hrubago

Have anybody installed it on the car? Which experience?

Is important to upgrade rear diff before instalation? (I have Sti 3 rear viscous coupler 4,44:1 + front quaife ATB.)

TopBanana

Doesn't a DCCD diff do the same thing in the open position?

hrubago

Maybe. But how much for DCCD? :-) Usual combination DCCD + rear mechanical type diff. (in R180 case) in type R
Dont know how will operate Cusco + viscous center lock device + rear R160 viscous.

Absolute Shower

Sorry to butt in, but how much was your front quaife diff and whats it work like?

johnfelstead

Theo has this setup with a VC rear diff, it spins the inside rear wheel badly, you really do need a plated diff to make this work, the VC diff is quite weak LSD presure wise.

You can use an R160 plated rear diff, such as fitted to the P1.

dowser

Are plated rear diffs fitted to all v5/6 STi's?

Richard

prana

where are you looking to get those Cusco diffs from ? And how much ? I wil be after one shortly

Adam M

don't think they are cheap.

the dccd was less I think, but then it works out more once you put the control module on it, and without the control module I would expect the viscous lock up to be even weaker than the cusco one after all it is meant to be in the zero lock position.

I paid about 475 for my quaife front diff from demon some time back. Fitting is different as it is the first thing to go inside the gearbox and so would require complete dissassembly.

There is an option from modena which is exactly the same design as the quaife (not quite identical for legal reasons but almost ) which I believe is the same price, but havign seen both units in the flesh, to me the quality of the modena is significantly better, although I have only compared the external finish.

Think modenas used to be available from town end garage, though not certain if that is still the case or not.

hrubago

Front quaife: Im happy with it. The car is more predictable under throttle without straight line in curve :-). On the snow car change direction much better and quicker than without quaife.
Rear plated diff will be good addition.

Central diff cusco vs. Sti DCCD from RA or type R:
35/65 split work under all conditions in DCCD. Locking device is electromagnetic clutch - but have no function to torque splitting.

Question is how the cusco central diff work with standard viscous coupler locking device (and if the VC is necessary?) And if one axle spins then locking device will make lock and then central diff work like 50/50 split?
Cusco 35/65 tarmac diff cost around 1800 USD.

Andy.F

Hrubago
I think you will find that the cusco diff takes the place of the OE centre viscous coupler. There will be zero lsd effect from the cusco centre.

Adam The dccd has no viscous effect either, it has a 2 stage plate clutch set with variable lock up. Unless you meant the oil drag on the plates resulting in some minor visco effect when 'open' ?

Andy

Adam M

hrubago,

if the dccd locks to any degree via its own electrohydraulic diff, then torque split will change, thats why flicking it forward tends to stop the back from spinning out.

hrubago

On DCCD adjustable locking device in my opinion you can set only how much strong the locking device will lock differential function. 35/65 distribution is in the open position but in my opinion 35/65 is only torque not speed distribution. Signal for locking device is different axle speed. Then teoretically DCCD can distribute 35/65 in locking position. Maybe Im wrong. :-)

Andy.F

Adam

Don't mean to sound picky here but there is no hydraulic aspect to the dccd.

Andy

EvilBevel

Can confirm that you really need another rear diff with the Cusco. Traction is almost non existant, but the sliding is fun. Also have ATB front BTW.

I will be trying out the ATB rear diff first, but maybe a plated diff is less of a risk for you.

There is zero locking in the Cusco BTW, it's an "open diff".

hrubago

If understood well: First I have to try rear mechanical or ATB, then central diff CUSCO 35/65.
I saw CUSCO or KAAZ plate type diff for reasonable price (1300 USD). And heard also about company in UK which can uprate viscous coupler to stronger unit. Price aroun 125L.

Do you know viscous coupler specification on turbo UK and STi models?

Dan

Adam M

no problem andy, am always happy to learn.

Never taken one apart so not familiar with the actual locking, just regurgitating the terms I have seen before. How does it actually work having seen one in pieces?

Adam M

theo, it looks like your experiments wil be exactly the results I am looking for as they are exactly what I had planned for mine in order to help me irradicate those oversteery moments.

prana

I can't seem to find further information on the Cusco rear bias setup apart from being a replacement for the centre diff (as you already have mentioned). Are you sure it is an open differential ?

I would certainly like to counter the weight bias with torque bias on the chassis

edoit: I am trying to achieve the same characteristics you are trying to remove

[Edited by prana - 12/23/2003 12:51:47 PM]

johnfelstead

cusco is an open diff with a 65:35 torque split.

DCCD is a variable rate LSD (plated electromagnetic, zero VC effect), you dont alter the torque split by adjusting the lock ratio, you are adjusting the amount of slip allowed as a percentage of full lock available.

Even in fully locked mode, you can still get some slip in the centre diff as you arent pinning the diff plates, just clamping them very tightly. That is why you get the surging when you lock the diff up and do a tight turn, you are still seeing some slip in action there.

The torque split is achieved via the physical gearing of the diff carrier assembly, the LSD plates dont alter this at all, so even fully locked the static torque split is still 65:35. However the more you lock the centre diff the more torque follows load distribution.

