hrubago

I have standard turbo MY2000.
As you know, Impreza is heavy understeered car. I need to correct this (now I dont meen geometry setting - that solve it entirely in part – when you enter the curve.) Curve exiting depend on torque distribution . Of course antilift kit, sway bars etc. can helps... Main parts for me to upgrade are differentials:

1) Has anyone experience with Limited Slip differential from Sti (12kgf.m/100rpm or 20) alternatively e.g QUAIFE?
2) What about improvement in grip in curve and change characteristic to oversteer?
3) Its better to change front or rear diffs or both? Mechanical or viscous coupling?
4) Do you suggest LSD (based on viscous coupling) or QUAIFE?
5) Changed you dramatically his driving style after LSD was installed?


I heard that the standard front diifs is open type. Is it true?

Andy.F

Std UK cars front diffs are open. I believe the balance can be biased toward oversteer by using an Sti centre diff which has a different torque split. It sends more power to the rear.

I fitted a plate type front LSD to my 95 WRX RA and it certainly changed the handling but I'm not sure if I like it. Powering through a turn now the car is neutral/slight oversteer as the front really pulls round, when I lift slightly the car still runs wide. Maybe if I change the ARB to set the car with more oversteer I will achieve better balance mid turn ? I think a Quaife/Torsen type diff is probably better for the front with a plate type in the rear.

Andy

ScoobyWhite

I would like to see answers for this question too.......

dowser

I've got the Quaife at the front - it's excellent for powering round & out of corners.

However, it doesn't cure understeer if your corner entry is too fast - and if your front end is already sliding it seems to take forever for the torque to be distributed rearwards (and the problem is that 'giving gas' just drifts the front wide even more). Mine's a Euro car, so has the 12kg/cm centre - if I could do it again I'd have gone to the 20kg/cm STi centre at the same time (in gearbox too). Bloody expensive though - about £500 + fitting for the Quaife.

If it's just the understeer you want to cure a far cheaper option is to fit an ALK and adjustable rear ARB - I've fitted the ALK (not ARB yet) - the ALK improves turn-in response and allows much faster corner entry.

Obviously, a bit of negative camber helps too

In summary - yes, a Quaife front is an excellent addition....but it doesn't fix understeer if corner entry is too fast....not such an issue on track, but can be on the road. Slow in fast out

Oh, be careful when first driving hard after fitting a front diff - the front of the car will rip itself towards the inside of the corner 1st time you try it. Your reaction maybe to lift off, mine was - don't do it You get used to it quickly though.

Richard

hrubago

Im sure that Sti center difs differs from standard only in lock function - Sti locking soon. Basic function is lock when the different rpm between front and rear axles is higher than.....xxx (i know its based not on rpm but some torque in viscous coupling).
Its easy to feel it on snow. When you drive in normal condition (normal gas pedal and normal speed) the car is understeered and dont like to turn. When you try to heavy accelerate, the front wheel will spin and central diff will lock. This means that the rear wheel has now more power. It looks like rear powered car but all wheels are the same power/torque.

hrubago

To negotiate understeer is too important to me.... I had many BMW M3 and its difficult to change my driving style. :-)

hrubago

I red on MRT pages:

central LSD with 20kgf.m/100rpm makes the car bloody understeer like a pig :-)

Andy.F

Richard

I know what you mean with the front snatching for the inside of the corner Almost catches you out ! I've found myself almost taking the front wing off a car if I'm overtaking on full power as my car darts back to my side of the road

Hrubago

I think the classic Sti diff is a 40/60 rear bias (or thereabouts) torque split whilst the UK is 50/50. The sti electronic adjustment is to a clutch band which provides a varying degree of locking to the epicyclic gearing. When in the open position it splits the torque 40/60 with no LSD effect. When fully closed it effectivly operates as a locked diff (for ice etc)

As far as I'm aware

Adam M

andy, almost right except that it is 36:64 not 40:60.

It is a planetary arrangement which allows for the different torque and is only a feature of the cars with the manual lock up.

You are right in that it ranges from no lsd effect being fully open to completely locked.

The standard sti diff as on the P1 and others is a 50:50 viscous coupled diff.

Andy.F

Thanks Adam

Can these diffs be retrofitted to a 50/50 viscous diff type gearbox or are they dedicated to their own gearboxes ?

Claudius

If you want optimum corner entrance characteristics, get a 2 way front LSD. You wont regret it. CUSCO, available from www.rcdevelopments.com in the UK is supposed to be excellent stuff.

DGRALLYING

HRU

I Have a Plated rear diff with CWP(4:4) for sale if you want it?

Pavlo

Changing the rear diff to an lsd, esp a plated one, would probably create more entry understeer, followed by exit oversteer once a little power was applied.

So if you want less understeer on exit rear LSD should help, but (on it's own) it will increase entry understeer.

As for entry understeer;

Increase toe-out will reduce it, and lead to reduce oversteer later in the corner.

Increased castor should provide more positive turn in, but with less oversteer later in the bend than running toe out.

