Limited Slip Diff for '98 NB8A

[Josh2232]

Hi everyone,
i'm fairly new to the scene and have only had my NB for about 6 months, i have a bit of mechanical knowledge but not a heap. I've already done coilovers and some other light modifications but i'm thinking that it may be beneficial to get an LSD. I was wondering what would be easiest / more cost effective:
-either buying an insert (in this case which type and from where), or
-buying a used LSD from an NB8B (if thats possible) and fitting that.

I don't really know heaps about which types of LSD's will be compatible or what the best way to go would be so hopefully you guys (and girls) can help me out a bit from your own personal experience!

-Josh

[BadBong]

Hey Josh, I've just had my LSD installed a week ago so I've got all the answers for you:

Is it worth it?

HELL YEAH?! It's a totally different car. I can still drive it the old way but now there's another level of challenge to overcome - learning to use the throttle to control turning angle... and it's just fantastic. It also rewards you for accelerating out of a corner (and indirectly forcing you to learn the 'slow in, fast out' approach)

What is the cheapest option?

Well, it's all around the same if you're going to get a mechanic to do the job... here's a summary of my research:

1) If you just get the insert without any housing, you can probably get it for $400. But it'll take about 6 hours of labour to uninstall, assemble and reinstall;
2) If you get the centre housing, you can probably get it for around $600. It should only take about 4 hours of labour;
3) If you get the whole centre with control arms, it'll cost you around $800 but it will only take 2 hours of labour;

*Note that these prices are based on a Torsen2 LSD. Other more track oriented LSDs will be alot more expensive (just do a search on eBay);

As you can see... it's much the same to be honest. My view is that if you can source a whole centre with control arms WITH warranty then that's the go. It'll also give you the option to sell your existing diff as a complete package.

I personally went with option 2 and got the centre from MX5Plus in QLD. Comes with a year's warranty.

*Note - you might want to do some research on the diff ratio. I think the NB8A comes with higher ratio (i.e. faster acceleration but shorter gears) so you might want to think twice about getting one that is lower ratio...

Good luck ;)

[hks_kansei]

NB8A Diff ratio is 4.1 for Aussie cars.

Also, not sure what you mean by control arms with the diff? The control arms have nothing to do with it.
Do you mean Half Shafts? (The axles that come from teh diff and go to the hubs?)

[Josh2232]

Thanks for your replies guys! So Vic, if i got this http://mx5plus.com.au/part_display.php?part=73&cat=11 a Torsen 1 Centre with a 4.1 ratio it'd be the right one for the job?

I'm not exactly sure of the difference between torsen 1 and 2 in real world terms and driveability so my next question would be, is it better to continue searching around for a Torsen 2 with the 4.1 ratio, just get the Torsen 1 listed above, or go for a different ratio?

If i went for a 4.3 what impact would that have on the car? just acceleration or would it rev much much higher in 5th?

sorry for acting like such a rookie

[BadBong]

Thanks for your replies guys! So Vic, if i got this http://mx5plus.com.au/part_display.php?part=73&cat=11 a Torsen 1 Centre with a 4.1 ratio it'd be the right one for the job?

I'm not exactly sure of the difference between torsen 1 and 2 in real world terms and driveability so my next question would be, is it better to continue searching around for a Torsen 2 with the 4.1 ratio, just get the Torsen 1 listed above, or go for a different ratio?

If i went for a 4.3 what impact would that have on the car? just acceleration or would it rev much much higher in 5th?

sorry for acting like such a rookie

Well, you'll have to do your own research on this one mate.

I went with a T2 > T1 based on its characteristics and I believe T2 suits my style of driving more.

As for 4.3 ratio... I think you'll definitely have to do the maths on that one. 4.3 in a 5 speed during peak hour city driving can be quite frustrating I would think.

NB8A Diff ratio is 4.1 for Aussie cars.

Also, not sure what you mean by control arms with the diff? The control arms have nothing to do with it.
Do you mean Half Shafts? (The axles that come from teh diff and go to the hubs?)

You're right mate - I meant Half Shafts.

[hks_kansei]

T1 I think has a slightly higher torque bias.

But, the T2 is a stronger diff, and a better design (T2 can be rebuilt and shimmed if you want it tighter, T1 can't be shimmed)

[BadBong]

T1 I think has a slightly higher torque bias.

