C4 AWD Drivelines

[scootermcrad]

As someone that is really only familiar with building cars that have no exciting electronics, ABS, traction control and are primarily mechanical everything, I'm completely unfamiliar with later cars, but not immune to them and definitely admire how far Porsche has come. I've often wondered about the C4 and it's driveline. If I read correctly, there are some differences between the 964 and 993 drivelines, but I would prefer to ask some questions that are a little more broad.

The engine aside and just focusing on the transaxle, front diff, torque tube assembly, and whatever else is in that driveline, how are these controlled? Do these have their own stand-alone logic system? Are they completely dependent on traction control sensors to distribute power and function or mechanically? Assuming sensors are involved somewhere in the system to detect wheel slippage, is there anyway to control this driveline mechanically or with a simpler control system? Just trying to better understand that driveline.

I'm sure you're asking "what is this person getting at and WHY?" I've always wondered how that C4 driveline would behave in a lightweight early car. Obviously heavy fabrication and adaptation of components is a thing. Especially making room for the components themselves and addressing the AWD uprights and suspension components, but big picture, it seems doable. Yeah, yeah. "Save up and buy a whatever", but not everything is just about going out and buying something. Some of us like to build crazy stuff and think outside the box. So I'm educating myself on just how much lunacy there would be beyond the mechanics of making it all live in the car.

Thanks for any insight and education and for being open minded on the questions. If there's something already out there that better tells the story on these drivelines, I'm all ears. I don't like to waste people's time.

Cheers!

[group911@aol.co]

The good part is that most of the controls are in the components themselves- the transmission and wheels sensors. Take those and all the wiring and that's the bulk.
Then you get into stuff like lateral sensors and ABS computers to make it all work. Anything is possible.
Sold a crashed C-4 to a guy once that put it all under a VW bus.

[Racerbvd]

I have a friend who developed a 964, an engineer, who built a bad ass one with duel LSDs, sadly, dimensionia had set in so can no longer talk to him about the cool stuff that we have discussed for years..
I should have bought his C4 when I had the opportunity.

[scootermcrad]

Originally Posted by group911@aol.co

The good part is that most of the controls are in the components themselves- the transmission and wheels sensors. Take those and all the wiring and that's the bulk.
Then you get into stuff like lateral sensors and ABS computers to make it all work. Anything is possible.
Sold a crashed C-4 to a guy once that put it all under a VW bus.

Thanks for the response! I appreciate it. I’m sure some are rolling their eyes at the idea of using a C4 driveline for anything other than a C4. Was this C4 you speak of an 964 or 993? Later?

Well that sounds promising. I’m going to guess the ABS ties it all together though. That might be the big concern. That adds another layer of complexity. But this is the type of stuff I want to know about. If it could be controlled without adding an entire ABS breaking system, that would be ideal.

[scootermcrad]

Originally Posted by Racerbvd

I have a friend who developed a 964, an engineer, who built a bad ass one with duel LSDs, sadly, dimensionia had set in so can no longer talk to him about the cool stuff that we have discussed for years..
I should have bought his C4 when I had the opportunity.

Sounds like he was a great person to sit and talk with! Thanks for sharing that!

[scootermcrad]

So I guess the above raises the question, does this driveline (964 or 993) have to utilize the car’s ABS system to function? The locker itself seems like it’s single solenoid type control.

Really thinking outside the box, could a front differential from another make be adapted to the torque tube assembly (more fabrication) that wouldn’t require extensive logic, or will the G64 not function properly as a stand alone trans?

[group911@aol.co]

It was 964. For the simplified version, look up C-4 Lightweight.
Not sure if the ABS also played into it but the front rear bias was controlled by knobs on the dash.
Some C-4's also had LSD in the rear so between that and manual front bias control, you might be able to balance it out.
993 used a different slip coupler for the front.
Hopefully Bill Verberg will chime in. He understands these way more.
BTW, C-4's are a blast on the track. The answer for everything is more throttle

[scootermcrad]

Originally Posted by group911@aol.co

It was 964. For the simplified version, look up C-4 Lightweight.
Not sure if the ABS also played into it but the front rear bias was controlled by knobs on the dash.
Some C-4's also had LSD in the rear so between that and manual front bias control, you might be able to balance it out.
993 used a different slip coupler for the front.
Hopefully Bill Verberg will chime in. He understands these way more.
BTW, C-4's are a blast on the track. The answer for everything is more throttle

Oh man! I like the sound of all that! Thanks! And hopefully Bill will have some insight.

[Bill Verburg]

Originally Posted by scootermcrad

As someone that is really only familiar with building cars that have no exciting electronics, ABS, traction control and are primarily mechanical everything, I'm completely unfamiliar with later cars, but not immune to them and definitely admire how far Porsche has come. I've often wondered about the C4 and it's driveline. If I read correctly, there are some differences between the 964 and 993 drivelines, but I would prefer to ask some questions that are a little more broad.

