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BMWBLOG Exclusive: Driving the New TwinPower Turbocharged Four Cylinder

Featured Posts, Test Drives | April 12th, 2011 by 26
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Munich, Germany – At one point during Innovation Day, BMW turned the gathered journalists loose to sample the qualities of the new 2.0 L four …

Munich, Germany – At one point during Innovation Day, BMW turned the gathered journalists loose to sample the qualities of the new 2.0 L four in an X1 on local roads and nearby stretches of the Autobahn. The 2.0L four will do duty as the ’28i’ in a number of BMWs and replaces the venerable N52B30.

First, a little praise for the late N52B30. It was an good engine, developed to be naturally aspirated and light. Very light. The cylinder cores are cast aluminum while the surrounding casting is of a magnesium alloy. It was brilliant engineering. It will be retired soon.

BMWBLOG Exclusive: Driving the New TwinPower Turbocharged Four Cylinder

Its replacement has to provide equivalent or better performance, refinement, and smoothness with two fewer cylinders. And an inline four, right out of the box, is not going to be as smooth as an inline six. But, BMW has pulled it off. Balance shafts are a must on four cylinders with volumes significantly larger than 2.0 L, but most 2.0 L fours don’t use them, they aren’t that necessary. But BMW uses a pair of balance shafts on its new four. And that significantly reduces what NVH the 2.0 L four had to begin with.

It’s smooth, and while it doesn’t reach the same peak horsepower of the old inline six, it has more torque (and a much flatter torque curve) and it has more horsepower under 6000 RPM than the six. Where the N52B30 outdoes the new four is in that last 1000 RPM of the engines rev range, 6000 – 7000 RPM. And engines on street cars don’t really spend that much time in the upper rev range.

BMWBLOG Exclusive: Driving the New TwinPower Turbocharged Four Cylinder

The X1 28i we were unleashed on was equipped with a six speed manual and auto stop/start (which I found a bit difficult to get used to – after forty years of driving manual transmissions, this was the first time,
since I owned a Fiat, that the engine died when I took it out of gear at a stop).

The driving showed that BMW has hit its marks with this engine. It has immediate thrust, it is silky smooth at idle, and has a pleasant aural profile, sporty but not overly aggressive. Compared to the six, the four may prove to be more tractable in everyday traffic thanks to the fat, flat torque curve.

BMWBLOG Exclusive: Driving the New TwinPower Turbocharged Four Cylinder

When you look at the numbers, yes the new four has less peak horsepower than the six, but everywhere else it trumps the six. It has more torque (and much more torque earlier in the rev band), it gets better fuel economy (16% better), and is quicker to 100 km/h from a standstill (6.1 seconds versus the six’s 6.8 seconds).

Quite impressive and it bodes well for the other members of the engine family.

Up next, a look at the new 3.0 L diesel. Stay tuned . . .

  • Giom

    I knew this would be a special little engine. How much lighter is it than the 6? Thanks!

    • http://www.facebook.com/profile.php?id=100000477069969 Hugo Becker

      I doubt that it’s much lighter than the N52B30 for a couple of reasons. First the construction of the N52 engine block used a lot of magnesium alloy and it is light in comparison to aluminum. That was possible because the N52 was not designed to use forced induction. The ‘N20′ is a forced induction engine and uses a heavier aluminum engine block. Plus you have all the additional plumbing, intercooler and associated bits that make up the turbocharger assembly.

      It may, however, have less weight in front of the centerline of the axle, which will be good for handling. Look for the next 128i Coupe to be a real gem, especially if they do a full up sports suspension on it. We have no advanced information on that, but I can imagine some engineers are thinking 2002 Tii.

    • http://www.facebook.com/profile.php?id=100000477069969 Hugo Becker

      I doubt that it’s much lighter than the N52B30 for a couple of reasons. First the construction of the N52 engine block used a lot of magnesium alloy and it is light in comparison to aluminum. That was possible because the N52 was not designed to use forced induction. The ‘N20′ is a forced induction engine and uses a heavier aluminum engine block. Plus you have all the additional plumbing, intercooler and associated bits that make up the turbocharger assembly.

      It may, however, have less weight in front of the centerline of the axle, which will be good for handling. Look for the next 128i Coupe to be a real gem, especially if they do a full up sports suspension on it. We have no advanced information on that, but I can imagine some engineers are thinking 2002 Tii.

      • Giom

        Very interesting! I had no idea that you would need a stronger material for forced induction. I have been underestimating the force associated with high compression ratio engins (no Star Wars pun intended:). It puts it all into perspective a little more.

        Thanks for the good explanation!

