kos11-12

Hi Thilo,
Great stuf !!!
Thanks for sharing the info, I will come back with a few questions if you don't mind, but most of it seams clear , I saw in Colin Belton C4 thread , picture of the modified front shafts.
So do you think we can also keep the original rear shafts (smaller than C2) ?
I was also thinking converting 4th and 5th when at it with shorter ratios, spoke to Mathew at GT Guard transmission & Freinsinger but unfortunately they don't have gears available for the G64 ....

koenig_roland

Hi kos,
i would be glad, to chat with you about "our plan" :-)

I`ll keep the C4 axels. First: because i`ve some sets of rear C4 drive-shafts :-)
and second, because i think it will be sufficient for our cars and my purpose... No slicks, only 17-inch wheels...

Well, about the conversion: i just saw how cheap C2 ABS brains are at ebay. With that in mind, i would prefer to spent some electrican-working hours and make the car think, it is an C2. In the other conversion thread was a solution posted with rewiring the ABS Plug and using the C2 brain.
With that mod, the car is configured like a RS with high pressure brake system, but w/o the hydraulik diff stuff...

About regear:
i hope, with the reduction of power-loss in the gearbox (C2 version ist round about 12 - 15%, C4 version is nearly 30%) and the reduction of wheigt, the car is a little bit more agile..
Shortening the gears with 8/32 would be to short (and to slow on autobahn) for me.

Regards from munich

winter came last night (f*cking snow!)

Thilo

perelet

This topic shows up one in couple of years. Yes people convert c4 to c2. Track people do that. As bonus you get adjustable limited alip diff. Here's example of one of them sold on ebay:

http://forums.pelicanparts.com/porsc...rrera-2-a.html

kos11-12

Hi Thilo , Ok , the C2 ABS is a good idea , I will ring my mechanic as well to discuss and plan the convention
Yep winter is suddenly on us now,
Just living Cannes for Paris, it was sunny but strong freezing wind.

Perelet
Thanks for the info, It's interesting to know the LSD will be adjustable ...will look at it as well .

racoguy

I'm looking at this also but rather than weld anything I'm planning to make a double splined adaptor to lock the two shafts together making it reversible back to stock.

kos11-12

Interesting idea ,
would be best if possible .

NineMeister

To convert 964C4 to C2:

Plan A:
1. Remove front differential & torque tube
2. Remove front drive shafts.
3. Disconnect outer cup of drive shaft and refit to clamp wheel bearing. You can machine this part to reduce weight but it is not essential. If you want to keep your drive shafts intact, buy the 964C2 or RS bolt and ABS ring.
4. Fit gear lever console (support frame) into tunnel, part number 964.501.059.02GRV. To make life easier you can leave the existing top plate in the tunnel, cut the new console to match and weld it on underneath. Done very carefully you can isolate the heat from welding and would not have to strip the interior of the car.
5. Fit complete 964 or 993 or 993RS gearlever assembly.
6. Fit C2 gearbox, either 964 or 993.
7. Fit 964C2 or C2RS rear drive shafts (C4 has smaller joints with smaller load capacity).
8. Plug hydraulic control unit pipes at front and remove lock cylinders.
9. No modification required to ABS.
Benefits: Car now a C2
Negatives: Cost of replacement shafts & gearbox

Plan B:
6. Modify 964C4 gearbox. Remove front differential then lock output shaft to pinion shaft. . Choice is to weld, pin or by making double splined coupling. Seal front output hole.
7. Use stock shafts with limited life.
8. Plug front/rear longitudinal lock cylinder pipe. Retain lateral lock cylinder for active rear differential.
Benefits: Active rear diff
Negatives: C4 gears are heavier, output shaft assembly heavier, overall inertia in gearbox greater than C2. No choice of gear ratios.


To convert 964C4 to use 993C4 transmission
1. Remove 964 gearbox, torque tube, front differential, gear lever
2. Fit 993C4 gearbox, torque tube, front differential, gear lever
3. Manufacture spacers to connect C4 front drive shafts to narrow 993 differential
4. Fit 964C2 or C2RS rear drive shafts
5. Plug hydraulic control unit pipes at front and remove lock cylinders
Benefits: 50kg weight saving, torque sensitive 4wd that eliminates 964C4 understeer trait, option to convert to 2wd for dyno tuning, easy future conversion to permanent 2wd
Negative: Cost of replacement shafts & gearbox


I converted my 964C4 to 993 6 speed C2 and thoroughly enjoyed the different feel and improved performance. I will do the same to my next 964C4 project.

This year we also converted a customer's white 964C4 Targa to a 993C4 transmission (probably the one reported on L9O). The project was a total success and the car drove beautifully with the 993 transmission. This car is the fourth 964C4 which we have converted this way. In the shop at the moment is a 964C4 Celebration (widebody) in silver which is being converted to a 3.8RS specification throughout and ironically one of the previous conversions was also a C4 Celebration, a Viola car that received a full 993TT gearbox and drive train to complement the previously upgraded 500hp turbocharged engine.

I hope this helps.

kos11-12

Hi Colin ,
Thank you for taking the time , great info !!
really appreciate your advise,

The big issue is cost,
By looking at the prices of the gearboxes and parts.....
If money wasn't an issue I would go for a G50/30 with the CAE shifter.