Torque ditribution is an ever changing variable, so even though you have a static torque split of 65/35, that will change whilst the car is driven, for example in a power slide with the centre diff fully unlocked and the rear wheels spinning 100% of the torque goes to the rear wheels, so the Impreza becomes a RWD 100:0 torque split vehicle.

This is why you need an agresive rear diff with a cusco or dccd centre diff set to open, as the moment you break traction at the rear, all the torque goes to the rear wheels. Now if your rear diff is a weak LSD, that will follow the same logic and all the torque will go to the least loaded wheel, so you end up with a one wheel drive Impreza and lots of smoke, zero traction. so in Theo's case, right now he is getting 300lbft torque through one tyre, smokin.

EvilBevel

Aye

Amazing how that wears say a Pirelli

Adam M

John,

if they plates aren't pinned together, but are almost completely locked then how can the torque split still be 33:67? I can understand if this is the case when there is relative slip, but that is in extreme cases when cornering will force them to rotate at different speeds.

In a straight line with a locked diff if you treat it in your mind that they are locked together (which they will practically be) thn how can you achieve anything other than a 50:50 torque split (assuming no slip between road and tyre).

Andy.F

JF is slightly confused here

With a free centre diff you will always get 66/34 torque split, even when John is 'powersliding' the tail end there is still 34% torque going to the front. It is the %age power to the rear which will vary. This is a function of relative speed of axles * dccd percentage of the engine torque.

With a fully locked (ie pinned) diff, the torque split will be dictated by the weight on the tyres and the friction level between them and the road surface.

Anywhere in between will give a torque disribution of anything from 0/100 to 100/0 dependant on traction available.

Andy

Adam
Inside the DCCD there is a electromagnetically operated slave clutch which causes a series of ***** to run up ramps which in turn applies pressure to the main clutch pack in a similar method to a front or rear plated diff. John F had a link to a nice picture of this. I can't find it right now.

Andy

[Edited by Andy.F - 12/23/2003 8:02:59 PM]

johnfelstead

torque split is achieved via the sun and planet cases drive ratios, not via the lock ratio. If the centre diff is fully open and you are driving down a road in a high gear, so no oportunity for wheel slip, its just the same effect as having the diff fully locked as far as drive is concerned, you still have 65/35 torque split.

Drive at 100MPH and lock the centre diff, makes no diference at all in a straight line unless your tyres are not equal wear, then you would get some increase in transmition losses as the centre diff binds up and releases to take up the rotational speed diferences.

Come to a corner and then you will feel a big effect as the wheels need to rotate at diferent rates/slip angles and the load at each corner will alter, affecting torque distribution.

johnfelstead

Sorry andy, but thats not correct. I could show you some film of my car doing dounuts with an open diff, with the front wheels completely stationary (apart from the normal rolling to make the circle) and the rear wheels lit up. All the torque is going to the rear wheels, zero to the front so teh car rotates around the front axle. I can then show you another film of me doing a donut with the centre diff locked, this time all 4 wheels are spinning so the car rotates around the centre of the chassis.

Andy.F

John

A 50/50 visco centre diff car will do that, stand still at the front with the rear spinning around it, there is still torque going to the front, it just goes through the rotating front wheel, thats why 4wd cars do such good donuts !!!

Andy.F

John

The dccd is a dumb gear train, it can only ever distribute torque in a 2:1 ratio unless externally locked. The gears dictate this. Just like 2nd gear is 2:1 for example, regardless of wheelspin there will always be a 2:1 torque multiplication.

Pavlo

My car donuts no problem at all. Also, I can't unstick the front on full power, although the rear will brake away.

Once an open diff has lost traction at one side, all torque goes to that side. That's where the Anti Torque Biasing diff is different, it maintains the same torque split with only minimal grip on either side.

Paul

johnfelstead

johnfelstead

Andy, you dont understand how torque is ditributed in open diffs if you think that. Torque always follows the path of least resitance, hence why a powerful RWD car with an open diff spins one wheel and generates lots of smoke but very little acceleration.

I can show you a film of me driving a P1 in a donut if you like too, that is rotating around the centre of the chassis with all 4 wheels spinning, just like a DCCD will do with the centre diff locked. It is completely diferent to an open centre diff donut, which looks just like a RWD car. In fact if you watch an open diff Impreza doing donuts, by modulating the throttle you can see the front wheels grab for traction if you back off too much power, then if you nail it again the fronts stop grabbing and all power goes back to the rear only.

johnfelstead

watch this video for a good illustration of how an open centre diff Impreza puts all the torque to the rear wheels once they start to spin, you can also see, as simon exits the donut you get a sudden rush of torque to the front wheels as the rears take up traction (7.5 seconds into the clip). The front wheels go from just rolling at car speed to wheelspin as the rears take up grip. You can actually hear the engine note change and stutter slightly as the traction and load suddenly goes up when the rear start to grip and the fronts start to spin.

http://www.johnfelstead.co.uk/videos/22b-doughnut.mpeg

[Edited by johnfelstead - 12/23/2003 9:10:50 PM]