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Old 11-08-2006, 05:24 PM   #14
Scooby Newbie
Member#: 80430
Join Date: Jan 2005
Location: loosening gas-caps on RX8s
1997 Eagle Talon
(plus a Legacy beater)


Originally Posted by Unabomber View Post
What is a differential? A differential is a mechanical unit that allows a transference of power from one input source into two by various means.
Nope. Differentials split torque, not power. (Not a big deal, but this is just the beginning.)

Originally Posted by Unabomber View Post
Viscous: Used as the center and rear differentials in the WRX/RS.
Nope. Those are viscous limited-slip devices, not viscous power couplers (which are more like differentials). Viscous power couplers are used in cars like VWs (4-motion) and Merecedes (4-matic), but not the WRX or RS. If you can't keep straight which component is splitting and transferring torque and which is limiting slip, you are in serious trouble.

Originally Posted by Unabomber View Post
DCCD: Short for Driver Controlled Center Differential. Used on the STi. Planetary center differential in conjunction with an electronically managed continuously variable transfer clutch. And as the name suggests, it allows the driver to control the torque bias of the center diff by a turn of the thumbwheel.
One of the most common misconceptions is that the DCCD controls torque split. It does not. It controls the locking of the differential. You would not be doing anyone any favors by spreading the idea that the DCCD controls the torque split, since it is widespread enough as it is.

Originally Posted by Unabomber View Post
Torsen type differential: Used as the front (2005+) and rear differentials in the STi. Short for TORque SENsing differential. It’s worth mentioning that though Torsen is a brand name, it is the most commonly used name for this type of differential. This type of unit is also known as a helical or mechanical type. It uses gears to split power between two axles.
All (real) differentials use gears. (The exception, mentioned above, is the viscous power coupling, but those aren't really differentials; I was just being nice.) More important: Torsens cannot change the native torque split any more than a DCCD can. What a Torsen really does is lock as a function of the difference in transmitted torque (or "reflected torque," is you prefer). Type-1 Torsens do this by using the one-way behavior of worm gears. Type-2s (aka helicals) do this by using the side-force generated by spiral-cut gears to wedge the pinions against the ends of the pockets in which they live.

Originally Posted by Unabomber View Post
Which is better, Torsen or Clutch type? There really is no better. The best way to explain the difference is to use an analogy. Torsen type diffs are like the popular spring/strut combos like STi take offs + Pinks or KYB AGX + Prodrive springs. They are what they are and they do a great job. Clutch type diffs are like coilovers. They have end user adjustability and require more set-up, maintenance, and alignment. In the racing world, in theory a coilover equipped car has the advantage if perfectly driven and set-up, but they can and have been beaten by the spring/strut guys. In the end, it can be simply stated as do you want more or less hassle, adjustability, rebuildability, expense, or OEM feel?
You have got to be kidding. Please actually learn how the two diffs work and explain the difference, instead of using a misleading analogy.

Torsens respond to differences in transmitted torque. They react. They don't lock until they need to.

Clutch-packs lock as a function of input torque. They don't wait for a loss of grip; they lock in advance.

Originally Posted by Unabomber View Post
One of my favorite sayings is “Research twice, modify once”.
[edit] I won't mention my favorite sayings, but will say that you haven't done anything close to enough research to be writing a primer on this issue.

- Jtoby
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