Quote:
Originally Posted by swamp2
A couple of points to add/clarify:
Yes average power is important and it must be considered when trying to understand a vehicles performance. That being said, peak power is still a darn good predictor of overall performance. Also, along those lines, the benefits of more power at rpms which are not seen during WOT contests are irrelevant to the level of performance (basically below 5k rpm in the S55). Should be obvious but it seems to continue to be overlooked.
Also along that line of reasoning keep in mind this tradeoff. Those who prefer engines with an ability to produce a lot of power at low rpm (often sacrificing an ability to do so at high rpm - much like S55 vs. s65) love to talk about the benefit of not having to venture in to "aggressive" driving at high rpm. Well, yes and no. The dyno plots intrinsically assume a WOT condition with boost being pretty well maximized. Thus you can't fully enjoy "lazy driving" at part throttle AND simultaneously enjoy this large gap shown between the power curves.
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Good points. It's no use at a track to have tons more power below 5000rpm, if you allways keep revs above 5000rpm (which I understand is your point as well).
I'd just like to add that when in Sport and Sport+ mode the wastegates are closed during part throttle driving, keeping the turbos spinning (pre tensioned in BMW speak). This means that the engine should feel much more alert and closer to a WOT scenario than it does in Normal mode. I suspect that the S55 will feel much stronger than the S65 even during "non WOT but partial throttle", especially when in Sport and Sport+ mode.
According to BMW the S55 makes 270Nm unboosted (that would be at fairly low load conditions then). The S65 makes a maximum of 400Nm during WOT conditions. The S55 and S65 might not feel all that different during part throttle condition when just running "on the motor" (unboosted).
Where the S65 needed to be tuned (cams, intake runner length etc) for high end power (ususally at the cost of low down torque), the S55 should be able to have been tuned for low end power and torque "on the motor", as boosting provides the power the S65 needed RPM to make.
All the above just my "thinking out loud" thoughts here
