Being as my Sti8 UK hasn't got DCCD-A. What handling mods should I choose?

Already fitted a Strut Brace and springs are on order/

Is there a replacment centre diff that would alter the balance from 50:50 to a more sensible 65:35 ?

Thoughts please

 

Modena, but not cheap

 

Do modena make an epicyclic centre diff unit? I know they did do a helical gear type centre diff, but I can't remember it being torque biased to the rear... not that this can't be the case, of course, but I have only heard of 50:50 distribution helical gear units so far. Would be interesting to know if they do an epicyclic unit, and how they provide LSD functionality on it.

 

I always thought the standard diff unit was set at a 60/40 split [rear biased], as you would only get 50/50 when using a diff lock. Forgive me if i'm wrong but 50/50 would make it hell of a **tch to steer round corners at speed. Plus, on initial take up, the centre of gravity shifts rearwards, thus generating more down pressure on the rear, so pushing more torque to the front wheels will only create wheel spin.

 

Therein lies one of the big reasons why standard scoobies tend to understeer more than type R / type RA cars which run epicyclic centre diffs with a more rearwards torque bias.

 

From memory its 60/40 (front/back).

 

The regular cars have regular bevel gear centre differentials with a natural 50:50 torque balance.

The Type R/RAs run an epicyclic centre differential unit with a natural 34/66ish front/rear torque distribution.

I don't know where a 60front/40rear split could be obtained, unless it were drop gear ratio related.

 

So whats the solution other than buy a Jap Spec car ?

 

Buy a jap spec transmission and rear diff?

Or maybe just change the centre diff unit in the transfer case.

 

Thats what I have been thinking (Change diff in centre case), but I don't know anyone else that has done it and if (any) it makes improvements

Steve

 

oops. Modena don't, not sure where i imagined that one from, but Moray, haven't you got the electric diff with no ecu or power to it , so permanently 65:35?

Town end garage, Maxspeed, BGRS, can sell and fit just the dccd diff (and the rest of the necessary kit, if you want) Grade A and other breakers can supply the bits and you fit. I've been toying on an off with doing this to my P1 (to make a sneaky Type R). Bits needed, DCCD diff, diff ecu,handbrake switch & wiring display led (optional, as you know when its locked!),control wheel, and probably swap the rear diff for an R180 plus shafts, hubs, brakes etc. Problems? ABS won't work as no ABS rings on the back and as locked diff would possibly mean all 4 wheels locking under braking the ABS could then disable the brakes - solution ? Leave the diff open or pull the ABS fuse, don't know what would happen in the semi locked situation tho?

 

All the diffs in Scoobys end up with a 50:50 split! The epicyclic gears in an electronic unit still split the same.Fr all Jap cars the planet gears are all symetrical, the transfer gears in the centre diff have a 31:31 tooth count, and the front and rear diffs are the same on any car (3.9, 4.1 or 4.4). the uk versions have 30:33 transfer gears and an extra tooth on the rear diff pinnion only, when all the maths is applied we still have a 50:50 split. The operation of a Viscous centre diff resists the front and rear end varying in speed, the bigger the difference in speed the harder it resists thus appling more force to the end which is 'spinning' crude but effective. The electronic centre diff is a plated LSD (like Sti rear), but instead of having a factory set pre load it has an electromagnet and mini-clutch built in which allows the preload to be set by the driver, hence the switch says 'L' for lock, in other words the diff is locked solid allowing no variation in speed front to rear especially noticable at slow junctions. The diff however will slip under high load especially when warm! It should be noted that superior braking and traction are obtained when on lock as neither end will 'lock up'.
By the way Modena have made a Plated centre diff which is currently in a test car at Town end garage, it isn't driver adjustable, but with correctly set pre-load and ramp angles seems to give excellent all round performance.

 

Now I really don#'t know what to do

All I'm basically looking for is a good all round set-up that will hopefully reduce understeer when charging round the Nordschleife and Donno etc.

I just think the standard set-up isn't quite good enough for this albeit fair for road use (most of the time )

I'm hoping that the Prodrive springs and alignment will improve it but need to be thinking about the next step after this if I am still unhappy.

I like the idea of getting all the bits from Grade A or somehwhere though. Wonder how much ?

Steve

 

bump steer and 4 wheel alighnment would fix it would it not?

 

Not convinced, but it is one of the options afer Springs

Steve

 

Mouse,

Re "All the diffs in Scoobys end up with a 50:50 split! The epicyclic gears in an electronic unit still split the same."

