailed specifications, it seems the N20's package weighs a couple of pounds more overall -- we're calling it a no-sum game. Since the two front cylinders are gone, there's slightly less weight on the front axle. And by slightly we mean an undetectable 15 lb. There is no real difference in the way the Z4 handles with the four-cylinder.
The difference comes at the pump. BMW predicts the N20 package will give the Z4 a twenty percent boost in fuel economy, which would mean that the previous automatic's EPA ratings of 18/28 mpg would jump to 21/34. We expect the manual transmission's numbers to increase somewhat less than that, especially since the standard stop/start system doesn't make much of a difference in EPA testing.
So how much do entry level Z4 customers save by switching to a four-cylinder? Um, other than the possibility of using less fuel, the new base Z4 is actually more expensive than the old one. Remember, direct injection and a twin-scroll turbocharger cost a lot more than two more pistons: the Z4's base price has increased by $1200 to $49,525. The increased price is offset by additional standard equipment, including Bluetooth and USB audio integration.
The best part about the Z4 is that you can still get a straight six -- either the turbocharged sDrive35i or the fire-breathing, turbocharged sDrive35is. The N20 is easily satisfying enough to stand in for base engine duty here -- in fact, it probably does a better job at balancing performance and fuel economy than the old six did. What it can't solve is the Z4's basic problem: it just costs too much. Half a hundred grand is a lot of money for a roadster, no matter how good it is.
Like the Porsche Boxster and Mercedes SLK, the Z4 is quick off the line but slow to creep out of showrooms. Why? Well, it was designed, conceived, and priced before the world economy tanked. And I bet you remember where you were the day that disaster struck.