[bigblackwolf]

The change in engine type on the 28i has been of interest to quite a few people on this forum.
I found a technical publication from BMW and following graph shows the torque and power comparison between the new N20 4cylinder turbo, and the previous 6cylinder natuaral aspirated N52.
Of interest is the torque at low rpm (for non metric units convert 1Nm = 0.738ft lbf).
The N20 has a higher torque than N52 around 1500-200rpm. But the torque of the N20 drops of very sharply below 1250rpm. It is like hitting a brick wall. When driving manual, or automatic in manual mode, you have to take care of keeping rpm a safe distance away from the brick wall.
The N52 torque curve at low rpm is below N20 level, but not so steep. My experience with the N52 is that I can drive comfortably in the 1000-1200rpm range without having the feeling of suddenly losing torque. But on very steep hills, the N52 is lacking torque at 1500rpm, and N20 will be better there.
For the full article (in German), send me a PM private message.

[JoeyO]

Most people read the chart from left to right. But you're reading it from right to left. There's an easy solution to overcome your "brick wall" and that would be to stomp on the gas peddle. Problem solved. And it's not really a problem because the N20 engine is still pumping out higher torque than the N52 engine in that low rpm zone.

If anything, I would consider the "brick wall" for the N20 to be around 5500 rpm. And even that's not bad because most N20 engines will not experience 5500 rpms on an ongoing basis.

[bigblackwolf]

Originally Posted by JoeyO

If anything, I would consider the "brick wall" for the N20 to be around 5500 rpm.

You are right, "brick wall" is not a good term for what I wanted to describe (English is not my first language). "Jumping off a cliff" would have been better.

"Brick wall at 5500rpm": if torque curve drops rapidly with increasing speed, then one can accelerate up to that speed, but not more. If the torque curve is very steep, it is like hitting a brick wall. But at that point, it is a stable system: if speed goes down for any reason, deliverable torque goes up and the car speeds back up to the brick wall speed.

The "jumping off the cliff" is different, as it is an unstable system. Lets imagine following situation, going up a steep hill in manual mode, gas pedal almost floored. If the car slows down for any reason, deliverable torque drops rapidly with the N20, the car slows down more, torque drops even further. It is "jumping off the cliff", you cannot get back up. The only way out is shifting down in gear, but with the N20 you have to do it much faster than with the N52.
All this is relevant only for manual mode. In automatic, the gearbox will assure you stay away from the cliff by keeping up engine speed.

[paul386]

Originally Posted by bigblackwolf

The change in engine type on the 28i has been of interest to quite a few people on this forum.
I found a technical publication from BMW and following graph shows the torque and power comparison between the new N20 4cylinder turbo, and the previous 6cylinder natuaral aspirated N52.
Of interest is the torque at low rpm (for non metric units convert 1Nm = 0.738ft lbf).
The N20 has a higher torque than N52 around 1500-200rpm. But the torque of the N20 drops of very sharply below 1250rpm. It is like hitting a brick wall. When driving manual, or automatic in manual mode, you have to take care of keeping rpm a safe distance away from the brick wall.
The N52 torque curve at low rpm is below N20 level, but not so steep. My experience with the N52 is that I can drive comfortably in the 1000-1200rpm range without having the feeling of suddenly losing torque. But on very steep hills, the N52 is lacking torque at 1500rpm, and N20 will be better there.
For the full article (in German), send me a PM private message.

I don't think you are reading the graph right. BMW probably has limited data under 1250rpm because it isn't particularly useful, it is more difficult to gather the data at this speed, and the engine is more difficult to keep running. Obviously, the engine produces 0 torque at 0 rpm and if their first data point is at 1250RPM you simply connect the dots as an okay approximation. The "steepness" of the curve is a result of the engine producing peak torque so quickly. If they engine didn't product peak torque until 3000rpm you would have a lot less of a drop off and you now wouldn't complain? I think not.

[JoeyO]

The dropoff in torque at 5000 rpm might be a little more noticeable with the N20 than the N52, but I doubt most people would notice a difference. For most of the chart, the N20 torque is higher than the N52 torque (who can complain about that?). And after the N20 torque crosses the N52 torque (at 5500 rpm) it pretty much follows a similar path of the N52 torque, just very slightly below it.

[Aubec]

I think you're totally misunderstanding the graph (Hi, by the way, New here! )

The graph shows a fantastic torque curve, with boost coming in quickly and at low rpm when you mash the gas pedal. This is a curve under wide open throttle conditions and tells you nothing about how the engine behaves at part throttle, or deceleration.

IF you were running uphill, at that low rpm, in such a high gear that torque at the wheels could not maintain your speed then you are not driving properly to begin with. Any car would bog down on a steep hill in too high a gear if your engine speed falls too far below the torque curve - that's why we select a gear appropriate to the hill we're climbing.