But, the T2 is a stronger diff, and a better design (T2 can be rebuilt and shimmed if you want it tighter, T1 can't be shimmed)

That's correct - I went with the T2 based on the fact that my car's turbo. I also read somewhere that the way that the T1 and T2 locks up is different and T2 suited my style of driving more - do a quick search mate ;)

[hks_kansei]

The way I look at it is that the Torsen is a really good option for a road car, you get the extra grip out of the corners, but don't have to live with the clunking, chirping and chattering of a clutch-pack diff.

However, the clutch pack diff is a much better choice for if you want to drift.


Basically, they both give extra grip out of corners, they just do it different ways.

A clutch pack one will lock both wheels together under power (and under decelleration it it's a 2 way) so that when the left wheel spins at X, so will the right one.... regardless of if the car is going straight, sideways, or even if a wheel is in the air.
Both wheels get even torque/power 50% each.

A Torsen allows the wheels to spin at different speeds, but the gears inside mean that as one wheel loses grip the torque is multiplied and sent to the opposite wheel. Say a torsen has a Bias of 4:1, the inside wheel spins, it will multiply the torque it's receiveing by 4 and send it to the other wheel, so you end up with the outside wheel getting 80% of the torque, and the inside getting 20% (of course, this relys on some strain, so if the inside wheel has no grip at all, say it's airborne, or on ice, it will spin up and get 100% of the torque as 4x0=0...... bear in mind, shimming a T2 will ad preload so it's always under a little load)

For reference, an open diff does the opposite of a Torsen, the power is sent to the wheel with least resistance. so when one slips, all the power goes there, and you end up with grippy wheel getting minimal power, the slipping wheel getting 100%.



I hope my explanations are good. They're how I understand each diff to work, so if I've got anything wrong please correct me.

The best resource for info is to do some googling, read up on Wikipedia, Howstuffworks, google, etc about the 2 diffs and their characteristics.

[OurCognitiveSurplus]

Hi, good thread, I've been wondering the same sorts of things about my NB8A and haven't been able to find much useful information.

If I'm right, the NB8A comes with 4.1 open diff. I don't know what the NB8B comes with.

Another issue I'm wondering about is the impact of a diff on classifications for various forms of racing. As far as I can see, the rules for my local hill climb do not refer to diffs at all. So I'm not sure if diff changes are fair game, or if they'd out you straight into the most modified class with the serious race cars - which would be a problem.

[hks_kansei]

Yes, Australian NB8As came with a 4.1 ratio and an open diff. (No idea what ratio other countries got)

Of course, the 10AE and the Heritage editions had different diffs (10ae had Torsen, Heritage, unsure), and being 6 speed I think also a different ratio? (unsure)

[BadBong]

ADM NB8Bs come with 3.6 or 3.7 open diff.

Kansei - what's shimming...?

[hks_kansei]

Basically The T2 has small conical washers in it that press the side gears apart and onto some friction things. (I wasn't 100% certain how it worked when it was explained to me)

They can be replaced, or have more washers (shims) put in to make it stiffer and a bit more like a locked diff.


A brand new Torsen will feel quite stiff and can sometimes chirp the inside wheel in carparks, an older one will be looser and not (as the washers have lost some of their springyness and aren't pressing as hard)



Mine hasn't been shimmed, but it's also fairly new so it's a bit stiff still. (I think the centre only had 50,000km on it or something? I know the crown and pinion on it only had about 2,000km on them)

[OurCognitiveSurplus]

Can these inserts go into any of the mx5 open diffs, or does the insert need to be matched to the ratio (i.e. is an insert for a 3.9 diff different to an insert for a 4.1)?

http://mx5plus.com.au/part_display.php?part=70&cat=11

[hks_kansei]

Can these inserts go into any of the mx5 open diffs, or does the insert need to be matched to the ratio (i.e. is an insert for a 3.9 diff different to an insert for a 4.1)?

http://mx5plus.com.au/part_display.php?part=70&cat=11

The centre (Insert) is the same, you can use any ratio, or re-use the original one from your car. (note, the crown wheel and the pinion (bits that determine ratio) are a matched set, so you can't use a 4.1 pinion with a 3.6 crown.... it will chew itself to bits very quickly)


The only freak is the NA6, which had a smaller diff altogether which means you need to replace the housing/driveshafts/centres with ones from an NA8 or an NB

[hks_kansei]

Here's an exploded view on one that looks very similar to an MX5 diff:



The bit piece near label F is teh centre/insert.
The ring to the right of it is teh Crown wheel.
The long geared piece near C is the pinion (attaches to the tailshaft, which attaches to the gearbox)