c4 awd specifics anyone?
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From: dc
c4 awd specifics anyone?
hello
i'm trying to determine whether the c4/c4s has a limited slip differential up front or not. i'm aware of the ABD in the rear, and the center being a VC unit. any experts wanna help me out?
i'm trying to determine whether the c4/c4s has a limited slip differential up front or not. i'm aware of the ABD in the rear, and the center being a VC unit. any experts wanna help me out?
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See the following archived website:
<a href="http://web.archive.org/web/19970129181653/www.porsche.com/DrM.htmlhttp://" target="_blank">Porsche.com 1997 Models and Specs</a>
You will see if you check the Carrera 4 and the 4S that they both save LSD in the drivetrain. I believe that this is in the rear axle only.
<a href="http://web.archive.org/web/19970129181653/www.porsche.com/DrM.htmlhttp://" target="_blank">Porsche.com 1997 Models and Specs</a>
You will see if you check the Carrera 4 and the 4S that they both save LSD in the drivetrain. I believe that this is in the rear axle only.
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If you look at the url that Fred's link provides, you just need to delete the http:// off the end. Try this:
<a href="http://web.archive.org/web/19980114103509/www.porsche.com/DrM.html" target="_blank">Try This</a>
Skip
<a href="http://web.archive.org/web/19980114103509/www.porsche.com/DrM.html" target="_blank">Try This</a>
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Here's a link from this week with a lot of good information.
<a href="http://autozine.kyul.net/911/911_9.htm#4wd" target="_blank">Carrera 4 Wheel Drive Explanation</a>
If you want to see the whole site, you'll need to strip the URL to the base.
<a href="http://autozine.kyul.net/911/911_9.htm#4wd" target="_blank">Carrera 4 Wheel Drive Explanation</a>
If you want to see the whole site, you'll need to strip the URL to the base.
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From: Back In RI...............
"993’s system
Left: 993's 4-wheel drive system; Right: a typical viscous-coupling differenital
In contrast to the 964, the 993’s 4-wheel drive system was rather conventional and simple, but it actually performed far superior in real world. Instead of epicyclic differential and mult-plate clutch, it used a simple viscous-coupling LSD as centre differential. To most FF car, viscous-coupling means understeer, but for the rear-wheel-drive-based 911, it means very much loyal to the Carrera 2’s character yet provided superior grip when needed.
To make the viscous-coupling always engaged the front wheels, the rear tyres were made marginally smaller in diameter, enhance established a small speed difference between the drive shafts to front and rear. With the speed difference, the viscous liquid normally transferred 5-15% torque to the front axle, which was much less than the 964’s system. In abnormal conditions, that is, whenever one axle lost grip, the viscous-coupling LSD may send up to almost 100% torque to the other axle.
Both the center LSD and rear LSD were now pure mechanical, but clever electronics was used in the newly-added ABD (Automatic Brake Differential). Again, ABD was simple yet effective. It was just a program, sharing all the hardware with ABS. Whenever rear wheels spin, it braked the spinning wheel thus the rear differential would send more torque to the other wheel. It was particularly useful for extreme conditions such as on snow, while LSD covered most normal conditions."
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Left: 993's 4-wheel drive system; Right: a typical viscous-coupling differenital
In contrast to the 964, the 993’s 4-wheel drive system was rather conventional and simple, but it actually performed far superior in real world. Instead of epicyclic differential and mult-plate clutch, it used a simple viscous-coupling LSD as centre differential. To most FF car, viscous-coupling means understeer, but for the rear-wheel-drive-based 911, it means very much loyal to the Carrera 2’s character yet provided superior grip when needed.
To make the viscous-coupling always engaged the front wheels, the rear tyres were made marginally smaller in diameter, enhance established a small speed difference between the drive shafts to front and rear. With the speed difference, the viscous liquid normally transferred 5-15% torque to the front axle, which was much less than the 964’s system. In abnormal conditions, that is, whenever one axle lost grip, the viscous-coupling LSD may send up to almost 100% torque to the other axle.
Both the center LSD and rear LSD were now pure mechanical, but clever electronics was used in the newly-added ABD (Automatic Brake Differential). Again, ABD was simple yet effective. It was just a program, sharing all the hardware with ABS. Whenever rear wheels spin, it braked the spinning wheel thus the rear differential would send more torque to the other wheel. It was particularly useful for extreme conditions such as on snow, while LSD covered most normal conditions."
Is this what you are looking for?
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From: Nor Cal
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Phil McGrath:
<strong>the rear tyres were made marginally smaller in diameter, enhance established a small speed difference between the drive shafts to front and rear.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Awesome info, Phil. That would make sense why the diameters of the stock C4S/TT tires at 225/40/18 and 285/30/18 are different.
Here are the diameters:
225/40/18: 25.09 in
285/30/18: 24.73 in
In previous posts about using different tire sizes, other have suggested keeping the ratio very close to each other to reduce wear on the visous coupling.
