sup3rbad

how does this torque sensing lsd work and is it good for drifting? if not what are some good lsds?

VividRacing.com

Cusco is working on an LSD and it should be available soon.

eccles

Google is your friend. http://www.torsen.com/general/general_faq.htm

syntrix

Further reading on the different types of diffs (ie, 1 way 1.5 way, 2 way)

http://www.club4ag.com/faq%20and%20t...ential_101.htm

P00Man

i think the RX-8's LSD is a Tochigi - Fuji unit
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eccles

Yes, it comes from a different manufacturer, but it's still a TORque SENsing unit, functionally similar to the TORSEN. Torsen tries to prevent its trade name being used as the generic descriptor for this type of diff, to prevent it falling into general usage and thus being useless as a trademark, such as Aspirin and Escalator have become.

PUR NRG

Just to throw a monkey wrench into things, there are also Automatic Torque Bias Differentials like quaife http://www.quaifeamerica.com/
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eccles

I think you'll find that the Quaife unit is also a Torsen-style unit. The description of its operation is the same, and the cutaway diagram shows it uses a worm gear arrangement similar to every other torque sensing unit.

Psylence

Quaifes are awesome! Lifetime warranty, bulletproof. I have 2 in my Subau

PUR NRG

There are two major differences. Pro: no clutch plates to wear out or service. Con: if one wheel lifts off the ground, it immediately acts like an open diff. I think the con is negligible and really like the "no servicing" part. Remember the first initial in "LSD" is lmiited--after a certian point the inside wheel will start to spin. The Quaife doesn't do that. Also based on the previous explanation of 1-way vs. 2-way LSD, I believe because the Quaife is completely gear driven it acts like a 2-way. Here's some more info on various differentials:

Limited Slip Differential
This is basically a device fitted in place of the standard diff and it allows the wheels to have a small difference in speed but will not increase this difference even if one of the wheels has lost traction and wants to spin faster. In plain English this means that your vehicle will be able to negotiate corners on tarmac as normal, but if you were to lose traction off road, instead of one wheel spinning uselessly and the other staying still, both wheels would turn at a similar speed propelling the vehicle forward. LSDs (Limited Slip Diffs) are available for many vehicles from quad bikes through to Toyota and other Japanese four wheel drives.

Viscous Control Units
VCUs are very similar in operation to the LSD above. Originally developed by the great engineer Harry Ferguson, of Massey Ferguson tractor fame, they have found their most common home replacing the centre diff lock in Range Rovers since 1989.

The VCU works by letting a certain amount of movement occur between the wheels (for cornering etc.) but if this is exceeded the device locks up solid like a diff lock. Essentially this system works well but many people have found, particularly at low speeds, the device gets confused and doesn't always lock up properly. However on the plus side it requires zero operator input.

Quaife Diffs
It is very difficult to explain how the Quaife diff works, quite simply because even the inventor Ron Quaife, claims to not understand it exactly just that "?it works and that's all that really matters". The best description for them is a torque biasing differential. This means that it distributes the torque, or twisting motion, to the wheel that needs it but no more than it needs. Their effect is most noticeable at speed which has resulted in their fitment into many of the cars on the Dakar rally as well as in many conventional rally cars. I personally have had them fitted front and back in my own Defender 90 for over two years and now swear by them. My own opinion is similar to that of Mr. Quaife's; they work. Occasionally it has been necessary at slow speeds to dab the brake pedal to set up the torque reaction and get them to work particularly when horribly cross-axled. In one instance we were in a situation with two opposing wheels high on rocks and the other two floating in mid air an not moving forward. In a normal car this would have resulted in a need for a tow, but by simply engaging a low gear and dabbing the brake pedal the car moved ever so gently forward and back on to the level. What more do you want?

Lockright
The Lockright was originally conceived for the US military and utilises space age materials but has recently found its niche market in Australia. The unit works on a completely different concept to all the other devices. The unit that replaces the centre of a conventional diff is permanently locked. However when it comes to negotiating corners the outside wheel is allowed to rotate faster. This means it will corner effectively on tarmac, but in off road conditions no wheel is allowed to rotate slower than it's driven speed. The only disadvantage with the system is that at present it does not like permanent four wheel drive systems (e.g. current Land Rover products) for road usage.
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Gord96BRG

The RX-8 Tochigi-Fuji torsen-type unit is pre-loaded, so it doesn't suffer from the zero traction problem that no-load Torsen units do (like those used in the 94-02 Miata, for example). The Quaife could also be another example of a pre-loaded torsen type.

