Glenn M

In preparation of putting the 89 LSD in my 87 I figured the shift kit would be a good mod, I'm also looking at the dynamic kickdown but haven't seen where it was done in an 88 or older.

I'm looking for shift kit P/N's, and parts sources.

What are the advantages and disadvantages of modifing the torque converter?


This thread from Shocki regarding retrofittiing the dynamic kickdown:

https://rennlist.com/forums/928-forum/245964-dynamic-kickdown-conversion-and-powdercoating-project-finished.html

http://forums.rennlist.com/rennforum...namic+kickdown


From a 90 S4 owner.

I have a 1990 S4 which I would have described as stock until I read this thread and it reminded me I had this mod done in ?1997 - the Porsche dealer mechanics convinced me it was a worthwhile mod, and it certainly was.

I remember it made a stunning difference to the responsiveness of the car, kicking down whenever it was appropriate, into any gear, with sometimes as little as 1cm of pedal travel. I don't remember the last time I put my foot flat to the floor (the classic "static" kickdown) in order to change gears.

To give you an idea of the responsiveness (as one of many possible scenarios) - 30mph in 4th:
- gentle throttle - stays in 4th
- less than half throttle slowly - drops to 3rd
- less than half throttle quickly - drops to 2nd
- more than half throttle quickly - drops to 1st
- will drop to first with a full kickdown at any (rev-reasonable) speed.

Very easy to control and hold gear changes with just throttle position, so you can drive the car more like a manual (though not the same of course). Somebody posted the description of the dynamic kickdown saying it left the car "ready for action" for about 8 seconds - and that's what it feels like - a dynamic sports mode.

About the only negative situation I can think of is when you zip off at the lights in second (standard for the auto) and then realise someone a bit speedy is up with you - just a bit more pressure on the throttle to halfway (where you are wanting to use torque to just stride it out in second) will kickdown into first at 10-15 mph which is a bit embarrassing (makes it look like you are trying harder than you really wanted to). Still, doesn't happen often once you get the hang of the throttle.

All around, I would say it the best GTS retrofit you could consider. Your comment that it allows the 928 to "take better advantage of what's already there" is right on the money. I drive my friend's 1998 SL500 auto, and other late model 3-4 litre engine automatics and notice no difference in automatic control/shifting (and they are 8-10 years newer)

Thanks,
Glenn

V2Rocket

cant you start off the line with an autobox by putting it in the "2" position?

Alan

Schocki has done this on his '92 - I believe it is possible to do on earlier models back to '85 in a basically similar way - however you have to run 1 additional wire to the newer type kick down relay.. Other installation details are as Schocki had detailed.

Mike "byrdman454" is planning to install into an '88 - sometime soon. I have sent Mike suggestion on how I think it needs to be implemented. If that is successful we'll know what it takes. Anything back to an '85 would be a similar install electrically - however the actual effect of Dynamic Kickdown may not be exactly the same - (based on engine & transmission differences).

Alan

IcemanG17

I've been thinking about this mod too......mine will NOT kickdown to 1st at anything over about 20mph....no matter what!! Starts in 2nd......unless about 1/2 throttle then it kicks down to 1st....putting it in "2" and it always starts in 1st and will hold it to at least 5K rpms until it shifts (even under full engine braking).....

It looks like an easy enough mod.....just some wire and a switch...

byrdman454

I am working on it. My 94-95 GTS throttle position switch is on backorder from Germany. I am also in the middle of my intake refresh. They estimated a month to get the TPS, so it will be a couple more weeks. I will take pics for everyone and post it on here. I hope I get this done soon.

Thanks

Alan

Brian - Dynamic Kickdown is rather more involved than a kick-down bypass switch... New kick down relay, new TPS, new wiring...

Alan

IcemanG17

So it takes the kit that Jaeger sells??

John Speake

I have 2 of the required 6 pin throttle switches in stock...

Alan

No that kit is for a fancy parallel kickdown switch - whatever they may call it.

See Shocki's post on this:

https://rennlist.com/forums/showthre...eferrerid=6055

You have to do some DIY for this...

Alan

borland

Without validating the wave shape of the digital speed signal from the 89+ instrument cluster, attempting to install GTS DKD on pre 89' may be a waste of money and time.

Its may be that the digital speed signal is a +12V signal indicating the vehicle speed is 30+mph, rather than pulsed at the same rate as the speedo signal for the speedometer and cruise control.

