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      04-15-2011, 11:26 AM   #22
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Drives: X3 xDrive35i w/MSport and +
Join Date: Apr 2011
Location: Quebec

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Originally Posted by Lotus7 View Post
Another interesting feature of the 8HP is its ability to execute shifts under full power very quickly. It’s in the same ballpark as the most sophisticated dual clutch manual transmissions and only transmissions used in much more expensive, very high performance sports and racing cars are significantly faster.

Single gearshift speeds (milliseconds)

Ferrari 575M 250 mS
BMW X3 35i 200 mS
Ferrari F430 150 mS
Ferrari 599GTB 100 mS (fastest shift speed achieved in a production “street’ car)
Ferrari 2010 F1 race car 50 to 60 mS (state of the art)

For reference, a very good driver using a conventional H-pattern manual transmission with good syncros, and a fast-acting manual clutch can perform a manual shift in 500 to 600 mS. A sequential, dog clutch racing manual gearbox might improve that to 300mS.

Finally, the 8HP is one of the few transmissions that can execute downshifts that “skip” going through most intermediate gears. With one shift it can jump from 8th to 2nd. or from 5th to 1st.

For more info about the speed range in each of the (8) gears in an X3, please see this previous thread:
Attached is a pdf with more details about the engineering behind the 8HP transmission.
These numbers are great and agreed this transmission seems fantastic but do you know the power lost compared to a manual transmission? I would be curious too see if the quick shifting compensate for the higher power lost at the wheels during maximum acceleration.