Quote:
Originally Posted by DDS2015
First reason, better gas milage. Second reason, more power.
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I have a lot of experience with turbo-four engines, and my honest opinion is that they are a fool's paradise when it comes down to these two factors.
None of the turbo-fours I have owned over the years have delivered anywhere near their rated MPG in real-world driving, especially under spirited driving. The "throttle tax" is much worse than on larger displacement normally aspirated engines. If you baby them, you can get good MPG. But if driven hard, or driven over a lot of city routes, forget it.
As far as power goes, I own and have owned turbo-four engines that are more powerful than the normally-aspirated straight-six in my Z4. But I would never trade engines with any of those cars. To me, there is a coarseness and lack of refinement in a turbo-four, and it's about 180 degrees from the perfectly balanced and wonderfully smooth straight-six.
Part of what drew me to the Z4 was the legendary BMW straight-six, which has been a nice change of pace from the fours and turbo-fours in my recent sports cars. And that helped justify the price. I probably wouldn't have even looked at the Z4 if it came equipped with a turbo-four. It just wouldn't have been as compelling to me since I have owned turbo-four engines in much cheaper sports cars.
Now, as an example, consider my current SUV, a 2007 Acura RDX. It has a turbo-four rated at 240 HP and 260 ft-lb torque. It's a beast of an engine in terms of power, and based on some recent test drives, it feels a heck of a lot more powerful than the straight-six in the 2011 X3 28i (to be honest, I feel like it gives the 35i a run for the money). But the refinement sucks compared to the X3's engine. In addition to the inherent dynamic characteristics of the inline four cylinder, it's a bit thrashy, the turbo makes the usual cacophony of pumping and whining noises, and the blow-off valve adds an occasional whoosh. It's just not there in terms of refinement.
In terms of mileage, the RDX is rated 22mpg highway, but I can rarely exceed 19mpg on my commute, which is biased to highway driving at 65-75 mph. I drove the X3 28i on the same route, and it got 26mpg, 1mpg better than the window sticker (and on a green car off the lot no less). It confirmed my experience that I can get better mpg with a larger displacement normally aspirated engine that lopes down the highway compared to a frenetic turbo-four that is working fairly hard under the same conditions.
It will be interesting to see if BMW's turbo-four lives up to it's mpg ratings in real-world driving. I don't expect it to, but am open to be proven wrong. As far as refinement goes, however, this is another case where I just wouldn't pay big bucks to get an X3 once it's equipped with the turbo-four. I've been there / done that with turbo-four engines in lower-priced SUVs, and don't see the point of paying the BMW tax for that. Give me the straight-six all the way.