02 2.5RS questions

The Subaru All-Wheel Driving System — Four Types
All models equipped with the five-speed manual transmission feature a viscous coupling center differential to split the power 50/50 between front and rear wheels. The viscous coupling responds to wheel slip and transfers power to the front or rear wheels with the best traction.
Featured on most Subaru models equipped with the 4-speed electronic automatic transmission (4EAT) is Active All-Wheel Drive. This system uses an electronically-managed continuously-variable transfer clutch. This All-Wheel Drive system can anticipate wheel slippage and transfer power to the front or rear wheels even before slippage occurs.
Impreza WRX models with the optional four-speed electronic automatic transmission (4EAT) also feature Variable Torque distribution (VTD) All-Wheel Drive.
he Subaru Outback H6-3.0 VDC combines VTD with a new stability system called Vehicle Dynamics Control (VDC). This is the most advanced All-Wheel Drive that Subaru has ever offered in the United States. - [link to VDC Piece]
Variable Torque Distribution (VTD) All-Wheel Drive uses an electronically controlled hydraulic transfer clutch that works with a planetary gear type center differential to control power distribution between the front and rear wheels. Under normal driving conditions, the VTD system splits power 45% front and 55% rear to deliver more of a "performance"driving feel. The VTD All-Wheel Drive system responds to wheel slippage by sending the power to the wheel or wheels with the best traction.

The Subaru All-Wheel Driving System keeps you safe and sound by adjusting to changing road conditions in a split second, providing outstanding traction on virtually any wet or dry surface in any weather.

Continuous All-Wheel Drive: Simple, Effective, and Reliable
In vehicles with the 5-speed manual transmission, the All-Wheel Drive uses a viscous coupling in a center differential inside the transaxle case. The viscous coupling contains a series of opposing discs attached to the front and rear output shafts, surrounded by a silicone fluid. In normal operation, power is distributed equally between the front and rear wheels (50/50 power split). Slippage at the front or rear wheels causes a rotational difference between the front and rear discs in the viscous unit, which then shears the fluid.

The shearing action heats the fluid, causing it to thicken. As the fluid thickens, power transfers from the slipping wheels to the wheels with the best traction. When the slippage ceases, all the discs turn at the same speed, restoring the 50/50 power split. The process is quick and imperceptible to the driver and passengers.

The continuous All-Wheel Driving System is simple, compact, and virtually invisible during operation. Its traction adds a significant margin of safety on slippery or unpaved roads, and enhances dry-road handling.

Active All-Wheel Drive
Subaru models equipped with the 4-speed electronic automatic transmission (4EAT) employ Active All-Wheel Drive. Active All-Wheel Drive optimizes power distribution before slippage occurs.

Instead of a viscous coupling center differential, 4EAT-equipped Subaru vehicles feature an electronically managed variable transfer clutch in the transaxle tailshaft. Power transfer is governed by slippage in the clutch plates, which use a special friction material that easily handles the loads generated during power transfer.

The electronic Transmission Control Module (TCM) controls the All-Wheel Drive multi-plate clutch. Active AWD can adjust the power split in an instant, depending on many input factors. If the front wheels begin to slip, the TCM increases hydraulic pressure on the clutch, sending power to the rear wheels. As the front wheels regain traction, the TCM reduces pressure on the clutch, increasing slippage of the plates and transferring power to the front wheels.

Intelligent Control
With Active All-Wheel Drive, the TCM monitors input from speed sensors on the front and rear output shafts and also takes input from the throttle position and transmission. All of these factors cause the TCM to choose how aggressively it adjusts the power split.

Subaru Active All-Wheel Drive varies the power split according to how you drive the vehicle. Under acceleration, weight transfers to the rear, and the system responds by transferring more power to the rear wheels (in a front-wheel drive vehicle, this weight transfer on acceleration can cause wheel spin, compromising traction). When braking, weight transfers to the front of the vehicle, and the All-Wheel Driving system transfers power to the front wheels to help reduce stopping distance.

