Uranium238

I am gathering knowledge and parts together for a rather unusual build that is not really LS related, but not really Porsche related anymore, with zero knowledge from the latter forums.

The project will be removing the Mercedes based 722.3 factory transmission from a 1987 Porsche 928 S4, and swapping in a 4L60E from a C5 Corvette, with torque tube and bellhousing adapted to the factory 5.0 V8 from the car.

Internet searches have revealed some various options on the electronic part while I'm still figuring out the mechanical parts of the swap.

The options are:

1) TCI EZ-TCU adapted to the factory Bosch LH Fuel Injection to read TPS, vehicle speed, and RPM speed.

2) Trans-go Vacuum modulation. I have heard this can allow both automatic and manual shifting. I am not clear on if this covers the installation of a vehicle speed sensor. I'd like to keep my factory speedometer working, so I would need some advice on this.

3) Full manual control through a Trans-go kit.


A couple of things are being considered here:

1) This is not going to be a race car or taken to the strip. It will be a street driven car, but with significantly shorter gearing. I am opting for a 3.90 differential for this setup.

2) I'm not fond of splicing into factory wiring which can introduce electronic gremlins, a plague of Porsche wiring. I like the idea of vacuum modulation but have not heard much on converting a 4L60E to vacuum.

3) If I choose only vacuum modulation, is it possible to hook up a paddle shifter to have manual control over the shifting rather than grabbing the shifter all the time? I have heard of a kit to do this but don't know much about it, not even the manufacturer.

I am open to advice and feedback on this. The question of "why" has been posed to me about this conversion. The answer is simple:

Porsche 928 autos run two types of gearing after 1986: 2.20 and 2.54. While the exact 1-3 gears provide great acceleration to 100, the 4th gear or OD slows the car down as it approaches top speed. On paper, a 3.90 mated to a 4L60E would make a shorter geared monster at the cost of its 165mph top speed, something not attainable without an obscenely priced ticket, suspended license and a trip to the pokey. I am willing to sacrifice top speed, which according to a table I saw, would drop the car down into the high 140s- low 150s depending on engine condition/performance. No biggy.

Next is the BIGGY - ALL and I repeat ALL 4-speed auto 928s after 1985 are prone to thrust bearing failures, which the pressure applied to the flexplate and crank from the torque tube shaft pushes the crankshaft forward into the thrust surfaces. Most 928 owners now release this pressure every oil change by crawling under the car, opening up the lower bell housing and removing the pinch collar bolt that clamps the torque tube to the flexplate, only to Loctite the bolt back in at a higher torque to be redone at the next oil change to stop the movement. Solutions posed are additional clamps, but I figure going the more modern route and chucking the old MB transmission for something with a little more flexibility performance-wise. A 4L60E and C5 torque tube eliminates thrust bearing failures indefinitely due to a better clamping and drivetrain solution.


Thanks for reading!

FTICONVERTERS

iTrader: (3)

Unusual to say the least! What are your plans for a torque converter?

Uranium238

Looking at something for a C5 Vette that has around 2000-2500 stall. Not sure how that would affect the choice of vacuum modulation.

mrvedit

I would enjoy links to threads from others who have made this "crazy" swap. It sure sounds ambitious. I can find links to an entire LS engine swaps, but not to those that keep the 928 engine.

Turbo Trans

This is the closest one I could fine to ask my question. I did a 4l60 swop to 4l80 can I send my pcm off to get changed to the 4l80. I'm having issues finding a tuner that's not 3 weeks out.

murphinator

iTrader: (2)

very cool swap . the 4l60 has an extremely low 1st gear ratio as did its predecessor the 700r4 I don't know that you really need to go as low as 3.90's because of that.

Uranium238

I thought about using the 3.73 ratio but on paper the OD gear is only 6% better than a factory 2.54 rear end.

I have ran into an issue when it comes to electrics. The EZ TCU cannot be used with the Bosch TPS in the 928. The 928's TPS is more of a throttle position switch than sensor. It only tells the ECU when the throttle is wide open, and at idle.

This brings the Microsquirt TCU into the picture which allows the use of a MAP sensor instead of a TPS. However, there is no support for converting the VSS signal to work with my OE VDO speedometer, which accepts square wave signals. In fact the MS TCU harness provides absolutely no output to a speedo whatsoever.

I suppose I could splice wiring into the VSS on the case of the differential, but now what can i use to conver the sine wave signal it puts out to square and get the exact ppm or pulses per mile my speedo needs to function correctly?

mrvedit

First your might want to test if your VDO speedometer will work from a sine wave.
Else it just takes a few cheap components from Radio Shack and a project circuit board to convert from sine to square waves:

http://www.falstad.com/circuit/e-amp-schmitt.html

I couldn't find a ready-to-buy converter, but it might exist.
Google "convert sine wave to square wave".

The MicroSquirt stuff will be much more flexible than the EZ TCU, especially because there is an entire forum devoted to modifing, tweaking and programming it.

murphinator

iTrader: (2)

you didn't say if you already have the 4l60... if not there may be other 4speed od trannys that you wouldn't need a controller for such as the 200-4r or early 700r4 , the 200 is actually easier to make strong and has better gearing , most well known for its results in grand nationals.

Uranium238

I have not purchased the 4L60E yet. What can you tell me about a 700R4? Would a C5 Corvette differential bolt right up to it without any lash adjustments and shimming? Does it fit a C5 torque tube? Is a 700R4 vacuum modulated too?

The transmission is rear mounted on these cars so makeup needs to be very similar.