Andy P.

Been thinking some more since the big thread below on the Tip tranny. I seem to remember someone saying (KjellA I think) that in a Tip equipped A8/S8, the quickest way to pull away from a standing start is to use Tip mode from 1st gear, rather than just Drive. Assuming a European spec shift strategy, surely there would be no difference in shifting (and therefore acceleration) between flooring the loud pedal all the way down with the tranny in Drive, or with it in Tip (allowing the tranny to shift on it's own when the red line is reached)?

Sorry if it's a stupid question, I was bored and tired on the way home from work tonight!! :-)

Andy P.

KjellA

Guess it was me that said it is faster when using tip mode.

Thought just like you do when I first started to wonder about it, so I tried it on track a couple of times. The results actually says it is faster shifting manually.

There might be several reasons for this. I think the main one is that the quickest shift pattern is used when running it manually. Seems like it simply shifts quicker, less hesitation. It probably assumes that when you run manual, you just want to shift the fastest possible way, everything else (like comfort) is less important.

The other thing is the "redline" issue. You will allways (in real life anyway) achieve the greatest total acceleration when shifting beyond the power peak. For most applications, it will give greater total acceleration to keep the engine running as high as possible rather than to upshift at or before the power peak. (don't get confused by the fact that the greatest acceleration is achived at the torque peak, that does only apply for one given gear.)

When running in "D", it will upshift to early. It will start shifting (which it does slower than in "manual" mode) in time such that you never exceed redline. It will actually shift a bit before that. Whan shifting manually, you can let the engine get more rpm before shifting, thus utilizing more power (not peak power, but more than you get by upshifting anyway). Not much, 300-500 rpm. But it means several more german brewery horses down to the ground in every shift.

This, combined whith a quicker gearshift makes it possible to accelerate a bit faster in manual mode. A few of tenths of a second on a 1/4 mile.

Doing this, combined with reving the engine and holding the car back with the brakes at launch will earn you at least 0,5 seconds better 0-60 times than the factory numbers, which are achived from idle and using the "D" program. I have done low 6 secs from 0-62 mph this way.
:-)

KjellA

Realizes that was the wrong term, what I ment was below 6,5 from 0-62. But not a lot, between 6,4 and 6,5 is the numbers I got. So mid 6 would be the correct term I guess.

SteveIAS8

You're right on... to be more specific, the horsepower peak should not be your shift point, nor should your torque peak (as you mentioned).

The reason why the optimal shift points are "beyond" the horsepower peak is because the engine is still developing more horsepower (even though it is at a declining rate) up to a certain RPM past the hp peak than if you were travelling at that same speed in the next gear (where hp is in develping at an increasing rate). Once you reach an RPM where the horsepower for the higher gear is greater than the hp for the lower gear, shift up.

"D" drive will not necessarily shift at that point. As you mentioned, in the A8's case, it may come up short. In alot of other cars, that optimal RPM "shift point" is well below redline, and in automatic mode, these cars, when the pedal is floored, will go to the redline, which is well past the optimal shift point.

Tiptronic is the quicker of the two options. I tried your experiment as well (not on a track, but within speed limits (1st thru 3rd gears only), and the upshifts did feel more crisp as well.

Steve

Basically, shift to the gear at the RPM to keep the horsepower at its maximum