harj

Just wondering as a mate has an STI4 2 door and would prefer to have ABS as a safety feature?

alistair

Can't see why not, the STI saloons have ABS. You would have to lose the intercooler spray though as the reservoir goes where the ABS unit fits.

harj

Is it easy to do? as the Water Spray can be located into the boot.

I would like to know costs and time please?

Cheers

Richard F

Type Rs can't have ABS as it isn't compatible with the centre diff.

NITO

I was told the same thing as Richard. Why? I can't understand...doesn't make sense to me..why shouldn't it be compatible with ABS after all..if you were to apply biological abs (pumping the pedal) it wouldn't cause any damage so why should it with electronic abs. Unless the loom for RA's and Type R's don't have the abs wires built in, since the looms would more than likely be different for these!

Nito
ps...why not just buy a P1

Stupot

I believe the reason is space under the bonnet. The ABS system is kept right over in the left hand side behind the headlight. If u have a space there, then I cant see why u cant have the ABS fitted. I may be wrong but Centre diff adjustable cars may have some other equipment fitted there instead of the ABS.

Cheers
Stu

Richard F

Well I'm always one for a bullsh1t theory so how about...

The centre diff can't cope with the very quickly changing wheel (and therefore axle) speeds that ABS would cause.

I can't believe that under-bonnet space is the cause of it as that's not to tricky to overcome.

As a side issue I was reading the Mitsubishi site about the Evo VII and it appears that their new active differential with normal, gravel and snow settings is disconnected when you pull the handbrake to allow handbrake turns. I don't believe the Subaru diff offers that type of ability so maybe that's something to do with it as well...

NITO

Rich,

The new STi 7 RA apparently has this too

As for different wheel speeds and axles can't cope etc...how about when you lock up the front coz you don't have ABS! Interestingly enough it seems that you can handbrake cars (according to Evo) with the adjustable centre diff but not those without as it causes damage. Stange then that locking the front on an RA doesn't cause damage like locking the rears on a normal scoob!

It's also true that the water bottle sits where the abs should go, but I heard that the reason it wasn't possible was due to the centre diff!

Richard F

Aaah, my theory allows for front wheel lock up under heavy braking because it's the rate of change of wheel speed that I'd guess is the problem. The diff can handle slower changes in speed but a rapid slow down then speed up (ie when the wheel locks and unlocks) is too much for it to cope with.

Hopefully a diff guru will turn up soon and put us all out of our misery!

NDT

Think it's the other way around....having an adjustable centre diff makes it difficult to tune the ABS properly, rather than the ABS affecting the diff.
I think it's because the driveline characteristics are changeable, and to get ABS to work properly you want them permanently fixed - hence OK on non-adjustble cars.
That's why the P1 doesn't come with an adjustable diff - ABS is a bigger benefit than diff adjustment.

AndyMc

NDT

Thats how I understood it too.I think the problem is that you can completly lock-up the adjustable centre diff which means the wheels can only go the same speed.

The abs works by looking how fast each wheel is turning.If three are doing 50 mph and the other one is rapidly slowing down the ABS knows that wheel is starting to lock and releases it.This can not happen if the adjustable centre diff is locked up (slider full forward).

The viscous centre diff on the P1 and the UK cars never locks up completly and still allows the wheels to turn independantly enough for the ABS to work properly (on higher grip surfaces).
Its a different story on ice or snow though where it acts more like a locked up diff. I reckon this is why the ABS on Imprezas is so crap in the snow and ice.

By the way if an off-roader has selectable 2wd/4wd and ABS, then the ABS turns off when 4wd is selected for this reason.

Andy

Richard F

At risk of really looking thick....

But if 3 wheels are turning and the ABS tries to release the other, wouldn't the rear or front diff take care of that by punting more power from left to right (say)? I guess there could come a point where it can't do that though so, ok, that sounds reasonable enough to sink my theory!

NDT

don't really understand what you mean....wouldn't you need to be giving it some power at the same time as braking enough to lock a wheel?

Richard F

Hmmm dunno - I think i've lost this a bit.

What I'm saying is that imagine you're going in a straight line and you brake hard. All wheels slow down. Then the front right locks. This means the transmission would try to send the power to the wheels with least resistance (ie not locked). Granted if the centre diff is locked then it can't go to the back but it could go to the left front wheel. When the wheel unlocks, the power would go back to it.

You wouldn't need to be on the gas to do that - the engine is making power even if you're not accelerating.

Is this total @rse or have I just lost the plot (or both)?

NDT

but unless you're going really slowly, wouldn't the engine (on closed throttle) be drawing power rather from than delivering power to the driveline?

i.e. engine braking.

Nick

adam99rs

The center diff thing sounds like a load of poop to me. Harj, on my car, I swapped in a '96 WRX STi RA tranny in my car, and retained my non-lsd rear end, as came stock on y U.S. spec 2.5 RS. I just had a V4 STi motor swapped in, and as far as I know, the ABS is still working, as I did not change the ABS sensros, ump, etc...all remained stock. I am using the Prodrive/Alcon fron brakes though,,,much better than the 2 pots that come o the front of the 2.5RS.
I cannot fathom why the ABS would not work with the adjustable center diff, unless you had the diff fully locked front or back...then I could see the ABS getting confused. What is the torque split on a 96 STi RA center diff? Whatever it is, it works more than well with the ABS that came originally on my car.

harj

Can someone tell me where I can have it fittef then as I know of 3 Scoobies that would require it?

Richard F

Dunno NDT

Isn't engine braking more a function of the gearbox because if you're in 4th you'd get less engine braking than in 3rd.

From a purely physics (and therefore boring) point of view, power is the rate of doing work and the engine is still "work"ing because it's still combusting fuel, the pistons are still turning the crank etc.

I'm gonna give up on this one I think cos I really am not sure about this!

NDT

easier to think of it this way -
at closed throttle the engine makes enough power to keep it turning at idle speed.
Over idle speed on a closed throttle, friction and pumping losses are higher than the power being produced - so the engine is absorbing rather than producing energy...hence engine braking.
You get more enigne braking in 3rd than 4th,because you're raising the engine speed,so you're getting more friction and pumping losses.
Nick

NDT

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by adam99rs:
<B>The center diff thing sounds like a load of poop to me. Harj, on my car, I swapped in a '96 WRX STi RA tranny in my car, and retained my non-lsd rear end, as came stock on y U.S. spec 2.5 RS. I just had a V4 STi motor swapped in, and as far as I know, the ABS is still working, as I did not change the ABS sensros, ump, etc...all remained stock. I am using the Prodrive/Alcon fron brakes though,,,much better than the 2 pots that come o the front of the 2.5RS.
I cannot fathom why the ABS would not work with the adjustable center diff, unless you had the diff fully locked front or back...then I could see the ABS getting confused. What is the torque split on a 96 STi RA center diff? Whatever it is, it works more than well with the ABS that came originally on my car.[/quote]

it would (probably) be ok so long as you never had the centre diff fully locked up. Also,the lack of a LSD at the back would help.
Nick