LSDs - are they worth it?

[JSE]

Hi, am considering putting a Mazdaspeed LSD in my car soon'ish (because it will get boosted eventually). However Im just wanting to know what the pros and cons are of LSDs. I have no idea about them. My car is a NA6. How will it affect the cars handling, driveability, acceleration, decelaration and handling?

[Babalouie]

Wow...lot of questions in one go Ok here goes:

Firstly the most obvious thing is that there is no more inside wheelspin (one tyre fire) and when you boot it out of a corner, there is a real sense of the back end just generating huge traction and away you go.

What's less obvious is the effect is has on handling. The tight diff will have a stabilising effect on the car, so lift off throttle and midcorner corrections will seem damped. But, the price is, it can feel like the car is a bit less eager to turn in and can feel more understeery, but most ppl just drive thru this by simply being more aggressive with wheel and pedals. But it means that at 5/10ths it can feel more leaden and pushy.

Other downside is that until you get used to it, the line between slip and grip can seem really fine. Especially in the wet, once the back end lets go, it will spin 360 with relatively little throttle. So once past the point of no return it is less forgiving than an open diff. The price is simply that ou have to become a better driver and it really teaches you the importance of throttle control.

In terms of driveability, a Mazdaspeed is an excellent choice since it has very little compromise. In fact it's largely the same in feel to the oem torsen rather than an aftermarket unit (that said, it is excellent). But a really tight brand of diff, like say Cusco RS, will really lock up brutally, and everything will be exagerrated. You will feel the lsd lock up and around the corner feel the engine have to fight against its resistance. If you are caught off guard, the understeer will be huge, and tight corners and u-turns will lock up the lsd, causing the axles to wind up and make all kinds of funny painful noises and make the car hop and strain.

[StanTheMan]

Well......Its the 1 best single mod i've done to my car. It still puts a big grin on my dial when i can feel it lock. I love it.
In hind sight it probably made all the suspension mods bracing & tyres work together in a way they should. The car is a different car to drive after the modification.
as far as locking up is concerned....in a standard 1.6 its only dangerous when you have seriously bad tyres or its very slippery. with good tyres i found once i actually managed to loose traction on a tight U turn is a case of simply backing off. & the tyres would find thier grip .....very easily controlled. You need to seriously be doing something really stupid for it to catch you out.
In a case of a turbo.....thats obviously a different storie & i can't comment as i havent done that much driving with a Turbo fitted wit an LSD.

as far as going Turbo....Id also seiously consider doing a 1.8 upgrade. also change the ratio to at least a 4.1 so you don't run out of RPM before you have to change gear too quickly (I hope that makes sense.)

4.1 as opposed to 4.3 in my almost Stock 1.6 has made very little difference. My 1.6 with timing advance CAI and AFM spring adjustment still accelerates quicker stan a stock standard 1.6.

You will find at around 4000 rpm mark it has slightly less go than a 4.3 ratio on the same non turbo car.

Handleing......i cant see it being a diadvantage in any way. it will only compliment a good suspension & tyre set up.

Also my experience is with a Torsen ....not a Mazspeed LSD. keep that in mind also.

[nath]

An LSD is going to be my next mod.

I know babs touched on it breifly, but what is the main difference between a Mazdaspeed LSD and a Torsen?

And which one would be more recommended for my NA6?

Cheers,

Nath

[slammer]

The Mazdaspeed is a great choice, really helps put the power down exiting corners. PM me if you are looking for one

[JSE]

Yeah I would also like to know the difference between the Mazdaspeed and the Torsen

[Babalouie]

Yeah I would also like to know the difference between the Mazdaspeed and the Torsen

Mazdaspeed, KAAZ, Cusco, et al are all mechanical, clutch-type LSDs. They work on a completely different principle to a torsen.

In a nutshell, someone worked out a long time ago that when the inside wheel spins in an open diff, the internal gears are forced apart. Clutch-type LSD harness this force to stop the wheelspin by inserting clutch plates beside the internal gears. The more wheelspin, the more the gears force against the clutches, and since the "other side" of the clutches are presed against a common housing, the clutch friction forces the gears to spin in the same direction, hence quelling the one-tyre-fire.

