Does this match up with anyone elses experience?
I've only driven one Subaru made in the last few years (well....I guess 2 counting the Scion FR-S...). But I have driven probably 20 90s EJ cars with various mods (or not), on an ice racing track. Most with dedicated snow tires. VLSD performs much better.
This includes my '88 XT6, which I drove for awhile stockish (coil springs), then put EJ transmission internals. The only things that changed were slight gear ratio change and VLSD center. MASSIVE improvement!!! Then I did the EJ front knuckles....Again huge.
My FWD, 1.6, Auto trans Celica is more fun to drive on the ice than any of my FT4WD Subarus were (on the same Blizzak Revo1s, which were brand-new on my loyale, and are currently on their 6th season on my Celica). And I would bet, faster.
I bet the "improvement" you are feeling when locking the center diff, is the open diff sucking so bad.
My experience, is while on pavement (center diff unlocked) you are at the mercy of your tires while off throttle, and then when you get on it in a tight bend (where AWD has it's advantage over 2WD) you just get one front tire spinning like mad. Aweful.
In low traction racing, be it dirt or snow/ice, you have the same problem when unlocked, you have the same problem. But then when you lock the center, the EA alignment (camber, caster, ackerman) means that the front looses grip first. Only with some serious weight transfer can you get the car to rotate. And only with a rear LSD can you really hold it.
The VLSD center offers just enough give to let the front tires grab on turn-in, but when you load it up, that thing grabs pretty hard. I've seen a stock 4k VLSD center diff perform in a lifted Impreza on the rocks, and was massively impressed. I am confident that it is a very strong unit when it needs to be.
I plan to run a true 4WD 5MT in my '89 XT6 for RallyX, but that's mostly for the FWD setting, as I'm considering running a welded rear. I also have the EJ knuckles for camber and ackerman correction, and will be spacing the leading rods for castor correction. Also, significant weight reduction/relocation to get the balance more were it needs to be.
I have said it before, and I'll say it again. I loved my FrankenWagon, but I HATED that transmission (RX FT4WD D/R).
Edited by Numbchux, 20 February 2013 - 12:19 AM.