strongest rear diff?

[peter holst]

As I am going to install my 400 hp engine soon, I was thinking about changing the rear diff (thorsen) with the one from the lancia dedra integrale. But only if it is stronger than the alfa one.
Does anyboby know anything about that?
I?m going to use my car for trackdays and some clubrace

[Stuntz]

Dedra integrales is an open diff why would you install a weaker less sofisticated unit?

And my friend run 500 hp on it and it didnt break so why would yours on only 400 hp :)

[peter holst]

I will only install the dedra integrale diff if it is stronger than the alfa q4 one. The alfa 155 gta didn?t use the thorsen diff!

[Stuntz]

It was a race car and used a clasic diff whit LSD as used in the race cars .

[peter holst]

I know it was a race diff. What does LSD stand for?

[Stuntz]

Limited slip diferential

As torsen is how to put it adjustable buy itself . RAce difs are locked to certin percent and maintain that lock all time if torsen looses complete traction it starts to act as a normal diff so because of that toresn is good for track use as you always have grip on all for wheels and LSD is better for rally where the wheells are sometimes in the air :)

[RMB-Racing]

But isn't there a limited slip in the rear diff on the Q4..?

It?s the centerdiff which are a thorsen diff?!!

Or have I misunderstood something..?

[Stuntz]

front and centre are viscous diffs rear diff is a torsen unit.

[#84]

Front is an open differential

[Steve Webb]

I was thinking about this earlier, as I remembered the front is an open diff, BUT because the center is a Viscous coupling, if a front wheel loses grip an spins much faster than the other front wheel, the front and rear axles (virtual) will be rotating at different speeds, the VC will lock which will arrest the spinning of the front wheel that has lost grip.

Does that sound right?

[#84]

I don't know if I understood you correcly, but in the case you describe initially the front wheels will accelerate and the car looses traction, then the Viscous Coupling distributes torque to the rear wheels and the traction comes back. The opposite situation is easy and lovely to detect in slippery conditions :).

When the car understeers I really miss a front differential brake. In a Delta HPE HFE, Fiat Coupe or Focus RS you can force the front end back into the "race line" thanks to the differential brake. When the car understeers you don't loose traction and you have a considerable (negative) radial component of the traction force. The drawback with the Q4 / Integrale layout is that when the car starts to understeer the rear wheels traction will have a positive radial force component, pushing the car further out of "race line". Maybe it would be better to have the Torsen diff front with the actual chassie set up?

/A

[Steve Webb]

Hi A,

for some reason I was talking about a car accelerating in a straight line rather than your description of a car turning/understeer. I can see what you mean about the current setup inducing more understeer.

Mind you an easy remedy would be a thicker rear ARB. A few years back when I did a few trackdays with the Lancia club, lots of Integrale owners were trying, then removing thicker rear ARB's because it made the car twitchy at the rear.

[cuore_sportivo_155]

Mind you an easy remedy would be a thicker rear ARB. A few years back when I did a few trackdays with the Lancia club, lots of Integrale owners were trying, then removing thicker rear ARB's because it made the car twitchy at the rear.

And with the different weight distribution, the result might be more predictable

[jimnielsen]

I am running into this situation in slow speed 2nd gear corners where car speed drops to < 70kph..........

this is a quote from #84's text....

When the car understeers I really miss a front differential brake. In a Delta HPE HFE, Fiat Coupe or Focus RS you can force the front end back into the "race line" thanks to the differential brake. When the car understeers you don't loose traction and you have a considerable (negative) radial component of the traction force. The drawback with the Q4 / Integrale layout is that when the car starts to understeer the rear wheels traction will have a positive radial force component, pushing the car further out of "race line". Maybe it would be better to have the Torsen diff front with the actual chassie set up?

.... back to my acutal question....There is just far, far too much understeer in slow speed corners - what solutions (if any) have any of you actually tried for this problem for track use? To what extent can the problem be solved?

all input appreciated..


jimn~

[wrinx]

What tyres are you running, and pressures?

wrinx

[cuore_sportivo_155]

I suppose an ATB (torsen) diff for the front would solve the situation?

[ecl]

another front diff could maybe work, but does it exist anything that would fit. In slow speed corners, try coming faster into it, then heavy braking which will force your weigth to the front and bring out the rear. Works great:D