Adding front negative camber would most probably increase turn-in at the expense of front grip later in the bend.

Exactly where would like more front end grip?
Is it turn-in, just as you start feed into the bend?
Do you want more front after initial turn in, early to mid bend? Do you want more front grip while maintaining constant speed around the middle of the bend before accelerating out?

If you can be more exact there are probably more simple changes that can be made.

Paul

MorayMackenzie

Dowser wrote about the Quaife ATB: "However, it doesn't cure understeer if your corner entry is too fast" I would point out that any car, even an F1 go-kart-on-steroids, could be made to understeer if you enter a corner too fast... it's simple physics, tyres have limits, if you cross them, that's it.

I had an ATB fitted to my car a couple of years ago now... you may well have to adjust your driving style a bit if you do have one fitted, but this is simply a case of starting slow again and building up as you get used to the new characteristics of the car.

To re-iterate a post I made a couple of years ago when I had been driving with the ATB for a while: I wouldn't recommend the ATB for absolutely everyone, it could work out as a liability if not driven with some degree of understanding and/or respect... some drivers would probably be safer with a standard open diff, this allowing the manufacturer's built in understeer safety net to help them to stay in one piece.

Moray
bbs.22b.com
www.i-club.com/forums

Pavlo

Karts readily understeer into corners, solid rear axles.

dowser

Hrubago,

If you read MRT's website properly you'll also see a "...unless the suspension is set-up correctly" statement ;-)

The 20kg/cm centre just provide more resistance from the word go, hence making it 'faster' to react to my tiny, simplistic mind.

Moray - I agree, but I wouldn't be without it now.

Andy - I also found that my exit speed was so fast in the wet that when I lifted as per 'pre-diff' normal for the next corner entry to coast down for the reduced speed limit....guess the rest, lol! From the outside I suppose it looked quite professional.....

Richard

[Edited by dowser - 6/26/2002 3:11:35 PM]

hrubago

If I undestood correctly: only the center diff from STi type R with manual control has 40/60 torque split. Others has 50/50. Sti and standard diff differs in locking conditions (different viscous coupling) (or the STi has mechanical LSD?

Rear differential offer: yes but STI diff uses different gearing - not suitable for standard central diff. I must buy all three differentials :-)

I ask some rally drivers and the say me - the first use uprated front diffs. They can specify 1) condition of locking (12 kgf.m....) and prestres.....

I have possibility to ask for another one, but I dont know any about specifications.........

And I dont know about differencies in real driving conditions between quaife (torsen type diff??) and STi (visco coupling)

hrubago

what is ARB?

sorry I red carefully previous messages:

1) is really your opinion that the quaife is better than viscous type?

Adam M

ok. missing the point.

sti centre diff is viscous coupled with 50:50 torque split. this comes in 2 forms, a 12kgm and a 20 kgm the latter being more aggressive

sti also has a viscous rear lsd designated r160.

type r has manual centre diff which is an open diff that is planetary in arrangement and so has a split of 36:64 f:r. It also has an electrohydraulic lockup facility which changes it progressively between completely open and completely free, but this is not automatic depending on relative axle speeds as in the normal sti diff.

the type r has a plate type rear lsd which is also more aggressive in its lock up than the VC of the standard r160 diff. the type r rear diff is designated r180.

the front diffs of all standard imprezas, apart from some rare versions, some ras, v lims and the 22B are all open diffs. the special editions are meant to have viscous coupled lsds.

only the front and rear diffs can be changed the quaife atb or auto torque biasing differentials which are a type of mechnical lsd which lock up very progressively. These are based on worm gears being able to turn a gear, but the gear not being able to turn the worm gear when a torque is transmitted from the gear to the worm gear.


arb stands for anti roll bar i think.

alk is anti lift kit.

hrubago

Which kgm has standard turbo in center and rear?

JIM THEO

I don’t want to hijack your thread but could someone who tried a Quaife rear diff comments about noise, driveability (progressiveness/ locking speed compared to the original Turbo MY00 spec item) and cost (exact price with all the required)?
Is it direct replacement or needs some more extra parts to fit?
Thanks in advance for your answers!

JIM

TonyBurns

iTrader: (3)

I know that this may sound silly and not quite as expensive as replacing diffs but.... have you tried playing around with your tyre pressures?
On some settings you can get quite alot of understeer but by adding/removing air from your tyres you can actually get a decent ballance, its all down to what you prefer though and takes a bit of getting use to.

Tony

Adam M

bugger I worte a really long repy to this, and now it appears not to have been posted to the thread.

sh1te!

ok.

noise not an issue.

torque transfer, thinks its as smooth and linear as you can get.

dont know anyone who has changed the rear yet, but know someone who is waiting to.

final point.

pat knows most about the theory of all this lot, but unfortunately he is unlikely to read here.

the subject was covered in a thread on 22B so you could go on there and search it.

Other option is to post in the relevant forum on there and ask what you want to know. He tends to lurk on there if posts are interesting, and I think he would appreicate this kind of thread.