Quote:
Originally Posted by swamp2
Footie, there is another effect here. This engine under WOT at redline produces about 250 ft lb. Shifting when getting on it drops the rpm to something like 6000 (of course this varies gear by gear and on gas pedal depression as well). Around that 6k rpm the engine is producing very close it its peak torque, 300 ft lb. Aren't you going to feel a jerk when you try to apply 20 more ft lb over a very short time interval? Unless you make a careful effort to hide it you are going to feel it. You can play tricks with DCT and all sort of parameters as I have mentioned many times in the past like spark, timing, fuel flow, automated throttle control, clutch times and clutch phasing, etc. to control the jerkiness. As long as the jerk is not fake, which I highly doubt it is, I suspect that even with DCT more performance requires more jerk. But in all cases the jerk is less than SMG because there is almost no deceleration. My innacuracy in the past may have been believing that BMW could provide the most performance with little to no jerk. I do think I was wrong about the subtlety myself.
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The jerk is not just from the torque differences at different rpm. Acutally this is only a small part of it. If you shift very fast at 8,300 rpm into the next gear, which needs 6,000 rpm at the current road speed, then there is 2,300 rpm of engien speed which must disappear. This is kinetic engergy from the rotating mass of the engine components and is converted to a surge or jerk or what ever you want to call it if the shift happens quickly.
If you slow the shift down, like I think happens in D1 or D2, then that kinetic energy can dissipate as heat through internal friction of the engine slowing the rpm.