4.3 vs 4.1 with 5spd

[goonie]

Hi Everyone,

I've got an NA6 (turboed with approx 125rwkw) with stock VLSD diff (4.3?).

Looking at finally getting a Torsen but can't decide on a 4.1 or a 4.3.

I've always had the 4.3 so I'm used to that. The few extra km's gained from a 4.1 at top end shouldn't matter much as car is street dríven and hardly redlined (though that might change knowing I won't blow my diff now).

Was initially looking for 4.3 but have read that a lot of people with turbos favour the 4.1 (4.1 seems to be cheaper too)?

Also, is the T2 worth getting over a T1? More for the strength aspect rather than LSD performance.

Cheers

[hks_kansei]

Total difference will be about 4.65% taller with the 4.1 vs the 4.3

So at a given RPM in each gear expect to be travelling 4.65% faster, or expect roughly 4.65% slower acceleration (really rough there, since it doesnt take ANY other accel factors into account)

4.1 is a lot easier to find, being the OEM ratio for the NB8A (non-10ae)
4.3 is somewhat harder, since I don't believe it was fitted to many 1.8 diffs from the factory (not in Aust at least)


As for the diff centre, as well as being stronger, the T2 is also much easier to find than the T1.
The T1 was used in the NA8 Clubman only. Where the T2 was available as an option in basically every NB (overseas at least, not sure is Aust got the option)

Bear in mind the LSD in the Turbo SE is similar to a T2, but not the same. It's a different kind again, which also uses thicker half shafts with a different spline count to a regular NA8/NB diff.




edit:
worth adding, in case you dont know, that a torsen will not fit into an NA6 diff housing, as the Torsens were made for the NA8 and later cars which had a larger housing. The crown and pinion of an NA6 diff will not fit a 1.8 sized centre either.

[Nevyn72]

Bear in mind the LSD in the Turbo SE is similar to a T2, but not the same. It's a different kind again, which also uses thicker half shafts with a different spline count to a regular NA8/NB diff.

After doing a lot of research I found that the SE diff is actually a true Torsen T2 but different to the ones found on other MX5's.
It's actually the same unit as the one used on a Honda S2000, hence the different half shafts.

Later model MXs, NC & ND get the T2 'like' centre.

[hks_kansei]

That would be it, I remembered that the SE one was similar, but different to a regular Torsen2.
I thought there was also some other design difference than the shafts?


The NC unit, from my memory chatting with the guy that built my diff (few years ago) isn't a Torsen style unit.
From memory it's essentially an open diff with little clutches that grab during side loads of the side gears.

I may be mistaken though, it's been a few years since I had that discussion about the LSD.

[Nevyn72]

That would be it, I remembered that the SE one was similar, but different to a regular Torsen2.
I thought there was also some other design difference than the shafts?

Yep, it also uses a different type of uni-joint on the half shafts, I can't remember what they are called but were popular in racing circles at the time.

The NC & ND use a Tochigi Fuji Super LSD.
Here's the ultimate guide to MX5 differentials!
http://www.miata.net/garage/diffguide/index.html

[speed]

4.1 will hold gears longer and your turbo anyways, so 4.1