Converting to C4 993, is an interesting option ,
I suppose a few people convert to C2 and sell the parts, But how much the box, torque tube and diff will cost, still , the box may need a rebuild, also I am concern about the G50/20 ratios ...
Could you please explain how does this system works compare to the 964 C4 to keep it permanently to the rear wheels and transfer to the front when loosing grip ?
Where does it loose 50 kg ?

NineMeister

The main weight differences between the 964C4 and 993C4 are:
Torque shaft (964 25mm dia., 993 20mm dia., ~40% lighter)
Torque tube
Front differential
Front drive shafts
Gearbox (964 dual output shaft, one inside other, larger gears; 993 standard C2 box with extension on output shaft only)
Differential (964 full planetary epicyclic diff with actuation; 993 smaller viscous coupling)
Control system (964 ecu, hydraulic valve block, lines, lock cylinders & mechanisms; 993 none)
Add that lot up and you can see where the 50kg comes from.

The 964C4 has a permanent 31/69 percentage split (hence why the rear driveshafts of the C4 have smaller joints than the C2) which contributes to the characteristic 964 push-understeer handling trait. The viscous coupling of the 993C4 normally transmits just 5-15% torque to the front axle making the car very neutral to drive. When the going gets tough (in theory) the system will transmit up to 100% to the front wheels, however the main benefit is that you can push the 993 to oversteer before the front end drive starts to influence the cornering dynamics.

The final bonus is the reduced power losses with the 993 system compared to the 964, in the region of 50% saving between them. More power at the wheels = faster car.

V

Interesting. I thought that putting a 993 C2 6-speed gearbox in a 964 C2 was a straight forward "bolt-on" job, whereas putting a 993 C2 6-speed gearbox in a 964 C4 involves a lot more work to make it fit. Can you please comment on this and also the "different feel and improved performance" as you stated in going from the 964 5-speed to the 993 C2 6-speed gearbox. I'm very curious to hear more about this . I also suppose your 993 C2 gearbox was a ROW box and not US spec?

kos11-12

993 C2 Box is a straight fit to a 964 C2 .
But the conversion of a 964 C4 to a C2 is not that straight forward, still we know a bit more than a few years ago,
as Colin explain; you have 3 options .
Depending on budget and preferences ,
As far as I am concern, if I had over 20k to burn, I would go for a brand new G50/30 with steel synchros and a CAE shifter, in black please.
Unfortunately I am not in that position ....

jack.pe

I've been looking at this as well guys. I dont think that you actually have to do anyhting about the ABS and Electrics. If you just plug up the hydraulics going to the centre diff the PDAS will just think it is still working and the ABS will work as normal. Unless someone knows anything different? the rear diff would then in theory keep operating with the PDAS activating it as normal. What is not clear is if the way it is activated would be beneficial or suited to a 2wd car.
I think I saw someone earlier in the thread mention that it can be converted to be mechanically adjustable from the cabin? how would that actually work?

Something else I am a little worried about is that the C4 gearbox is heavier than the C2 box because of the extra parts. One thing we dont reeally want is a car that is even heavier at the rear than a normal C2. Does anyone know how much heavier roughly it is?

I am working with someone on this and in Jan we are taking a C4 box apart and making plans.

racoguy

You can resistor the electrical connector to the the dual solenoid, I have the resistance value somewhere.

kos11-12

Hi Jack,
According to Perlet post and drawing the master cylinder is replaced with a part that adjust the lsd, can Porsche supply it ...?
not sure either how it can be connected in the cabin with a cable, it would be nice but is it really a must...? Not a big deal to go under the car
to change from road to track setting, time to time.

Concerning the weight difference the C4 box is about 15 kg heavier, by the time we eliminate the planetary gears it will lose most of it,
as Colin said the gears in the C4 box are heavier so the the gearbox is spinning marginally slower than the C2 box , so power would come up slower than with c2 box , Maybe not a big deal in a road/ track car.

Let us know what are your thoughts & plans , thanks

koenig_roland

Back from holidays, i`ll join the topic again.

Thanks for your feedback colin! Nice to read something from you in this topic (and at all in 964 section).

I think, after some thoughts during my vacation, i`ll do it in two (at least) steps. First step would be the pure and simplest way to get rid of the front-drive.

I`ll prefer, to go with C4 ABS unit and leave the hydraulics. Only block/remove the center-diff cylinder with piping and go with an active rear lsd. In my opinion, and if the awd - system works passive, the G64.00 lsd should work as a "normal" mechanical lsd in the OEM 2-WD boxes, if the speed diff between left/right gets more than 6%?! Why should it not work?! i can`t imagine any reason... The only question for me is the overrun situation. Perhaps it works in this condition as an open-diff?!

Focus to (my biggest concern) the shifter. I`ll prefer a plug&play version. So what do you guys think about the CAE component?! Welding/gluing a console to the center-tunnel and fitting the old-school 964 C2 shift assembly to the car, would not satisfy me... I would go with a well know shifter like the wevo/rothsport anyway, so the additional costs for the CAE would be not so big....

An plug&play adaptor for connceting the inner/outer (hollow) shaft together would be the best solution. Does anybody has a picture of the end of both shafts?! I can`t imagine how it could be done... So i came to welding, my mechanic talk about pinning... If somebody fabricates a adaptor, i would be interested.

The weight diff between G50 and G64.00 should be reduced with removing planetary gears like kos said before... If there`s still a disadvantage of 5kg for the G64.00 - i could live with that...

In a second step, i`ll think about doing a sputnik LSD activation, switching to C2 abs brain (or to 996 standalone abs unit)

regards thilo