Torsen limited slip
 

Not sure if this subject has been talked about, but as you know the BRZ comes with a Torsen LS diff. Should be a much better unit than the typical clutch pack type LS. I'm not fully versed on the operational differences between the two types of Limited slip's, perhaps others with a better knowledge of these two could chime in.

I know the clutch pack types seem to have limited life and require special lubes.

http://auto.howstuffworks.com/differential6.htm

My Boss comes with a Torsen differential as well. :D

if you do not know, then do not make such statements as "should be much better."

to limit slip, a limited slip differential has an internal mechanism that uses pressure in one form or another to force the slipping wheel to keep on turning.

torsen is a self contained unit and needs no replacement, however it CAN wear out if you overpower it. Just like everything else! However, it is non adjustable, so you can't upgrade it to handle more power or change its engagement and disengagement characteristics.

clutch packs also come in many different forms, OEM is one thing, after market clutch packs of 1.0, 1.5 and 2.0 slip variety are an entirely differnt ball game

to say they don't last is to say that the clutch in your car doesnt last, so you should buy an automatic. If you add a turbo kit and do hard launches for days on end, you'll fry your clutch. That's not the clutch's fault, that's your own foolishness.

same goes for clutch type lsd's.

A clutchpack type LSD has a faster and more predictable lockup. They do need friction modifiers in the oil, and occasional rebuilding if you race or abuse them. But, they can be adjusted for lockup speed and force, as well as the ability to do so separately for on- or off-throttle behavior. Clutchpack LSDs are preferable for any form of racing.

Torsen (TORque-SENsing) LSDs are simpler in that they have a set lockup speed and force. However, they are dependant on the slipping tire to have SOME grip. If the slipping tire has no grip at all (i.e. it's in the air) the torsen will not lock and will act like an open diff. So they are not the choice for off-road or competition where the car may lift a wheel. However, the nice thing, as stated above, is that they never need a rebuild and can work just fine in straight gear oil.

So while the torsen LSD will work perfectly fine for the vast majority of FT owners, an upgrade to a clutchpack type LSD will be a popular mod for racers looking for 10ths.

I tend to agree with you that the torsen units are better than clutch packs. Both have their ups and downs but a properly tuned setup can make great use of a torsen diff.

The primary difference between the two is that at a clutch type differential locks the rear wheels together and delivers an amount of power to the wheel with traction based on the breakaway torque of the clutch pack. In a torsen diff on the other hand, as torque between the two wheels becomes uneven the diff mechanically provides more torque to the wheel with more traction, and thus more potential to use the increased torque delivered to it. How much torque it can transfer to one side is dependant on the torque transfer ratio built into the differential.

The downside of the clutch pack is along the lines of what you said. The clutch plates in the differential are a wear item and typically produce quite a bit of noise. The operation of the differential also changes substantially as the clutch plates wear, meaning unless they are kept in top condition between heavy use (i.e. track days) their operation will become inconsistent. This has to be adjusted for in your chassis setup if you want to preserve optimum performance meaning clutch diffs require a lot of maintanence to remain competitive. They're also reputed to have inconsistent or on-off-like engagement although this is generally only a problem in cheap or poorly tuned clutch diffs. In a decent setup lock up is very smooth and predictable.

Torsen diffs, unlike clutch packs, are virtually silent and require no maintanence making them ideal for OEM applications. The biggest drawback to them is they're generally more expensive than a clutch pack and, like an open differential, if one of the wheels loses contact with the road the diff will route all of the power to that wheel. In other words if you lift a tire you can't put any power at all down until it comes back into contact with the road. Some torsen type diffs now use a preload spring (like clutch diffs do to combat the same problem) to allow the diff to keep some power to the wheel with traction in the event a tire is lifted but I don't know if this is the case with the one in the BRZ. However, with proper chassis and suspension tuning you ideally shouldn't be lifting wheels anyway.

Here is a good link for further reading: http://www.taylor-race.com/pdf/under...ferentials.pdf

Not sure if I mentioned it before, but awesome car choice :thumbup:

If I weren't looking for a DD replacement (and didn't have a track car already) I'd have a Boss LS sitting in the garage.

Thanks!

It's a large car but I can appreciate its relative mechanical simplicity. Only a few months before track season starts up so I can't wait to get it out there.

:word: I looked into a Boss Laguna Seca too and it has massive pace and potential, but just my preference, it's too big for me. Nevertheless, a very capable car.


Back to the OT :eyebulge:

Different LSD's work best for different applications. In my experience, robust clutch-pack LSD's [i.e. OS Giken] are quickest on the track in a rear axle, however ATB's [i.e. Quaife, Torsen] are quickest on the track in a front axle.

ATB's require zero maintenance and do not change performance over time, whereas clutch-pack LSD's require a friction-modifier gear lube and the discs do wear over time. That said, the rate of disc wear is proportional to usage and individual LSD model.

In one of my MINI's [an '07 S w/factory 20% lock clutch-pack], I fried the discs in the LSD in one day at an HPDE. The diff wasn't durable enough to handle stock torque in a racetrack setting with Hoosiers. In that application, an OS Giken would've been a good clutch-pack choice, but an ATB works even better in front-drive because it distributes torque to the tire with the most grip [mechanically] and pulls the car around the corner. This of course isn't directly applicable to the BRZ, it's just perspective how there are different solutions for different applications.

