kos11-12

Hi guys,
The silly question ,
Anyone had experience on converting a C4 box to C2 ,
Also thinking changing 4th and 5th with shorter ratios .

Bill Verburg

If you have a 993 C4, sure no problem

but if you have a 964 C4, no, there's a problem

there are 2 parallel shafts in the transmissions, A transmission gear consists of a set of 2 meshing cogs one on the input shaft and a matching one on the output shaft. The input shaft og g64/00is the same as in other g50s and takes the same gears, the output shaft of the 964 C4 g64 on the other hand is larger(I think 10mm) in OD because it has to have room for the concentrically mounted front output shaft that runs inside it. Since a trans gear is a set of 2 meshing and matching cogs and since there are no 964 G64 output shaft cogs other than factory(AFAIK) you can't change gearing.

This is not the case w/ 993 transmissions where the viscous coupling is attached directly to the front of the output shaft.

You can change gearing where appropriate tooth count g50 cogs are available, I think this to be the case for 3, 4, 5. But they appropriate cogs may or may not be available any longer.

If you want a 2wd you're better off jumping through the hoops to install a g50(there are quite a few of them). Or buying a new car.

kos11-12

Thanks Bill
I kind of guess ...

FormulaRX

How about just enjoying the C4 for what it is? I have a C4 and wonder why anyone would want to change it to a C2...the C4 is great as is and a pretty stout platform

koenig_roland

Hi Kos,
one of the L90 rennlister has just done the G64.00 Conversion. They were some rumors here on rennlist recently.
I`m also quite interested in these informations, because i want to "downgrade" to 2WD too.

But, i`ll stay with my G64.00 gearing. I think, that the reduction of power-dissipation to the 2WD conversion and the reduction in wheigt (~65kg) should be reason enough...

I can`t shorten my gearing, because of german Autobahn-cruising duties... I need a gearing for a proper to-speed... :-)

Let`s wait, what the L90 guys will post about the G64.00 Frankenstein solution.

Regards from Munich

thilo

kos11-12

Hi Thilo,
You mean just use the G 64 and blank the nose, wonder if there is enought support after removing the shaft ....
the box is only 15 kg heavier not such a big deal, and the top 3 gears seams to be well close together,
Plus could be reverted,
I would like to use the CAE shifter....

koenig_roland

Well konstantin,
i don`t know what is done the the box to remove the front stuff... I`be happy to read here on rennlist, what was done on the L90 rennlist members car...

surprise surprise... lets wait and see :-)

regards thilo

kos11-12

Also wonder about the LSD, ABS, and possibility of keeping the smaller C4 rear drive shafts ,

John McM

This may help visualise the G64 box. I'm sure most can Google the French translation..

tdiquattro

Having returned from a 500 mile drive to and from North Wales in conditions that went from dry to storm force winds and rain, flooded roads, standing water and unpredictable grip, then back to high grip dry conditions; all I can say is the C4 is king.

A week long trip round northern Spain earlier in the year proved the amazing grip and drive in fully dry hot conditions.

I regularly drive with C2s and never have trouble keeping up / leading in dry conditions, wet I can make better progress, my engine is stock except for cup and 100 cell cat.

I cannot think of a single reason to give up the superior performance of a well set up lightened C4.

John McM

My experience is the same. I don't notice any performance deficit against C2s on the track in the dry and I have a definite advantage in the wet.

PAOLOP

koenig_roland

Hi kos,
back to your initial question and some remarks from me, after speaking with my mechanic about future upgrades on my blue car.
First: yes, i like the C4. On the ring, it gives my the comfortable feeling i need, to do laps even in the wet. At the redbull ring and the salzburg ring it does not bother me. On fast german autobahn trips, it gives me some safeness in tricky and not complete clear conditions...
But the little child in me is still asking, how much more fun could my blue car (>300 horsepower, quite downstripped, RS suspension) give me, if it were a little bit tail happier (and even 65kg lighter) and does not waste 25 - 27% power in the drivetrain :-)

After the first season with my C2 convertible and some good fun driving kilomteres (5k km this year with the roof open) in the south of france, the customizer in me became total alive and wants to drive 2WD even in the Qpe.

Back to your topic - conversion of a C4 to a C2. In my case, i don`t mind about originality or cars value. It is even a big-boys puzzle and is not that perfect in common sense - but this makes it perfect for me. The target is a reasonable conversion to C2. Buying a G50 or 6-speed G64 box is not an option, because with rising Porsche-values, even the prices of these boxes have exploded.

