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wyovino

Tiptronic - Engine Braking (Downshifting) - Ok or not?

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MY 2000 C2 Tip

I've been searching a few boards and have found that there are two opposing camps on the subject of engine braking.

1 Downshifting a tip to slow down should never be done. It puts unnecessary stress on the engine and transmission.

or

2. Engine braking with a Tip is not a problem. It was designed to do that.

I'm looking for an informed, non-emotional take on this.

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Like everything else, done with caution it should be OK. You can't over rev a Tip( as far as I know) and it will only down shift when it safely can. You might not like the abrupt jerk though when done at high RPM.

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From the Tech Book...

"The Tiptronic Transmission also has the Following Special Functions:

Prevention of thrust upshifting e.g. before curves

If the accelerator pedal is released before a curve, i.e. the throttle is closed quickly, the gear currently being used is retained. If the brake is then actuated, downshifting, appropriate to the current speed, is performed so that the optimum gear is available for the approaching curve.

If the throttle is opened again, shifting occurs according to the shift program.

Gear retention in corners

The current lateral acceleration is calculated from the current driving speed as well as the difference in engine speed. In corners, the respective gear is retained depending on the shift characteristics and lateral acceleration.

Downshifting when braking

If the throttle is closed, downshifting is triggered when the brake is actuated, depending on the speed and the defined braking deceleration. The gear then activated remains engaged until the driver once again depresses the accelerator pedal. This function allows the engine braking effect to be used when braking in curves or when driving downhill. In addition, the correct gear is then already available before the vehicle enters the curve,

Active gear shift skip into SC 5

Whenever the vehicle is started, the transmission control unit has the shift characteristics SC 1. An active gear shift skip into SC 5 can be achieved irrespective of the shift characteristics by quickly opening the throttle. If the throttle is now closed by more than 25%, the previous shift characteristics are resumed.

Kick-down

To achieve optimum acceleration, e.g. when overtaking another vehicle the accelerator pedal must be depressed beyond the full-throttle pressure point (kick-down). The transmission may shift back down to the lowest possible gear, depending on the driving speed. Shifting up to the next gear occurs with higher engine speeds. The kick-down shift speeds remain active until the accelerator has been returned to 70% of its full-throttle position.

Shift-up with overrun on slippery (icy) road surfaces

In overrun conditions, especially in the low gears and on slippery road surfaces, the engine braking effect may cause slippage or locking of the driven wheels. This driving condition is detected by the Tiptronic control unit which continuously compares the speed of the driven rear wheels with the speed of the front wheels. If the speed of the rear wheels is less than that of the front wheels, the Tiptronic system immediately shifts the transmission into a higher gear so that the dangerous driving condition with locking rear wheels cannot occur.

Warm-up map

Apart from the 5 shift characteristics, the control unit also has a warm-up map which becomes active at engine temperatures < 32° C. In the warm-up map, the shift-up points are offset to higher engine speeds, the transmission starts in 1st gear, and the convertor lockup clutch is opened. These measures result in both the engine and catalytic convertor rapidly reaching operating temperature.

Suppression of ignition at gear shift

When gear shifting is performed, the DME control unit briefly suppresses the ignition in order to reduce the engine torque which, in turn, results in smooth shifting."

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Thanks. So if I'm understanding this correctly, in Auto mode, the Tip will automatically downshift when the brake is applied (foot off the gas), depending on the intensity of deceleration. That should mean that manually downshifting in similar situations would be no different than what the transmission would have done on its own. Does this sound right?

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Yes, it's an algorithm that is triggered by applying the brakes. So theoretically you can force it by not applying the brakes and manually downshifting. Hopefully, the control module would prevent any engine over-run conditions.

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We do not have a tiptronic in the 911.

But my wife's Subaru Outback has paddle shifters!??! She uses engine braking often. Sometimes double down shifting. The ECU/TCU matches RPM/Gear so there is no lurch.

I get a kick out of the fact that she does that without even thinking about it but when I downshift in the 911 she gets all "Slow Down! Slow down!" because the engine revs and the FisterD's bark a little.

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Engine braking is possible, but why? It puts additional wear on the transmission. Brakes are cheaper to replace. When you brake, the transmission downshifts under a no load condition. It downshifts so that when you re-engage the transmission (put your foot on the gas) it will be in the correct gear (no engine lobbing).

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I have a 2000 tip, been manually downshifting for over 3 years without problem. Only thing I recall reading is that it is possible to downshift manually and cause an overrev situation - bad. Also read somewhere that under braking in auto mode if you briefly WOT the tip will select the correct gear for the speed. Not tried this.

Going the other way no problem. Launching a tip in manual mode from first to fourth or fifth with wide open will not overrev engine - ecu controls it all for you. Plenty of noise and Gs.

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The tiptronic module will not allow it to shift down if there is a potentail over-rev condition. Double-clicking the buttons will downshift two gears if conditions allow.

Why would anyone say it puts excessive load on an auto transmission, and not with a manual? It doesn't make sense to me. The owners' manual even suggests it for engine braking when going downhill, or slowing for urban areas, etc.

As an aside, the latest PDK has a 'de-coupling' feature for normal driving, which makes the car freewheel when off throttle. It is for economy, but most people seem to dislike the feature. De-coupling is inhibited in sport mode.

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Thanks Richard - its good to know its smart enough not to allow down shift causing over-run. I went back overnight and agree, I found lots of Porsche literature saying its not possible. e.g. From the MY00 owner manual : "Gear changes which would exceed the upper or lower engine-speed limit are not executed by the controller." There is identical statement in the MY03. Now I can stop checking which gear it's in before down shifting and just drive it.

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Loren - is there any description of what type of throttle input causes each of the 5 shift patterns to be chosen?

It doesn't take much experimentation to realize that SC1 is "grandma driving" and SC5 is "WOT, hard". What about in between?

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Loren - is there any description of what type of throttle input causes each of the 5 shift patterns to be chosen?

It doesn't take much experimentation to realize that SC1 is "grandma driving" and SC5 is "WOT, hard". What about in between?

As a Contributing Member you can download and read the tech book here

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Hi Loren. As a new member I'd like to know how to be a ''Contributing Member''... Can you please help..

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