        • http://www.facebook.com/people/La-Ma/1681833435 La Ma

          it’s not the compression ratio that makes the Turbo needing stronger block. The ratio is just that a ratio between the combustion chamber size and total area.
          The forced induction – turbo or supercharged – puts higher pressure on the pistons and causes them to actually wobble in the block. That force needs stronger side walls. Many times its achieved by thicker side walls, Ford has a current 3.7l V6 engine making around 290HP. They also have a Turbo version but for safety reason they decreased the bore – leaving thicker side walls for the turbo. Size become 3.5L and HP went to 355. This is a very conservative Turbo application. Soon the Mustang will feature the same engine (heard some rumors) and with a 390HP version. 3.5L V6 Turbo.
          BMW’s own 3.0l turbo at 300HP is also not over-boosted at all. They used a relatively small turbo to reduce lag (not completely eliminated) and tuners were able to get 15-20% out of those easy. The N55 TT engine was seeing 400+ HP with Dinan’s magic !
          I suspect the new M3 with the N55 or will it be called S55 ? Twin turbo and size might or may not grow, but I’d bet it will be a 3.2-3.3l TT and HP will be around 425HP It will have to be larger then the N55 as the HP ratings must be higher then the 4.0l V8 it will replace. But again, the sidewall thickness – they need to be sure that there is enough thickness to go with the larger bore. The stroke is usually not enlarged on Turbo engines, but who knows that the //M guys will cook up.
          I know it will be powerful but I know it will have the same issues as all current BMW Turbo engines – high pressure fuel pump issues. They fail fast and in a large numbers. 5 out of 6 guys with a 335i experienced it some more then once already !

          • Giom

            Very insightfull… thanks!

          • Nnnn

            La Ma, that’s very interesting about the wobble, although I’m not sure I understand it. It seems to me that any increase of pressure (compression ratio, forced induction, etc) will result in a proportional increase of wobblin’ force.

            What I’m not sure of is whether this is from the lateral force applied from the connecting rod to the cylinder wall, or the torque applied to the piston because the rod is pushing its lowest point (wrist joint) sideways. Or both, depending on how far down the contact area reaches of the piston against the wall, relative to the wrist joint (and extending that might help both problems).

          • http://twitter.com/atr_hugo Hugo Becker

            The wobble is only around TDC at the end of the exhaust and beginning of intake stroke. BMW provides a very slight wrist pin offset (gudgeon pin for the ‘English’ speakers in the group ;-) to counter this. Think of the piston as pretty much ‘loose’ in the cylinder bore, it uses the flexible piston rings to hold it in place. On throttleless engines (diesels) you’ll get clattter at TDC on the intake stroke, and to an extent you’ll get that also with the Valvetronic equipped gas engines. But on the power stroke, the piston/connectiong rod ‘finds a set’ quickly and doesn’t really contribute that much to clatter.

            In a forced induction engine cylinder pressures are significantly higher than non-forced induction engines. Basically they take in more air and fuel than a similarly sized NA engine. The cylinder head forces on a 2.0L FI engine are significantly greater than a 2.0L NA engine. And it’s one of the reasons that the HPFP is so ‘high pressure’, it has to be able to force fuel into a heavily compressed charge of air.

          • Nnnn

            Oh ok… I thought it was at 90 degrees. So both my theories are wrong. But, I don’t understand in what direction the piston is wobbling and what force is causing it, and what that wrist offset you mention is compensating for.

            Is it that the engine is wobbling against the piston?

          • http://www.facebook.com/profile.php?id=100000477069969 Hugo Becker

            No at top dead center (TDC) in a throttle-less engine (a diesel) and to a lesser extent an engine with variable valve lift (which doesn’t rely on a throttle for most of its operating range) the piston is coming to a halt (it’s at the end of it’s travel in the cylinder) and has a tendency to produce clatter. At idle (basically at low RPM and light loads), a piston with a centered wrist pin can ‘hunt’ (wobble) between the sides of the cylinder wall (remember the piston isn’t a tight fit in the cylinder wall) as it reaches and then travels through top dead center.

            Putting an offset in the wrist pin ‘pre-loads’ the piston to one side of the cylinder. Remember a piston is fixed in place by the connecting rod – it does not rotate in the cylinder (it it did you’d be in a world of hurt ;-).

          • Nnnn

            I didn’t mean that the piston rotated in the cylinder per se, but that the angle within the cylinder could change, which I guess is the wobble you’re describing. Tendency… from what, really? Considering that none of the major forces described would produce an off-center pressure to the piston (in the chamber or via the rod/crank), and the motion of the piston is inherently linear, and presuming zero resistance at the wrist, and presuming no motion of the engine block — I just don’t understand what would cause any wobble. Or, why it would be any more at 0 deg than 90, considering the wiggle-ability offered by the piston rings and gap at any point in its travel.

  • Anonymous
  • Shawn

    Great piece Hugo. I’m excited to sample this engine when it makes its way into the 1 and 3 series. Do you know the engine weight? How does it compare the the NA it replaces?

  • Manny Antunes

    Great article Hugo. We’re all excited to start rolling out product with the new T4.

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  • Sajan

    Yeah you’re right Hugo, i’m glad you picked up on the shortness of the engine there. I own a four pot three series and the front of the engine is just behind the front axle. The fact that it is a shorter engine is a huge benefit to the weight distribution.

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