Compared with standard front- or rear-wheel drive, All-Wheel Drive also enhances cornering performance. When you enter a turn, lifting off the gas and applying the brake transfers power to the front wheels for greater steering control. As you exit the turn and accelerate, power transfers to the rear wheels for added traction under acceleration. Power transfer occurs quickly and imperceptibly, just as it does with the continuous AWD in a manual-transmission.

Limited-Slip Rear Differential
Many models in the Subaru lineup feature a viscous limited-slip rear differential for even greater traction capability. If one rear wheel loses traction, the differential automatically diverts power to the other wheel. A viscous limited-slip differential not only helps traction in slippery on- or off-road conditions, but also serves as a cornering aid. As you enter a curve and weight transfers to the outside wheel, the inside wheel can lose traction. The viscous limited-slip differential transfers power to the outside wheel, which has greater grip.

VTD All-Wheel Drive
Impreza WRX models with the optional four-speed electronic automatic transmission (4EAT) features Variable Torque distribution (VTD) All-Wheel Drive. The new VTD system uses an electronically controlled hydraulic transfer clutch that works with a planetary gear-type center differential to control power distribution between the front and rear wheels. VTD All-Wheel Drive splits the power 45 percent front/55 percent rear, with the slight rear-wheel bias enhancing the performance driving feel. VTD All-wheel Drive constantly monitors throttle input to account for weight transfer and responds to driving conditions to continually optimize power distribution on all road surfaces.

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All of us are forgetting the main advantage of the Auto-WRX: the AWD system itself. When we talk of "Rally Proven", the "proof" is actually missing in the Manual-WRX. Here is the reason why:

The VTD-AWD system of the Auto-WRX is the most advanced AWD system of Subaru, with a true torsen (torque sensing) planetary gear center differential, which works in association with electronically controlled continuously variable multi-plate clutch-packs. The torque split is at 45/55, with a slight rear bias in power, in normal driving, unless more is needed front or back. This system equals in sophistication and effectiveness, the best AWD systems currently available in the market including the Audi Quattro (not the "Quattro" present in the Audi TT, which is inferior to the VTD-AWD). The VTD-AWD system is conceptually identical to the AWD system present in the World Rally Conquering Subarus, the significant difference being that the WRC cars have driver adjustable torque splits and are much more of a heavy duty kind. The hardware otherwise is identical in design. The Rally Subarus also have a true auto-manual transmission, which is actually a clutch-less manual, but the underlying AWD system is better adaptable to the Auto-WRX, not the manual-WRX, due to which the manual-WRX soldiers on with an AWD system that is essentially tractor-technology. "Gets the job done" but nothing to write home about.

The other Auto-Subarus do not have the torque-sensing center differential and drive more like a FWD car in normal driving.

The manual WRX on the other hand, has the same Viscous coupling AWD system present in all other manual Subarus, which is a reactive system, as opposed to the proactive nature of the VTD-AWD system of the Auto-WRX. The viscous fluid which is used to transfer torque front/back needs slippage before it can react and transfer torque. Also, since differential lock is acheived due to the viscous fluid being twisted (unlike the torque sensing incredibly sturdy planetary gear differential in the Auto-WRX), the torque-transfer is both slow and in-efficient. The AWD system of the manual WRX cannot be compared with the Audi Quattro or any other sophisticated AWD system. It does not have the breadth of operation (cannot transfer the amount of torque front/back like the VTD-AWD), the reactiveness (reacts slowly due to its very Viscous coupling nature) or the rapid torque transfer characteristics (due to the "reactive" nature of the system) of the VTD-AWD equipped Auto-WRX. With the Viscous coupling AWD system present in the manual-WRX, Subaru certainly would not be winning many rallys....just a heads-up.

Everything else remaining the same, I would have preferred a manual in the WRX. But in this particular case, everything else is not the same. Far, far from it. Let us face it - we admire these cars for their AWD systems and not for their "manual gear shift capability". So on that criteria, the Manual-WRX has a huge and glaring deficit. just my 2c

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