Stasis differential mod - seeking opinions.......
04-08-2002, 01:47 PM
#11
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What kind of rear LSD are you running?
I have no direct experience with the Torsen center diff mod, but I strongly believe a rear LSD will have a huge effect on how much difference the center diff will make.
I know you have mentioned this in your example but I want to stress this. On corner exit, you have
10-20 =30
25-45 =70
35-65
By having an open front diff and LSD rear diff in this case, you have less traction relatively up front which helps the Torsen to send more power to the rear and let you be able to use the extra available bias.
Now with an open rear diff, the torque split in this example would be less since now the rear will see relavtively less of the car's total traction compared to before.
Also the front and rear traction split is not really just 30/70. Since there's more relative weight transfer along with more roll stiffness in the rear, actual traction will be realatively less than 70 in that case(efficiency of tire traction reduces as load increases).
My point is more bias in the center diff definitely helps either you do have an open or LSD in the rear. Having an rear LSD will help a lot more. Actually IMO a rear LSD should come before the center diff mod. I believe having a high performance suspension system and chasis setup is more important than this modification.
I am looking at doing this modification but I am considering either getting a rear LSD first or doing them both. If you don't mind, what kind of LSD are you running? %lock? 1way/1.5way/2way?
Thanks,
I know you have mentioned this in your example but I want to stress this. On corner exit, you have
10-20 =30
25-45 =70
35-65
By having an open front diff and LSD rear diff in this case, you have less traction relatively up front which helps the Torsen to send more power to the rear and let you be able to use the extra available bias.
Now with an open rear diff, the torque split in this example would be less since now the rear will see relavtively less of the car's total traction compared to before.
Also the front and rear traction split is not really just 30/70. Since there's more relative weight transfer along with more roll stiffness in the rear, actual traction will be realatively less than 70 in that case(efficiency of tire traction reduces as load increases).
My point is more bias in the center diff definitely helps either you do have an open or LSD in the rear. Having an rear LSD will help a lot more. Actually IMO a rear LSD should come before the center diff mod. I believe having a high performance suspension system and chasis setup is more important than this modification.
I am looking at doing this modification but I am considering either getting a rear LSD first or doing them both. If you don't mind, what kind of LSD are you running? %lock? 1way/1.5way/2way?
Thanks,
04-08-2002, 02:10 PM
#13
I started looking around to see what 4kq meant. The FSAE faq or something refers to the T2 (T2R)
type torsen... http://www.torsen.com/products/products.htm
at least regarding modifying the bias ratio using clutches, and oils etc.
ehh, pretty far from what looks like a T1 on the A4 (and bigger T1) and on the S4.
While changing viscosity does add friction and helps a limited slip, it doesn't apply to our cars as it is one big system, including the tranny. Unless one plugs the torsen housing, and install fill and drain plugs, then "slight" torsen bias ratio will be changed. Slight because well, most of the bias ratio is accomplished by the shape of the helical gears.
However, there is a trick which looks like I read also in the faq. Racers isolate the gearing housing (wrap it in sheet metal?) and can fill that inside with the heaviest oil. That should also help (T2) but if I were to go to all that trouble, I'd rather weld the gears in place.
However, his link did point me back to the product page above, and looks like they have an new product which should be a pretty good replacement to the (T1) one we have. The T3 which employs what looks like to me a planetary gearing system (a bit similar to auto tranny) means that you can set the normal bias ratio 65% rear, 35% front. That should be sweet!
at least regarding modifying the bias ratio using clutches, and oils etc.
ehh, pretty far from what looks like a T1 on the A4 (and bigger T1) and on the S4.
While changing viscosity does add friction and helps a limited slip, it doesn't apply to our cars as it is one big system, including the tranny. Unless one plugs the torsen housing, and install fill and drain plugs, then "slight" torsen bias ratio will be changed. Slight because well, most of the bias ratio is accomplished by the shape of the helical gears.
However, there is a trick which looks like I read also in the faq. Racers isolate the gearing housing (wrap it in sheet metal?) and can fill that inside with the heaviest oil. That should also help (T2) but if I were to go to all that trouble, I'd rather weld the gears in place.
However, his link did point me back to the product page above, and looks like they have an new product which should be a pretty good replacement to the (T1) one we have. The T3 which employs what looks like to me a planetary gearing system (a bit similar to auto tranny) means that you can set the normal bias ratio 65% rear, 35% front. That should be sweet!
04-08-2002, 02:18 PM
#14
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Good points....
You're point about using a rear LSD to make a higher bias center even more effective is right on. Especially because you get on the throttle just after the steady state cornering situation, but well before the full throttle corner exit situation. At that point, not that much weight has transfered to the rear, thus the inside rear wheel could have the least traction for an instant. If you have an LSD in the rear, it forces the Torsen to see more torque resistance in the rear than there really is at the ground. This will assist in getting weight transfered to the rear quicker, and to a larger extent, thus being able to take more advantage of the high bias center.
You're also right that there is more to the equation than just wheel weights, but it's not a bad simplification, just to get the point across.
Like I mentioned, however, each person's requirements depends on how the car is being used, and how the rest of the chassis is tuned. In your case, being another autox junkie, you would definitely benefit from having both a high bias center and a rear LSD. I'd have to know more about how your car performs now to be able to decide which should come first, however. In our case, the LSD came first cause that's what we could get first. And in hind sight, I think that was probably the better way to go for our situation.
You're also right that there is more to the equation than just wheel weights, but it's not a bad simplification, just to get the point across.
Like I mentioned, however, each person's requirements depends on how the car is being used, and how the rest of the chassis is tuned. In your case, being another autox junkie, you would definitely benefit from having both a high bias center and a rear LSD. I'd have to know more about how your car performs now to be able to decide which should come first, however. In our case, the LSD came first cause that's what we could get first. And in hind sight, I think that was probably the better way to go for our situation.
04-08-2002, 05:05 PM
#19
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I have the 5 speed front trak in the rear of my 914 with everything welded together. Pretty much
a pain in the pits, CV's will proabably need to be replaced once a year, sound s like the thing is falling apart...( my buddies cup car sounds identical, must 80 %),but it does work great on the track! I know some guys that played around running a spool in an Indy light car, it was faster in the tight corners, especially the hairpin, but they lost time in the long sweepers. Just backwards of what I would have thought. They believe that most of the time gained with the spool was under braking. The rear axle braking distribution wheel to wheel is always perfect. Nice write up Corey.