This was discussed at great length in the past... the outcome was that the epicyclic DCCD in open state does indeed provide a ~65r:35f torque distribution. Can you tell us why you believe this is not the case?

Moray

 

Raised my eyebrows a bit when I saw that too, but I suspect Mouse knows his stuff if he's the same Mouse that works for TEG.

Car certainly feels like it has a rearward bias when DCCD roller is down, and if it was simply a case of lack of preload in the centre diff, it'd be understeery, rather than oversteery under hard acceleration.

 

I made the mistake of arguing with andy f about this and he explained it rather well.

To ask simply, why is it that viscous centre diff equipped cars spin their front wheels off the line whereas open dccd equipped cars spin their rear wheels?

I can provide photos if necessary!

 

No photos necessary, seen enough, and know enough about how the handling with the two types of diff, erm, differs to know the DCCD cars do have a marked rearward power bias when the diff is open, especially compared with viscous centre.

At same time though I'm sure that Mouse has seen enough of these diffs in pieces to know how they work, so must have reason to say what he has.

Was your "argument" with Andy on here, and if so, do you know the thread ID? Would probably save a load of repetition if we could see it.

 

grease monkey,

wasn't making the point to you, that was to mouse!

my arg was with andy on here and I had to do some serious humble pie eating.

It is the same thread moray is talking about, but I will alert andy to this one to see what he wants to add.

 

Mouse, the planet gears in the dccd are indeed symmetrical however the design is such that the planet gears can rotate on their axis in addition to driving the planetary carrier.
The torque transferred across the gears remains equal due to their identical tooth count. The torque driving the carrier is greater as the lever arm length has doubled.

As mentioned previously, this is why a viscous ctr diff car will spin the front wheels during a hard launch and an open dccd car will spin the rears even with the additional weight transfered to the rear during acceleration.

Andy

 

Steve - having bought a wrx originally, I didn't even have the front LSD in mine, so I had to start from the very very beginning

Basically, you would be amazed what a difference changing components such as the rear antiroll bar will make.

However the biggest difference on the newage cars comes from the springs. Although adjustable coilovers are obviously the ideal, if it's your everyday car you will be amazed what a different the Eibach or Prodrive springs will make.

I found that the standard STI8 was actually worse than a standard STI7 because they made the shocks stiffer, but did nothing about that silly ride height, and so you get the old Touring car style bounce going on. Never good for confidence

Once you have brought the centre of gravity down, upgrade to a larger rear ARB and solid drop links and get the geometry done at TSL and you will not know yourself.

Personally I would also recommend both front and rear strut braces. Almost everybody said to me that the newage cars don't need them as they are so much stiffer. Bullsh1t! They made an absolutely massive difference, not only to fast cornering but also to stability when switching direction (ie through craner), mid-corner adjustability via the throttle, and also braking stability and increased ability when braking and turning.

I am now in two minds as to wether to upgrade to a plated front diff. The car is so nicely set up, and so adjustable in the twisties and on-track, it almost feels like cheating to get a front LSD.

 

Ed,

Thanks

Front brace already fitted and I noted an improvement

Springs are on order

Alignment will happen

I will go from there, but will probably go a simialr way to you next.

Having said all that the DCCD-A should be fitted to UK cars standard

Steve

 

It will. Not til next time round tho, although next years special edition will have it I believe.

Make sure you get the geometry done at same time as springs, as the standard geometry wont be as effective after changing. Not that its effective anyway

I have also found lightweight 17's to be much more effective than 18' wheels, and that has been commented on by several people with similar chassis setups but 18' wheels who have driven my car.

 

cusco supplies a 35-65 center differential,not adjustable

 

I believe you will not satisfied with front LSD due to more understeer in the edge, a better rear LSD diff (Quaife) or center will helps you more IMO but it depends also from how over/understeering you prefer your car.
JIM

 

Prodrive springs arrived today

Will be having the geometry done along with the spring fitment at Beechdale.

Just need to book it in now.

Ed,

Where have you heard that DCCD-A is being fitted to the next generation ?

Steve

 

I've heard that all wagons have a 60:40 split while saloons (with fixed diffs) are 50:50.

I have a dyno plot of my 2nd gen leggy wagon which proves the 60:40 split and was shown a plot taken at the same dyno of an impreza saloon which proved the 50:50 split. On that evidence it could be a leggy / imp issue, but I've heard elsewhere that Subaru gave the wagons more rear bias because of the extra rear weight.

 

Steve,

The UK is getting the DCCD-A from Feburary. Brief details are on the Subaru homepage of my website.

Regards

Iain
www.litchfieldimports.co.uk

 

Steve - from someone well placed within the dealer network