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Old 04-09-2011, 12:53 AM   #41
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Join Date: Oct 2004
Chapter/Region: NESIC
Location: Wayland, MA
2001 Lexus ES300,
2005 Outback XT


Originally Posted by 09rexwagon View Post
The 06-07 WRX have 3.7:1 FD ratio. You need 3.9...VCs in the r160s are weak anyway...What sort of driving do you intend to do? Autocross? Track? Why are you so concerned about having 2 tires off the ground?
Automatic 06-07 WRX is 3.9, direct swap into the 08+. Also 08-09 Legacy GT 5MT uses the 3.9 VLSD. But really only worth it if you get it cheap. Totally agree on the value of the VLSD.

I always spin the inside front on corner exit on the track. I've taken to letting it spin, I figure that will transfer some torque to the rear.

Originally Posted by Midway View Post

You were recommending a quaife or OBX diff. Do you have any idea why the diff manufacturers don't specify anything past 07 for the R160? I've read somewhere that the differential case may need to be slightly modified for the Cusco diff.

Also, reading this thread
if this is correct, do you have any idea of the difference in compatibility from an 04-06 or 07 STI rear end in a 2008-2011 car? Just wondering if all the mounting, stub axles, and drive shaft are compatible.
The aftermarket manufacturers may have not tested their stuff with the latest hardware. The R160 is basically the same, you can swap them around from almost all other Subarus, but the case may have changed over time.

The STI, in additon to having different LSD technology, has a higher grade R180 diff. There are tons of threads about swapping one into a WRX. There are some compatibility issues and choices to make about what parts to swap, but it can be done.

Originally Posted by Midway View Post
Essentially, the STI and WRX are the same... since the Torsen type diffs on the STI only kicks in when there is a torque difference (wheel begins to spin), and the WRX applies the brake on the offending wheel, effectively giving the same result - conservation of traction. However, if you drive like a maniac for an extended period of time, the brakes will heat up some. Considering BMW uses this exact same technique is heartening.
Well that is not really true for a couple reasons. First the Torsen type doesn't need any wheel spin at all to transfer torque, it is not when "wheels begin to spin" it is when a traction difference exists. That is the really neat thing about Torsen diffs, they are very quick to react. The VDC needs to sample some wheelspin before reacting.

The other problem with this scenario, is that the WRX VDC system couples braking with power reduction. I've driven with the VDC on to see what happens on the track, wet and dry. It will brake the inside front wheel when it spins, but it also shuts the power down so you bog. Any possible performance benefit is taken away by that, making the system not very useful.

Selective braking is not a bad idea though. I recall the great upset when the Caliber SRT-4 came out with the brake-lock differential instead of the Quaife that our Neon SRT-4s had. The SRT engineers pointed out that braking one front wheel could transfer way more torque than a Torsen can, being fixed at a bias ratio, commonly something like 4:1. And think our VLSDs are only moving 4kg-m (2.7lb-ft) of torque for every 100 RPM speed difference between axles. That ain't much.

The VDC could be very useful if it had a performance program that didn't kill the power.

Our crappy AWD with silly viscous center diff still gets us around pretty well. So much so that there are tons of other mods you can do before the lack of neato LSDs are really holding you back.

I am thinking lately that the handling benefit of AWD isn't in LSDs. The future has been laid out by Mitsu and Honda, it is about controlling distribution of wheel *speed* not just torque.
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