Target for brainstorming with my mechanic was, keeping my stuff and converting it.

Lets start with the front. The front-driveshafts could be modificated to use the part for the ABS (ABS Ring) and the wheel bearing and the big-nut. I don`t konw its name. Nothing to buy here, just one hour with an lathe (we call it "Drehbank" - i don`t know if the translation is correct).
Front diff can be removed w/o issues. Electric and hydraulic wiring can be modified, but there is no must. I would prefer, leaving the car think, it is still a C4. No C2 ABS brain necessary. So nothing to buy here.
Front trunk and the stuff under the trunk should be doable w/o spending money.

Torque-tube: removing the torque tube is an easy job, but the metall box for the shifting mechanism is missing. My solution here would be an CAE C2 shifter.

http://www.shop.cae-racing.de/index.php?a=158&lang=eng

With this solution, the hole in the C4 tunnel, when removing the Torque-tube, is not an disadvantage - it should be an advantage. I seems to be a pure plug&play job to fit the shifter. Job done. No additional tasks here to prepare the car for it`s live as C2.

First 1200,-€ spent

Now, only the gearbox is still "wrong". My mechanic said, he would leave the G64.00 case as it is. No G50 nose needed. 1/3 of the the box should be empty after the conversion, but with using the orig. box, there is no task for the front gearbox-mounting. Just using the C4 mounting as it is in a C4. I would buy a stiffer one. Just saw one the for the G64.00 with shore 80.

Costs are 100,-€

Inside the box, he would "connect" the hollow shaft assembly (welding and/or pinning) together and remove the whole planetary-assembly in the front of the box. I would let him overhaul the bearings and the synco rings and put it back together. With the hydraulic diff, he recommends a setup, oriented on the C4-Leichtbau, to make the rear diff adjustable. No details here. It could be done electrically, based on the existing stuff, or pure mechnically with an adjustment wheel like the two wheels, the "leichtbau" has.

For the front of the G64, he needs to fabricate a cover to seal it.

The middle diff-lock should blinded down ("blind gelegt" in german).

costs: G64 gearbox overhaul + the mechanical work to welding/pinning the hollow shaft assembly. Lets say 2 - 3k € if your box is just used and not ruined...

So, with round about 4 - 5k€, the frankenstein-conversion could be done and your gearbox should be refreshed within the named money.. Not a to bad deal for a fun-racer... I would spent another money to refresh the rear drive-shafts to finish the drivetrain work for next 50000km :-)

Sorry for my "german" english - but i hope, the opinions behind the process are understandable.

Regards from munich

thilo

hockenheimr

Why not just buy a G50 for a C2 $4,500 and sell your G64 $2,000 (quick sell price), and your net cost would be $2,500 and no tricky trial and error work needed since a lot of shops are doing it.

Axels and clutch probably need to be changed after 25 years anyways.

I don't know what else is needed, but if you need to change the shifter or other parts I am sure you can do a similar buy and sell your old one for a small loss.

koenig_roland

Nobody buys G64 here in europe. Many commercial suppliers offer G64 boxes for small money, but these offers are available for month - nobody needs this stuff.
The other problem is, nobody sells G50 for less than 5k€ here in gemany. G64 6sp. up to 8 - 10k€.

And when buying one, you`ve to rebuild it for being safe for the next years... so another ~2k. At least.

C4 stuff (axels and gearboxes) are crazy cheap and my mechanic has a proper workshop with CNC and the other metalwork toys. He rebuilds the WC engines for modern Porsche up to 4.2l, he`s doing G-Series Conversions up to 3.5l, he`s doing 997 Cup stuff... He drives a 993GT2 factory race car - street legal. Lets conclude he`s positive crazy in porsche things.. in five years i have my porsches there, he had always a proper answer to any question, i asked him and I´ve spent round about 35k€ during this time for rebuilding an anhancing my Qpe and the convertible.

That`s the background.

So he was happy when i asked him, about the situation with gearboxes in times like these, when porsche prices and porsche-part prices increase and increase.
With this thought, we came to the possibilities of using my existing stuff for a 2WD conversion.
He said, that he`s the documentation for the C4 "Leichtbau" drivetrain and he`s thinking about a G64.00 2WD conversion for some month. He also offered me a rebuild of the C4 system, with manual LSDs, like the C4 "Leichtbau" has...

My bullet points are: decrease weight, having a fresh gearbox und going to 2WD. These objectives can be achieved with modifying a G64 box...