My 131 abarth (never ending) story - 2017 season updates

[miro-1980]

Re: Torsen


I am trying to fit a TorSen LSD into the Abarth diff housing.I want to predict behavior of the Torsen as compared to friction plate diff I have been using

My old friction plate LSD was rated 45% , meaning 45% of torque is passed to the wheel with traction , while 55% is passed to the spinning wheel.

What TRB ( Traction Ratio Bias) would that be in Torsen LSD :

My calculation shows it would be 1.2:1 1.2/1 = 55% /45%

Is this correct ???

Can any body assist in understanding this ?

Miro

[Urbancamo]

Hi Miro

Firstly, you cannot compare clutch LSDs to Torsen only by comparing their values. They are both very different in RWD cars and they will produce different handling characteristics.
Torsen will act like open differential when there is no wheelspin occuring or when you are coasting/decelerating. At the same situation cluch-LSD is partially locked depending of the preload of the clutch packs. The other thing is the cam profile between gears wich is pushing the clutch packs. There are 1, 1.5 and 2-way diffs around.
1-way means locking will not occur when decelerating. 1.5-way means some locking occurs when deceleration. 2-way means it's fully locked when decelerating.
Usually most RWD diffs are 1.5 way, they lock up some amount in deceleration to make car behave more logically.
This is both good and bad depending on the situation. If you have two similar cars with both differentials (clutch and Torsen), it's easy to compare how different they are.
Even the Torsen is more modern and sophisticated, no one really uses them in competition use. No matter if it's RWD or FWD, it's always clutch LSD with pretty high preload. You see preload values of 6-12 kg's in RWD cars and 15-20 kg's in FWD cars.

Secondly, if your LSD has 45% locking ratio, it means that 72.5% of the drive torque can reach the wheel with higher grip when the other side with lower grip is reveiving only 27.5%
Not 45/55% !

Lets compare to LSD with 25% locking ratio: side with higher grip gets 62.5% of the torque and side with lower grip receives 37.5%.

This is commonly misunderstanded thing and no wonder why because these things are hard to imagine!

You can calculate TBR when you know locking ratio. 45% locking ratio means 2.63 TBR. 25% locking ratio means 1.67 TBR. I'm not posting the formulas here, they are readily available in the internet.
So lower the locking ratio, lower the TBR obviously.

In Torsen differentials you generally see torque bias ratios of 2.0:1 - 3.0:1, this also depends the model of Torsen Diff. Usually Torsen Type-2 differentials (like Quaife) with paraller gears have TBR around 2.1:1, not more.

T

[Guy Croft]

Tommi

MODEL POST!

The breadth of your technical expertise on this subject is mighty impressive as I have also remarked in Steve Hinson's thread.

You are widely admired here.

Thank you for sharing your expert knowedge in a very readable way (esp considering your native language is Finnish not English) and generously devoting time to answering things few others could.

G

[miro-1980]

Hi Tommi,

Your post clarified my thinking and it was very interesting . It seems we all use terms we do not always understand ( at least I seem to be in this group).

The LSD of 45 % means that 45% of 50 % torque delivered normally to each wheel is transferred from the the slipping wheel to the wheel with the grip. OK this is clear.

Now, the Torsen drawbacks.
Old type Torsens ( Type 1 and Type 2) required that both wheel have some (at least minimal) resistance caused by traction. As Torsen acts as a torque multiplier, when one wheel is off ground it acts just as an open diff: one wheel spins freely and the other diff is not spinning at all - it strands still. The result is that the cars is not accelerating or in extreme case not moving at all. This is an obvious drawback causing Torsen not to be suitable for rallies ( both tarmac and gravel). This was overcome by Torsen Type 3 R ( rally). This type of Torsen in addition to the helical mechanism have friction plates just like in normal clutch LSD. These friction plates provide the pre-load and prevent a wheel to spin freely and engage from start , until the helical mechanism gets engaged.

I also understand that new Torsen designs have mechanisms other than friction plates which provide the same function. Some of them use springs to provide the initial pre-load. Nevertheless it is said that Torsen is not recommended for uneven surface rallies (i.e gravel or forest)

My question is what mechanisms (other then plates and springs) are used in Torsen diffs to provide pre-load.

Re Trosen Type 3: I understand that Torsen type 3 is really designed as a center differential for 4x4 cars.


Note on language: Torsen (or rather "TorSen") is a brand name. Quaife is not a Torsen though many would casually call it by a generic name of "torsen" ( like many still use "hoover", or "halda") by virtue of its construction ( not manufacturer). Among current manufacturers of torque sensing diffs are Torsen (TorSen), Detroit (trutack) and Quaife (ATB). All are differently designed but achieve the same end result. Many call the all them Torsen differentials while Detriot and Quaif are only torsen differentials. This is not just semantics. This is point of order

Miro

PS : This sometimes is frustrating . I use Halda for a Haledex made mechanical trip meter. Some us "halda" for any trip meter.
Recently I followed a lead for vintage a brand new "Halda" somebody found in his granddad's garage. It tunred to be a Bratz electronic unit. I was not very happy, but for the guy that gave me the lead any trip meter is a "halda". Too bad it is hard to hear his Halda was pronounced with a small "h", while mine with capital "H" .