However, it seems that the ratios must not only be similar, but favored toward a smaller diameter rear as well.
Thanks, it makes sense now.
<strong>the rear tyres were made marginally smaller in diameter, enhance established a small speed difference between the drive shafts to front and rear.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Awesome info, Phil. That would make sense why the diameters of the stock C4S/TT tires at 225/40/18 and 285/30/18 are different.
Here are the diameters:
225/40/18: 25.09 in
285/30/18: 24.73 in
In previous posts about using different tire sizes, other have suggested keeping the ratio very close to each other to reduce wear on the visous coupling.
However, it seems that the ratios must not only be similar, but favored toward a smaller diameter rear as well.
Thanks, it makes sense now.
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From: dc
Phil,
i'm aware of the center viscous differential, as well as the rear limited slip differential. However, there is a differential at the front of the car as well. i'm wondering if the front differential is also a limited-slip differential, as in the rear and the center.
Jeff,
typically a margin of difference no greater than 5% - 7% in shaft speed (front to rear) is recommended in viscous coupling type all wheel drive systems, so as not to burn the differential out.
i'm aware of the center viscous differential, as well as the rear limited slip differential. However, there is a differential at the front of the car as well. i'm wondering if the front differential is also a limited-slip differential, as in the rear and the center.
Jeff,
typically a margin of difference no greater than 5% - 7% in shaft speed (front to rear) is recommended in viscous coupling type all wheel drive systems, so as not to burn the differential out.
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I'm wondering what the differences with the new 996 AWD systems are that allow a 295 rear tire to be used instead of the 285 size rear tire (as in the 993-based AWD systems).
The 295 size tires are much closer in circumference to the 225 front circumferences. Therefore the differences are much less in speed between the front and rear tires and less torque is moving up front. The 996 gearing must be making up the difference somehow.
*****
The 295 size tires are much closer in circumference to the 225 front circumferences. Therefore the differences are much less in speed between the front and rear tires and less torque is moving up front. The 996 gearing must be making up the difference somehow.
*****
Burning Brakes
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Back to original question.
993 4S has LSD and ABD in the back, when ordered. Instead of center differential 994 4S employs VC. It is physically located in the front differential but front differential itself is not lockable. Porsche put VS in front because of lack of space with tipronic gearbox.
VC - silicon viscous coupling
LSD - Limited slip diff
ABD - automatic brake differential
993 4S has LSD and ABD in the back, when ordered. Instead of center differential 994 4S employs VC. It is physically located in the front differential but front differential itself is not lockable. Porsche put VS in front because of lack of space with tipronic gearbox.
VC - silicon viscous coupling
LSD - Limited slip diff
ABD - automatic brake differential
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</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Jack Ennuste:
<strong>Porsche put VS in front because of lack of space with tipronic gearbox.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Somehow, I am missing the relationship between the VS (Viscous Coupling) and Tiptronic since the AWD versions of the 993 were not available with the auto box. Care to clarify?
<strong>Porsche put VS in front because of lack of space with tipronic gearbox.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Somehow, I am missing the relationship between the VS (Viscous Coupling) and Tiptronic since the AWD versions of the 993 were not available with the auto box. Care to clarify?
Burning Brakes
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</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> Viken: AWD versions of the 993 were not available with the auto box </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Yes, Viken. There are no 993 4S or 993 TT with tiptronic. It happened with 993 -> 996 evolution. My source is UK website:
The basic viscous couple system from the 993 is retained but the viscous clutch for the front axle is now incorporated into the differential housing. The differential weighs 23kg, the clutch making up 3kg of this. Doing it this way also enables the Tiptronic automatic gearbox to be used with the 4WD system.
To minimise the parts, it was better to move the viscous clutch into the front differential and use the same clutch irrespective of gearbox. The five-speed Tiptronic gearbox is physically larger than the six-speed manual and there would not have been room otherwise, so two engineering problem birds were killed with the proverbial single stone. Porsche expect a 30 percent Tiptronic take-up on the Carrera 4.
<a href="http://www.racecar.co.uk/roadtest/porsche3.html" target="_blank">http://www.racecar.co.uk/roadtest/porsche3.html</a>
The basic viscous couple system from the 993 is retained but the viscous clutch for the front axle is now incorporated into the differential housing. The differential weighs 23kg, the clutch making up 3kg of this. Doing it this way also enables the Tiptronic automatic gearbox to be used with the 4WD system.
To minimise the parts, it was better to move the viscous clutch into the front differential and use the same clutch irrespective of gearbox. The five-speed Tiptronic gearbox is physically larger than the six-speed manual and there would not have been room otherwise, so two engineering problem birds were killed with the proverbial single stone. Porsche expect a 30 percent Tiptronic take-up on the Carrera 4.
<a href="http://www.racecar.co.uk/roadtest/porsche3.html" target="_blank">http://www.racecar.co.uk/roadtest/porsche3.html</a>
