I got an old school 1989 Legacy RS turbo with lots of tricks. But recently fitted a plate style front LSD diff. Still got the viscous LSD rear and viscous LSD center.
My question is: When the front and rear diffs bind and put load on center diff what happens?
Does the center diff slip and put power to front or back?
Does the center diff lock up?
2nd question: What is the power split under normal driving?
For you information the gearbox I use is from a 1993 WRX RA and is close ratio.
Center diff works just like any other viscous LSD. It keeps the split pretty close to 50/50 front/rear, just like your rear one keeps it pretty close to 50/50 left/right. It gives some slack of course because wheels travel at different speeds when the car is turning, but it tries as best it can to keep it at 50/50.
Sounds like one awesome car you have... another reason to move to NZ
It's a bit odd I find to have the plated diff up front with a stock VLSD in the rear. Usually you want a relatively open diff up front as a plated or stiffer diff up front causes understeer. (Assuming the plated diff is set up to lock fairly easily). Do you know what it's locking characteristics are? But it's all relative to the rest of the setup and quite the black science.
A helical front LSD (which acts relatively like an open diff in terms of turn in), 12 or 20k center and plated rear seems to be the ideal setup.
Looking to do a similar setup this year in my car... the aging center and open diffs are killing me at the moment.
The STi "upgraded" center diffs cause ridiculous understeer.
I drove an RSTi we built a 5-speed dogbox for. PPG Helical front diff, Cusco 1.5way rear, and a 20kg center diff.
It understeered driving through parking lots, and taking it around our ghetto skid-pad, it couldn't go any faster than the Forester.
That center diff was quickly replaced by a stock center diff, and the car rotated much more easily on the street.
For Rally, I guess you could use a "stiff" center diff to help with on-throttle rotation in the dirt.
Our rally car is using a PPG helical front and rear diff, and a stock center diff, and the drivers claim it's unbeatable. Wait until they get ahold of the helical center diff!
We are running a Cusco plated center and front diff and the viscous rear with no problems yet. The car rips on dirt. But also has upgraded brakes with bias adjustment, which also helps to set up the car coming into corners at rally speed.
Grant Hughes
Denver, CO
http://www.nocoastmotorsports.net
