Ultimate C4 AWD Setup?
10-12-2010, 06:54 PM
#1
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Ultimate C4 AWD Setup?
When looking up exactly how the 964 awd system works, it seems to be a very good system, but hampered by the PDAS locking mechanism.
Has anyone tried to eliminate the center diff locker, leaving the split at 31/69 all the time without the understeering problems of the center diff lock, as well as cutting weight. And for the rear diff, has anyone tried to make their own electronic control box to control the lockup on the rear diff? Considering the year it is from, I'm sure it is a fairly simple system compared to nowadays, and I would bet its a PWM controller.
It would seem that if you could do these modifications you would actually have a very nice awd setup. A pure mechanical awd with a 31/69 split is a very very good starting point.
I have searched for threads with this information and have found some but nothing talking about these topics. Thoughts?
Has anyone tried to eliminate the center diff locker, leaving the split at 31/69 all the time without the understeering problems of the center diff lock, as well as cutting weight. And for the rear diff, has anyone tried to make their own electronic control box to control the lockup on the rear diff? Considering the year it is from, I'm sure it is a fairly simple system compared to nowadays, and I would bet its a PWM controller.
It would seem that if you could do these modifications you would actually have a very nice awd setup. A pure mechanical awd with a 31/69 split is a very very good starting point.
I have searched for threads with this information and have found some but nothing talking about these topics. Thoughts?
10-12-2010, 06:58 PM
#2
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If your goal is to try and eliminate the understeer, I might suggest you investigate suspension options. I have a C4 with very neutral handling, through the use of RS Adjustable Swaybars (Front and Rear) with Bilstein HDs and HR Greens.
Check with Steve of Rennsport, as he set me up and it works great. 503 244 0990
Check with Steve of Rennsport, as he set me up and it works great. 503 244 0990
10-12-2010, 07:20 PM
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Yah I know there are ways around it, but I'm a big fan of a good working AWD system. At its core the 964 system is actually very good, but hampered by other things. Just seeing if anyone has played with it or has had the same thoughts.
10-12-2010, 07:25 PM
#6
From what the experts say that bars will fix it up nicely and a C2 is only slight quicker around a track in the most skilled hands for a few laps and then tires start to fall off.
There is vid of a modestly modified C4 that catches up and hangs with an RS. I will try to dig it up.
I guess if you want to call it a problem is the 964 AWD or PDAS is an active system.
There is vid of a modestly modified C4 that catches up and hangs with an RS. I will try to dig it up.
I guess if you want to call it a problem is the 964 AWD or PDAS is an active system.
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10-12-2010, 07:32 PM
#8
Racer
I have no handling problems with my c4 with H&R reds, Koni Sports adjustables, H&R 24F (set soft), 26R (set hard) sways and v aggressive camber. My only issue is that it is about 200Kg too heavy stock and my car is too nice to start stripping.
10-12-2010, 07:35 PM
#9
Mine is bone stock with the ralley car ride height and worn out absorbers and springs and it's nowhere near as bad as everyone was trying to make it out to be. It is only when I really push hard there is noticable understeer in the entry.
10-12-2010, 07:35 PM
#10
I think your idea is an intriguing one. I know from experience that a Subaru STi is more entertaining in the "open" diff setting, which I think is basically what you are getting at. Have you driven your car with the PDAS fuse pulled? Does that leave the clutch pack in a disengaged state?
I am somewhat surprised that no one has tried what you are thinking, especially when one of the many expensive parts in the system fails.
Thinking of the STi gives me another thought, if you have the capability to make a controller for the rear diff, could you make a controller for the center diff, so that you could choose how much clutch engagement you get? My memory is foggy here, but I want to say the STi settings were something like: Automatic, 60%, 40%, and open, or something like that.
I am somewhat surprised that no one has tried what you are thinking, especially when one of the many expensive parts in the system fails.
Thinking of the STi gives me another thought, if you have the capability to make a controller for the rear diff, could you make a controller for the center diff, so that you could choose how much clutch engagement you get? My memory is foggy here, but I want to say the STi settings were something like: Automatic, 60%, 40%, and open, or something like that.
10-12-2010, 07:41 PM
#11
Racer
I've tried with R34 taken out but besides losing ABS didn't improve/change things much at all if u r driving (fast) clean. As Indy said depends on what your goal is. May as well keep a c4 as it is and work on the setup.
10-12-2010, 08:16 PM
#12
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I'm not really just trying to make the car handle, I know that can be done with suspension. It's more of trying new ideas.
I would say the goal is to have a great awd system that gives you the benefits of awd with the handling of a C2.
A lot of people don't actually know how the system works. With no tire spin the system is always on a 31/69 split, which is great actually. It is mechanical and doesnt change. What the PDAS does is when it senses rear tire spin, it locks up the center diff completey for a 50/50 split, which is where the understeer comes from. Unfortunately not adjustable, just on/off switch. Like Tuscany said, if you drive smooth and aren't going 9 or 10/10th, it might not ever engage. But where's the fun in that
The other thing is that the center diff PDAS lock is the weak link. It is known to go out, and in the process can take other things with it. So getting rid of it not only helps handling, but also drops unneeded weight and complexity.
Now the rear diff setup is actually quite strong, coming from the 928 cars which had to handle much more torque. It is a variable lock diff, and is controlled by pressure on clutch packs to determine how much diff lock. Like I said, if you could figure out the electronics, which I'm sure is PWM, you could have a **** to control diff lock from the cockpit.
Another thing would be to trick the PDAS/ABS computer that the center diff was still working, and just let it control the rear diff, but its programming might not be optimal.
I would say the goal is to have a great awd system that gives you the benefits of awd with the handling of a C2.
A lot of people don't actually know how the system works. With no tire spin the system is always on a 31/69 split, which is great actually. It is mechanical and doesnt change. What the PDAS does is when it senses rear tire spin, it locks up the center diff completey for a 50/50 split, which is where the understeer comes from. Unfortunately not adjustable, just on/off switch. Like Tuscany said, if you drive smooth and aren't going 9 or 10/10th, it might not ever engage. But where's the fun in that
The other thing is that the center diff PDAS lock is the weak link. It is known to go out, and in the process can take other things with it. So getting rid of it not only helps handling, but also drops unneeded weight and complexity.
Now the rear diff setup is actually quite strong, coming from the 928 cars which had to handle much more torque. It is a variable lock diff, and is controlled by pressure on clutch packs to determine how much diff lock. Like I said, if you could figure out the electronics, which I'm sure is PWM, you could have a **** to control diff lock from the cockpit.
Another thing would be to trick the PDAS/ABS computer that the center diff was still working, and just let it control the rear diff, but its programming might not be optimal.
10-12-2010, 10:10 PM
#14
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