Regards,
Gordon

sup3rbad

so which of them would be good for drifting?

wakeech

a solid (fully locked) rear axle is probably best for drifting, to keep both wheels spinning equally.

rxphink

Can someone help me out here, is a Torsen diff a helical diff?

If so then the Diff in the RX-8 is not a torsen.

From the pics I've seen it looks more like a phantom grip stlye of diff. HD Spring pressing the gears against the housing to create the lockup effect.

It could very well be that the cutaways I have seen do not show the inner gears though.

Efini 8

CUSCO's RX-7 LSD is compatible with the RX-8 FYI. If companies do come out with an LSD, 1.5 way will most likely be the choice.

Gord96BRG

Not sure what you mean - all diffs use helical-cut gears. The RX-8 diff is definitely a Torsen style, with helical-cut worm gears.

Regards,
Gordon

rxphink

My understanding of a helical diff is a diff with a worm gear center.

The pics of the RX-8's diff show it to have a spring in it's center. with crown gears along the perimiter of the housing

eccles

The RX-8's diff certainly is a torque-sensing unit, but it has a lower TBR (torque bias ratio) than that fitted to the late RX-7's.

The FD's TBR was 2.8, while the RX-8's is only 2.0. This means that the 8's diff will send up to 2/3 of the available torque to the wheel with the greater traction, while the FD's could transmit nearly 3/4 to that wheel. While a higher TBR is useful in spirited and competition driving, a higher TBR makes the diff's action more intrusive. I guess the lower TBR was yet another compromise towards everyday civility in the RX-8's design spec.

yves

If LSD is such a great thing, why does Mazda even offer the automatic without it? Don't they feel bad about that? Frankly, I wish it were offerred as a separate option, rather than as part of the "sport package".

darkducati

I think it's because people who are interested in performance aren't going to buy an auto. Now if you'll excuse me, I am going to go put on my nomex.

NAVILESRX8

iTrader: (1)

The OE Torsen LSD in our RX8's is plenty fine for drifting. I wouldn't go with a more expensive clutch type(Cusco or KAAZ) until you are making big power and have a crazy suspension...


Aftermarket LSD's are recommended in the AE86 world, because most of the OE LSD's were marginal and 15-20 years of wear and tear just wear them out. Brand new OE LSD's are hard to find and expensive, it just makes sense to get a stronger aftermarket LSD. I never had any aftermarket units in my AE86's...I was lucky enough to find really tight low mileage units that worked flawlessly.

And those Viscous type LSD's...they suck.

wakeech

...they work well in the right application (such as a centre differential in an AWD system).

NAVILESRX8

iTrader: (1)

You are correct...they work good in the center....

Gord96BRG

What darkducati said - a Torsen diff only makes a difference in at-the-limit handling, ie at the limits of the performance envelope. The performance envelope is much smaller in the Auto RX-8 (well, at least in the acceleration direction), so Mazda figures that buyers of the Auto are less interested in maximizing performance.

FWIW, for the entire time that a Torsen LSD has been available on the Miata (since 1994), the auto cars have never had it available. Ie, if the Torsen was standard on the Leather Package - it was only the manual trans LPs, not the auto trans LP.

Regards,
Gordon

GeorgeH

iTrader: (2)

One more bit of information I'll toss in here - Torsen type units are quite bullet proof, with one exception as I understand it. They really do not like wheel hop during drag racing. They can take lots of torque if you keep the wheels on the ground, but when the wheels start hopping the impact loads can be very damaging to a Torsen.

I've picked this bit of information up by following the forced induction Miata crowd. If it's not true then somebody please chime in with other information. But, as I understand it, you should be carefull if you are into drag racing your '8. Too much wheel hop could result in a catastrophic failure of the diff. Yes, the transmission does seem to be the weak link for now, but I'd be carefull with the diff just the same.

George