The engine aside and just focusing on the transaxle, front diff, torque tube assembly, and whatever else is in that driveline, how are these controlled? Do these have their own stand-alone logic system? Are they completely dependent on traction control sensors to distribute power and function or mechanically? Assuming sensors are involved somewhere in the system to detect wheel slippage, is there anyway to control this driveline mechanically or with a simpler control system? Just trying to better understand that driveline.

I'm sure you're asking "what is this person getting at and WHY?" I've always wondered how that C4 driveline would behave in a lightweight early car. Obviously heavy fabrication and adaptation of components is a thing. Especially making room for the components themselves and addressing the AWD uprights and suspension components, but big picture, it seems doable. Yeah, yeah. "Save up and buy a whatever", but not everything is just about going out and buying something. Some of us like to build crazy stuff and think outside the box. So I'm educating myself on just how much lunacy there would be beyond the mechanics of making it all live in the car.

Thanks for any insight and education and for being open minded on the questions. If there's something already out there that better tells the story on these drivelines, I'm all ears. I don't like to waste people's time.

Cheers!

awd used in a 964 is a completely different animal compared to awd used in a 993

964 awd is all hydraulically controlled w/ both transverse and longitudinal clutch packs that provide varying lockups depending on signals from lateral and longitudinal sensors located in the console between the seats

Here's the heart of the 964AWD
1 & 2 are concentric output shafts, 1 is the output to the regular CWP assembly which has a transverse clutch pack regulated by variable hyd. pressure, instead of the more usual spring /ramp tensioned LSD



parts in green are std G50, the rest is 964C$ specials


Power flow green is the drive input from the engine, red is engine speed w/ selected gear ratio, yellow 31% front drive, blue 69% rear wheel drive drive % are controlled hydraulically

longitudinal clutch pack
red engine speed w/ selected gear ratio applied yellow 31% fwd blue 69% rwd


964awd transverse differential(AKA space age lsd)

[Bill Verburg]

993 AWD on the other hand uses a std g50 w/ a viscous lsd mechanism attached to the front of the output shaft, no external control inputs are used, just the viscous fluid temp change induced variable lockup

9993 g50 rwd


993g64 awd


viscous long. lsd





964g64 awd


viscous clutch mechanism

unlike the 964 awd, the 993 can easily be converted to rwd by removing the viscous mech. and replacing the front cover w/ the rwd part

[Matt Monson]

The 993 installation would be waaayyy easier, though Singer is snatching up a bunch of them and using them in their builds for reliability’s sake.

To me the greatest obstacle would be the AWD stuff in the front end. You would almost have to weld in a 964 C4 front cut to get the clearance and mounting points for everything.

[scootermcrad]

Originally Posted by Bill Verburg

993 AWD on the other hand uses a std g50 w/ a viscous lsd mechanism attached to the front of the output shaft, no external control inputs are used, just the viscous fluid temp change induced variable lockup

Wow wow!! Thank you Bill!! Tons of incredible information!!! I honestly expected the 964 installation to be the simpler solution, but it sounds like the 993 is pretty self-contained and simple. Or am I missing the point?

I could make room for either arrangement. The G64 trans looks significantly longer compared to the later G50. That’s certainly a plus.

So what would need to be scavenged from a donor vehicle to control this, besides the mechanical components themselves?

Sounds like if 964 C4 components were used, a lot of hydraulic components would have to be obtained.

[Bill Verburg]

Originally Posted by scootermcrad

Wow wow!! Thank you Bill!! Tons of incredible information!!! I honestly expected the 964 installation to be the simpler solution, but it sounds like the 993 is pretty self-contained and simple. Or am I missing the point?

I could make room for either arrangement. The G64 trans looks significantly longer compared to the later G50. That’s certainly a plus.

So what would need to be scavenged from a donor vehicle to control this, besides the mechanical components themselves?

Sounds like if 964 C4 components were used, a lot of hydraulic components would have to be obtained.

No, only the 993 version is self contained,

as I stated the 964 version is controlled by 2 expensive accelerometers located in the cabin console between the seats, the hydraulics are also tied into the brake system hydraulics and the also very expensive external hyd. pressurization system

[scootermcrad]

Originally Posted by Matt Monson

The 993 installation would be waaayyy easier, though Singer is snatching up a bunch of them and using them in their builds for reliability’s sake.

To me the greatest obstacle would be the AWD stuff in the front end. You would almost have to weld in a 964 C4 front cut to get the clearance and mounting points for everything.

Oh man! Leave it to Singer to kill the parts market on this stuff. That will drive up prices quite a bit. Errr!