M

[Urbancamo]

My question is what mechanisms (other then plates and springs) are used in Torsen diffs to provide pre-load.

My own daily driver runs a rear torsen differential wich has 6 kg's of preload. If you lift the other rear wheel off the ground, you have to use force to make this wheel spin. It's miles away from open differential. There is no clutch packs, the preaload is made by careful design of worm gear angle and their pressure to diff housing.
I heard this design is copied from some Subaru differential. I don't know if this true or not.

I have tested this differential in conditions where your other rear wheel is in dry tarmac and the other is in wet, slippery ice. Car is placed at steep uphill. It just goes even the difference in grip so huge. Accelerating the car feels similar your clutch is slipping a bit, but otherwise this extreme condition is nothing to worried about.
Try that with open diff or worn out clutch LSD. It isn't going to happen.

The difference in rallying conditions compared to proper clutch LSD is still huge. I like the way proper clutch LSD works especially at corner entry. Rear end follows the car very precicely depending of the amount of throttle. Clutch LSD is partially locked at corner entry and this greatly helps RWD handling especially at slippery conditions.
In the same situation this Torsen diff feels somewhat similar than open diff. Rear end feels bit uneven and "loose" and you don't know exactly what's gonna happen next when you apply the throttle.
These things are hard to explain, only by driving the two different cars or two different LSD's is the proper way to find out.

Of course I only can speak based on my experience. There are many different types of clutch LSD's out there and same goes with the all different versions of torque sensing differentials too.

-T

[miro-1980]

Thanks,

This is exactly what I needed to understand (and was afraid of).

Will put the Torsen in the shortest diff and try to see how it works , compared to LSD.

Once this is done I will post my experiences with the Torsen.

M

[Urbancamo]

Great Miro. I'm looking to hear the results.

Is that the same Torsen you have posted a pic somewhere in very early pages of this thread? If so, it seems to be the Torsen Type 1 with satellite gears. Same type used in some Audis etc...

T

[miro-1980]

UPDATED

Hi

I think it is the same , but I am not sure.

I cannot compare as the diff is know at the expert to see if he can fit it into my diff.

Will report progress, if any (LOL)

Miro

UPDATE:

I was told by my diff guys this can be doe and they are proceeding to install the Tor-Sen into my abarthy diff housing.

Let us see how it works when assembled ( I am scared to try !!!)

Miro

[miro-1980]

My new handbrake !

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This made me very happy camper!

Miro

[Guy Croft]

film of it in use please!!

GC

[miro-1980]

film of it in use please!!

GC

I am not quite as good as Jari-Matti Latvala just yet , but we will work on it and a film will be made to prove it !

Miro

[miro-1980]

Update : rear suspension and diff hanger mounting - reinforced

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These reinforcements are based were designed based on pictures and measurements I have taken from under a genuine gr 4 car,

In addition we were told today that our aluminum covered doors are ready.

Will post pictures as soon as available !

Miro

[miro-1980]

DOWN UNDER is where the work is...

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more to come ...

(We are still figuring out what color were the original gr 4 discs.)

Miro

[miro-1980]

Gr 4 whieldshield and rear window holders

Done a little research on gr 4 window holders.

It looks like all gr 4 ex factory cars has same front window holders one in each corners. They seem to be made of steel sheet molded to be riveted on the outside and shaped to hold the rubber seal on the inside.

The laminated glass windshield is quite stiff enough and if it is displaced - it if forced out of the chassis window steel frame on one of the corners. Thus the holders in each corner seems sufficient to hold it in place for rally use.

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Some of the original cars had the parts of the holders riveted to the chassis were painted t the bodu color , and thus were often not well visible form a distance ( i.e Walther Rohrl's car in RMC )

It seems that the diesel from London - Sidney rally seemed to have a more "panzer" version of the holders. Maybe because the windshield seal was a standard 131 S seal with chrome molding.

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As regards rear windshield holders it seems few cars had any visible holders.

Reviewing hundreds of historic pictures of original gr 4 cars I have found few showing the cars from the rear, thus there seems little evidence the rear window had extra holders. However there is good reason for a prespelex (plexiglass) window - which bends more easily than glass - is susceptible to being pushed out of the chassis window frame. This can be done by mare air pressure build up in the cockpit. Such non glass window is most susceptible to being pushed out along horizontal and vertical axis. The examples I have found seem to confirm this:

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I think we are going to use the corner holders for the front and side holders for the rear.

We will see how it works ...


Miro

[miro-1980]

HOLDERS UPDATE,

Upon close analysis I have to enter minor corrections .

The two arms of the holder seem to be different length. The cut to fit the rain rim is positioned on the short arm of the top holders:

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As regards rear holders , I am not sure they were actually installed in gr.4 cars. The ones I have seen are of questionable originality. so I think that unless I become convinced they were actually installed in gr 4 cars I will skip it for the time being.

Miro