The problem is, this phenomenon isn't that strong. So the clutches need some spring preload assistance to get any meaningful amount of grip. Hence the downfall of the clutch-type LSD, it only has a narrow operating range. Set it up to be super tight on the track, and it will never fully unlock for parking and town driving. Set it up so that it's nice and loose for crawling, and it'll never lock up enough on the track to fully stop the wheelspin. Hence some factory LSDs like say the one that Commodores come with, still allow a lot of inside rear wheelspin. And hence a Cusco RS is a pain on the street. So the trick with a clutch-LSD is to pick a brand which you know has the right compromise for you

So because of the inherent limitations of the clutch-LSD, someone invented the torsen. A torsen relies on a totally different set of rules, and there are lots of planetary helical gears around the circumference of the diff, like so:
http://i106.photobucket.com/albums/m255 ... /Diff4.jpg

When the car goes around a corner, the outside wheels scribe a wider arc, and travels a further distance. The torsen uses this differential in axle speed to apportion torque. Depending on the type of torsen and the design, usually the outside wheel gets 1.5 times more torque than the inside wheel. So rather than try to quell wheelspin by equalising the axles, the torsen tries to be intelligent. Downside of the torsen is that sometimes it's wrong-footed, and can default to spinning up the inside wheel. That said, the oem Mazda torsen really is excellent, and the design of the MX5 rear suspension makes the most out of it to the point where it works perfectly 95% of the time, and it works much better than say, the torsen in the S15 Silvia.

But for a high-power application, the torsen can sometimes be confused, since both wheels can wheelspin and hence it's hard for the torsen to figure out exactly which one is the outside wheel. So for a turbo application that sees the track, go clutch-LSD of a good brand. For NA applications, the oem torsen is really very good. The benefit of the torsen is that it doesn't try to lock up when you don't want it to, and hence has a free-er, more agile turn-in. A decently tight clutch LSD will have that slightly understeery feeling like I said in my original post. The reason for the slightly leaden feel a clutch LSD can have is because it isn't intelligent, and will try to lock up whenever it senses a difference in rotational speed between the axles. And that includes braking into a corner, coasting around a sweeper, etc. So it'll lock up and do its thing in situations where you don't really need it to.

The other upside of the torsen is that it never wears out, whereas a clutch LSD eventually will wear out the clutch plates (which also lose their spring tension eventually) and will have to be overhauled with new parts. Also a clutch LSD will have to be re-shimmed every say 20,000kms to maintain spring tension and performance. When a clutch LSD is all worn out (50, maybe 80,000kms) it's basically just an open diff again.

...so there you go

[rodent]

...and this guy makes a living as an accountant!

But then what about VLSDs Babs..?

[JSE]

Thanks for the essay babs. Really helpful to not only myself but I'm sure alot of others viewing this thread. Looks like next on the to-do list is swap my diff for a Torsen.

[Babalouie]

:roll:
...and this guy makes a living as an accountant!

Hey, don't judge a book by its cover...CT is a beancouner too

But then what about VLSDs Babs..?

VLSDs are a pretty el-cheapo concept that doesn't really work very well.

Imagine if both axles have a series of circular plates at each end. The plates have vanes cut into them, and the whole thing is encased in this special jelly. As one wheel spins up more than the other, its vanes will spin faster than the other set. Hence the jelly gets chopped up. But the chemical makeup of the jelly is such that the more you try to chop it up, the stiffer and thicker it gets.

Hence, in theory, it will reduce inside wheelspin, and that's the thing, by its design it can only reduce wheelspin, not eliminate it, since the jelly can thicken, but not actually solidify (which is what it will need to do to really lock up). Also a VLSD is prettu insidious in that, in order to get it transfer torque to the outside wheel, you need to apply more more, because you actually *need* the inside tyre to be wheelspinning in order to "activate" the jelly. So to drive a VLSD equipped car, to maximise power to the outside wheel you have to floor it and exit the corner with the inside wheel well and truly wreathed in smoke. Which destabilises the back end, and means taht you have to be quite ham-footed to actually do any throttle steering.

The benefit of the VLSD is that it's very very progressive, and will never lock up to the point where an average person with no throttle control will really get into trouble. But for a performance application, chuck them in the bin In the UK, there are motorsport places that can pump in a thicker grade of jelly under extreme pressure, and apparently that works well, but in Oz the only thing you can to to upgrade a VLSD is to put shims inside to introduce an element of friction. This is kinda dodgy tho and has a short lived effect.