And for the front diff, it certainly would take some fun fabrication. If a donor vehicle would be used for parts shopping, front geometry will have to be studied pretty carefully, or maybe even grabbing an entire front clip to replicate the geometry and fabricate a custom pan and tank support to mount it all correctly. I would also have to consider a custom fuel tank, I bet. None of that is a deal breaker, in my mind.

Thanks for your input! Glad you mentioned the Singer situation!

[scootermcrad]

Originally Posted by Bill Verburg

No, only the 993 version is self contained,

as I stated the 964 version is controlled by 2 expensive accelerometers located in the cabin console between the seats, the hydraulics are also tied into the brake system hydraulics and the also very expensive external hyd. pressurization system

Ok! Thank your for the clarification. Seems like a no-brainer, compared to the 964 arrangement. Great information! Thank you!!

[group911@aol.co]

The 964 inner front is going to easier to use than the 993. The 993 is actually a lot different in many dimensions as far as the body work goes. I think the suspension mounting points are going to be the same 964 to 993. You'll need to replace your tunnel and either 964 or 993 are close to each other. You'll also have to use the 993 torque tube if you are going that route as they are completely different than 993.

Originally Posted by scootermcrad

Oh man! Leave it to Singer to kill the parts market on this stuff. That will drive up prices quite a bit. Errr!

And for the front diff, it certainly would take some fun fabrication. If a donor vehicle would be used for parts shopping, front geometry will have to be studied pretty carefully, or maybe even grabbing an entire front clip to replicate the geometry and fabricate a custom pan and tank support to mount it all correctly. I would also have to consider a custom fuel tank, I bet. None of that is a deal breaker, in my mind.

Thanks for your input! Glad you mentioned the Singer situation!

[Matt Monson]

Originally Posted by group911@aol.co

The 964 inner front is going to easier to use than the 993. The 993 is actually a lot different in many dimensions as far as the body work goes. I think the suspension mounting points are going to be the same 964 to 993. You'll need to replace your tunnel and either 964 or 993 are close to each other. You'll also have to use the 993 torque tube if you are going that route as they are completely different than 993.

Yes. I suggested 964 clip because it’s basically still G body. Like you mentioned, 993 was all new.

I don’t think it’s been mentioned, but the reason the 964 stuff is so complex is because it’s 959 based. They were trying to use up parts and capitalize on all the engineering that had gone into that car. Great for performance but overly expensive and complicated long term. The 993 system has served them well, being the basis for 993 C4, 993 TT, and 996 TT.

[scootermcrad]

Originally Posted by group911@aol.co

The 964 inner front is going to easier to use than the 993. The 993 is actually a lot different in many dimensions as far as the body work goes. I think the suspension mounting points are going to be the same 964 to 993. You'll need to replace your tunnel and either 964 or 993 are close to each other. You'll also have to use the 993 torque tube if you are going that route as they are completely different than 993.

OH! That’s a great point! Lots of differences up front!

If one were to acquire an entire 964 front clip with suspension, would there be any issues with using 964 half shafts/CV’s on the 993 front diff? Most likely, I will be making a set of 935 style LCA’s for this car (RWD or AWD). So I would have questions about suspension geometry, if I go down this road, but could build the track width to accommodate whatever is needed, I suppose.

[scootermcrad]

Originally Posted by Matt Monson

Yes. I s
I don’t think it’s been mentioned, but the reason the 964 stuff is so complex is because it’s 959 based. They were trying to use up parts and capitalize on all the engineering that had gone into that car. Great for performance but overly expensive and complicated long term. The 993 system has served them well, being the basis for 993 C4, 993 TT, and 996 TT.

Yep! That makes total sense!

If sourcing 993 C4 components becomes an issue, due to increased demand, I would have to consider the 964’s complicated system and maybe figure out control of the hydraulics another way, if that’s even a remote possibility.

Or, just be a normal human and just stick with a RWD 915 trans. Haha

[group911@aol.co]

I think the geometry will be the same. Bill will probably have the answer on the halfshafts and CV compatibility.
On using the 964 with manual controls, it seems like the c4 lightweight system might be mostly manual. Not sure where you could find out how their systems worked.
https://www.youtube.com/watch?v=lkKEuaue_fA
If you can believe an auction house description;
"Developed following Porsche’s experience with the 959, the Carrera 4 used a four-wheel drive system with electro-hydraulic control of the transfer case clutches. Lateral load, speed and acceleration sensors work with the electronic brain to maximize its performance. In the C4 Lightweight two switches give the driver the ability to tailor both the front-rear and lateral torque split of the transfer case and rear differential. Widely held to be superior in performance, but less highway friendly, than its successor system on the 993-series, the 964 Carrera 4 made the perfect basis for a loose-surface competition car."
https://www.bonhams.com/auctions/18267/lot/232/?category=list