I for one don't mind the car comes with an ATB. It's not "ideal" for rear drive in terms of lap-times, giving up a few tenths for reliability and consistency, but then again, this car has never been about that. It's also a plus over an open-diff. Lastly, I like the hands-off approach to maintenance.

That's my $0.02

Hey guys...thanks for all the reply's. I see that both types have their pro's and con's. I had a clutch type on my '95 E36 M3 and it was toast at about 15,000 miles.

I like that the Torsen basically won't wear out and for street use looks to be a good choice.

a Torsen will toast just as much as a clutch pack if you pound on it.

if your OEM M3 diff blew after 15000 miles then maybe it was driver error.

Torsen's don't have wear items other than gears. They'll only break if one of your drive wheels leaves the ground and you shock the assembly upon landing [i.e. keeping your foot in it]. Then again, doing that is just as much risk to axles, pigs, trans gears...everything else in the drivetrain. In your situation, the Torsen was the fuse.

Clutch-packs can be destroyed in minutes if they're ill-suited to the application...like the OEM clutch pack in the R56 MINI Cooper S in the example I gave above. They don't "blow", the discs simply slip and turn it into an open-diff.

if it's mechanical, it will break :D :D :D

I have never heard of a Torsen (or helical as they are often referred) "toasting" in any reasonable conditions, 500hp autocross on R-comps maybe, but in their intended use the units are basically indestructible.

I have a stock S15 helical LSD (torsen, whatever) in my 350whp S13 track slut and it has no issues as long as I keep both rear wheels on the ground.

Every mechanical device has a limit, you won't find the breaking point of the stock LSD portion of the Diff without R-comps or drag slicks. It is not an item of concern and is a god send for this car given how well the units works on the street, power over is predictable and smooth, there is almost no ramp to the torque vectoring, is is unimaginably smooth, even more so than the stock Viscous coupled units.

Sure, but it's less likely to break under most track conditions where you aren't shocking the unit, whereas many OEM clutch-type differentials can be fried by something as simple as repeatedly lifting an inside rear tire.

:word::word:

the boss 302 LS is a great car, if you have watched american top gear lately they put it up to the roush stage 3

the 302 is faster around the track by a few seconds, good job ford :D

i bet you like your 7500 rpm redline too :D

EDIT: by the reviews the torsen is very good anyways, im going to be using it till i need a mechanical on my track trim 86

:thumbup:

Btw- you can usually "trick" a torsen with one wheel having zero traction by light application of the brakes. Gives the free spinning tire some resistance and allows the torsen to send torque to the other wheel.

No maintenance? Don't you still have to change the oil in Torsens? Like ATF or 75W-90 gear oil?

yes. and better yet, a manufacturer can simply program this into the stability/traction control. porsche PTV is a perfect example of a mechanical LSD working in concert with active electronics.

It's a differential, hopefully you'd be changing the fluids whether it had a open diff, torsen or clutch pack.

What is this fluid changing wizardry you are referring to?

I just wait until the car tells me to add more to any of the various reservoirs just as the manufacturer intended.

see those plugs, one's to drain and one's to fill.

http://www.gotitrex.com.au/home/images/stories/r180.jpg

your sig says you drive a jeep wrangler?


see that square key plug, that's where you drain and fill your diff fluid.


http://www.wanderingtrail.com/Mechan...s/DSC04204.jpg

I thought those were just for show.

they are, you can get ionized plugs and be all baller, go dual colour even.

LOL :happy0180:

Well I know open diffs rarely ever need their oil changed. Clutch and viscous types (like mine) need them changed more often. But does anyone know how often a Torsen needs its oil changed? I'm assuming a lot less. I remember reading that the Quaife/helical front diff oil is basically good for the life of the diff. So I suppose it could be the same with a Torsen?

you guys troll but for every 1 of you there are 100 people that actually think like that.

not all viscous LSD's can have their fluids replaced, most are sealed.

at least subaru is like that, they had pre 98 subaru's had center viscous diffs that could have the fuilds replaced but they gave up on that. If you fry one now, gotta get a new one.

Oh... my rear and center viscous LSD does need to be changed though. The center shares transmission fluid and the rear uses a 90 weight gear oil.

Need and should have can be different. IIRC Hondas with Torsen's usually want 30k, maybe 45k changes. I can't recall. I change my hondas every 12-15k. IIRC (I'd have to check) the open diff/transaxle suggested intervals were the same as those with a torsen.

In a clutch type the fluid life is shortened by the shearing action that creates the force that splits torque.

In a helical or Open diff there is only heat and age related break down (heat is also considerably less since it is not a friction based torque transfer

My IS300 OEM Torsen LSD (the same one I think that's going to be in the FR-S/BRZ), is supposed to have the oil changed every 60k miles, the same as the open diff. Some people change their LSd diff oil every 30k miles.

Sweet, so what fluid does it use? Just some 75w-90 LSD gear oil?

why not get the base model with no lsd and swap in a better aftermarket one? Or is this one going to be OMG amazing or something?

Because they likely aren't going to offer one here in the US without an LSD. Not to mention, it's more money and the Torsen is more progressive and more reliable/consistant than a clutch type anyway.

Base model not sold in the USA. I know, I'm sad too.

Yeah. I just used Mobil 1 75w-90 gear oil.

Cool, that's what I use in my car now and was hoping to use in this car when needed.