EVO I-III Ralliart Viscous Coupling Unit

[EVO-00X]

Just asking whether anyone knows how to identify a Ralliart VCU and what the difference is between the OEM unit and the optional upgraded Ralliart item?
Its got to have the letters "RA" followed by a series of numbers stamped on it from memory doesnt it?
Also does anybody know what it's benefits were and where it was most suitably utilised? ie gravel duties over tarmac?
thanks in advance

 

[DOUGMO]

When I have had my box done I asked about a ra viscous unit and was advised that it is best suited to tarmac and would cause understeer on tarmac.
I have never used one in mine for that reason so cant comment on how different it is to a stock one. I think lewis has one though and he runs on tarmac and gravel so he would be able to let you know.

 

[EVO-00X]

George do you mean "best suited to gravel and would cause understeer on tarmac?"

 

[bazeng]

I've been told that they are 80/20 (rear biased)

Here is some info for ya:

from other forums:
1.

If any of you run plate lsd's front and rear in your VR4,you will know that understeer can be a issue..especially on tarmac with rally tyres The ralliart viscous coupling RA737828A1 is what I have used in my rally car..given details on the box +30% 23.1KGf/100rpm,has transformed the car when pointing into corners!

2.

The ralliart part number actually refers to a Evo 1-3 CD-CE9A Lancer Group N viscous coupling.

3.

I have a Ralliart one in my dogbox. It might still be different than the above one since there is a motorsport version as well as a upgraded street version. The one in my box won't physically fit onto the syncronized box shaft. It is too wide.

 

[EVO-00X]

What I've since been told:

Those Ralliart viscous couplings have a higher resistance to turning than the regular GSR or Evo ones. They would have more benefit on gravel or in the wet, but still worth having if you can get one for a good price. Actually I think they need more than RA stamped on them to be the real deal, RA737828A engraved by hand on the side.

Viscous couplings last forever if not abused too bad.
Do stupid stuff like running mismatched diff ratios F&R and you will cook the seal between the splines and the viscous gel will come out.

Ralliart viscous cannot and will not give a 70/30 or whatever torque split, this is plain bullshit which I suspect is Australian in origin

 

[DOUGMO]

sorry rob, i did mean more suited to gravel mate!
the guy who does my box used to look after alot of 1-3 race/rally cars and says they are
definatley the best for gravel, not so great for tarmac.
and my understanding is that they are 50-50 with more preload

 

[mrcyborg]

hey guys, i am not any expert on this so dont take this as 100%. the viscous will not vary the split ratio, this is done by gears. the uprated viscous unit will just work better and faster than a standard viscous. it will lock easier as the fluid inside is a much higher viscousity.
your torque split is done through your final drive gears. while your final drive might still be 3.909. the way they are driven are different. the number of gears between the pinion and crown wheels have a different tooth count (as well as transfer cases and output shafts) this changes the way the torque is delivered to each end of the vehicle. by counting these teeth and and working out the % difference will give you your torque split. this is why the e3 runs different transfer case ratios and out put ratios and so on from what i can work out, but never counted teeth to work out what the split is.

 

[DOUGMO]

The evo 3 runs a different transfer case becasue it has a different front diff ratio.
but agreed the viscous doesnt change the split just how it works

 

[mrcyborg]

yes thats what i ment (sorry was late). it runs a different diff ratio, but outright still the same final drive ratio. its those different diff ratios or number of teeth they are driven by that gives it its set torque split.

 

[Velocity Racing]

I think lewis has one though and he runs on tarmac and gravel so he would be able to let you know.

Yeh i have one and its definatly suited for gravel over tarmac.

from memory, Mike Dale and I tested the Ralliart one vs the stock VCU and found it took about 60-70 ftlb to slip the stock one and about 90ftlb to slip the Ralliart one.. the net effect in the car is great traction and drive off the corners, but alot of initial turnin understeer, you have to drive quite agressivly to make it work but whe you do it right its awesome.

I've done one propper full tarmac rally with it in the car and It felt good, however to get the most of of the car in the medium to high speed corners i needed to back it in just a little to balance out the understeer.

and as George and Simon etc have said no it does not alter the torque split.. they are about $1250 brand new from Ralliart (competition sales price)

 

[doommachine]

Yeah the viscous unit isn't a part of the diff, it can't affect the torque bias.

However cusco do make something that does change it...

http://www.cusco.co.jp/en/parts_product/products/tarmac_gear.html

 

[mrcyborg]

kinda looks like the one i have but havent tried yet, that would be a replacement for the stock center diff, it would be like a one way mechanical lsd, it will allow handbrake and so on because its only a one way, so only locks under excel the center diff and viscous unit can not change the torque split, remember torque split and final drive are different things.

 

[Velocity Racing]

on the subject of the Ralliart VCU I thought I would share this with you all..

I was just chatting to Ed Ordynski about setup for our car, and Ed mentioned how good (and important) the Ralliart VCU is. He said that they may a very big difference, but must be kept in good condition.

In the works cars they were replaced with a new one after every rally!!!

Just thought it was interesting..

 

[EVO-00X]

Yeah it is. So realistically if someone happens to find one in a gearbox chances are the transmission was probably out of a rally car. Reason being, it wouldnt entirely be an 'upgrade' of choice by non gravel compeditors would it.

 

[JETGSR]

I think i need to get one on a lathe and open the end up and see what it looks like inside
what the viscosity of the gel is, and weather it can be subed for something different.

personally i'll keep mine stock as the black stuff is more my thing, and i dont like understeer.

 

[rob323]

Bare in mind that the ONLY time the VCU does anything what so ever, is when you have differential wheel slip between the front and back wheels. Very common in a gravel rally car, not such a necessity for a well set up circuit car though, and for drag racing, well who cares anyway .

 

[EVOCPE]

I have an EVO box with Viscous LSD, was runnin in FWD for a while

Is that why when i take my car to the track and do a burn out only 1 tyre spins??