Alan

Borland - we already went though this in another thread. Its the same pulsed signal that feeds the cruise control brain. Check it out for yourself if you like... look at an '88 cruise with a speed signal - fed from the pulse sender. The same cruise is used in the digi-dash '90+ models where it is fed from the digi-dash sped signal (A): ergo - they both have the same waveform... pulsed to ground. The '94 GTS kick-down relay speed signal (A) is also connected to the same digi dash output - so it seems unlikely it works any differently... In all cases the cruise brain must get the same signal - indication that the waverform didn't change...

I agree for the kick-down relay it would be easier if the dash provided a single level sensitive signal - but it just doesn't. It may well be that a constant low signal will enable the relay (at any speed) but the wave shape is basically a pulse to 0v via the pulse sender or digi-dash output (A) (essentially a square wave based on a pull up).

I see no reason whatsoever that it won't work...

Alan

borland

Alan,

OK I see the GTS wiring is different. Cruise control is from digital A on those cars. So you are right.

For 89' and 90', both cruise control and speedometer get their signal from the PULSE sender.

Speedometer 'A' Digital wiring is the same for 89' and 90', and only feeds to the Kickdown relay.

I just don't understand why they would put the 30mph programming logic in the kickdown relay when they already have a microprocessor in the digital cluster that could do that easily.

Alan

Borland - yes correct - and my explanation was a little wrong (I went round this loop a few times..)

The fact that the same cruise module uses both Speedo A and Pulse sender across model years means they must be the same waveform... so the pulse sender should also be able to feed the later D-K relay for cars without the digi-dash...

I suspect the circuitry in the relay is very simple (dual filter) so it may also be possible to feed it a ground on that pin to make it think 34mph has already been reached... not sure on that (or the practical drivability effects) - Mike may test out that theory during installation

Alan

borland

Alan,

I don’t think fooling the relay about '34mph has already arrived', is going to work.

The earlier kickdown relays hold the upshifts longer based on engine RPM before interrupting the solenoid with the relay.

But for 89’+, there is a special interrupt just for the 1-2 upshift, which makes the shift at a lower engine RPM. In that case, they use the speedometer pulse to determine if 1st gear is engaged.

Here’s the wording from the Porsche guide which explains the earlier, and later (89+) relays.



Here's the relay for the GTS automatic with dynamic kickdown relay. Notice the PIC microprocessor.



Here’s the diagram showing how the hydraulic up shift program is held longer with the kickdown solenoid.



You can see, without the solenoid activated, the hydraulic shift program shifts earlier.

And here’s the corresponding speed/rpm/gear graph.



I opened up the kickdown relay removed from my 90’ S4 during the GTS dynamic kickdown mod. This has the later circuit especially for the 1-2 shift. Here’s a photo of the insides.





There using a couple of identical hybrid boards, each carrying a Philips HEF4538BT. Here’s the datasheet link..

http://www.nxp.com/acrobat_download/...538B_CNV_3.pdf

There are two resistors that were hand soldered in place during assembly, apparently to calibrate the two shift points. Just guessing, it must be using a low-pass filter for the speedo and two high-pass filters for RPM to trigger the upshift hold limits.

For the GTS DKD, here’s the Porsche guide explaination of how it works….



Taking the apart the GTS kickdown relay might find some clues for tricking it with a +34mph signal.
..............
Update

Here's a photo of the inside of the GTS Dynamic Kickdown Relay. Notice the PIC microcontroller.

http://img386.imageshack.us/img386/2...kdrelaygv5.jpg

Alan

Borland - that is good data thanks. sorry I didn't reply before - great post.

Note the dynamic relay diagram in the schematics does not show a correct circuit diagram. As stated here it must act to drop out the solenoid & cause the upshifts at the right RPM point as with the old relay - but it must also power the solenoid for the dynamic kick-down case. The relay diagram shows no means for this to happen on the contacts side.

The 34mph seems to be related to drivability & maybe economy - avoiding wheel spin off the line maybe? The 1-2 kickdown shift at 4950rpm will occur at about 50mph - so not sure there is a relationship to the 34mph detection. I'd assume it would be easy for the dashboard shift signal to activates at different rpm point based on gear selector position? But you may be right - maybe it detects some other speed from the pulse sender for the 1-2 shift.

Since this 34mph limit also existed in the previous version to disable kick down at low speed presumably it most likely still disables both manual & dynamic kick down in much the same way.

Since we know its a pulsed signal - it entirely depends how the speed is determined from this as to what might fool it. Some simple methods could possibly be fooled easily... Not sure if that would just create a major drivability problem though... maybe for off the line starts and 1-2 shift points...

Seems the kick-down relay you opened up has two almost identical boards... I'm wondering if thats 2 differently calibrated speed detection circuits (If so having the dash do all this would seem much easier as you noted).

Alan