Diff ratio?

[Jeo]

Auto NA6 originally, V-Special. By all accounts this should be a factory viscous diff, so it should be a 4.3 final drive ratio right?

The factory viscous is now somewhat worn out and effectivley open, so I'm after a functioning LSD. The car is mostly used for motokhanas and the occasional track day.

Some questions though...
The car also now has an 1800 engine, so if I wanted to keep the factory ratio to match the engine I should be looking for a 4.1?
However I also rarely hit the limiter in first during motorkhanas (want to say twice, ever) so I should stick with what I know works? Changing to a 4.1 would result in a higher top speed (which I don't think I need) at the price of acceleration, right?

Thoughts?
Do I look for one of the illusive NB6 torsens and associated tail/half shafts?
Suck it up and grab the far more common 4.1 torsen?
Find an aftermarket centre and retain my current pinion/associated 1600 sized parts?

[beavis]

Do you highway drive much?
If not, 4.3 without a doubt.

[hks_kansei]

Just so you know, the NB6 diff and the NB8 diff were the same.

Sizing, housing, centres, crown and pinion.

I can't confirm the ratios, but pretty sure they were a 4.1 like the NB8.



My car has an NB6 housing with a Torsen2 from an unknown car, and a 4.1 crown and pinion.

But yeah, there's no benefit or detriment to an NB6 diff so don't specifically hunt for one.

Be cheaper to just buy a replacement crown and pinion for whatever diff you get.

[sailaholic]

All jap 5 speeds were 4.3, including the nb6. I just went from a 4.1 to a 4.3 on my na8 and very happy with the change.
4.3s are easy to find automotive plus has plenty, they're just more expensive then a 4.1.

The na6 diff will always be a liability, so aftermarket internals would want to be cheap,

[greenMachine]

Have you tried changing the diff fluid? Those diffs are very sensitive to the condition of the oil, and it may be a quick/short term fix ...

[sailaholic]

I didn't know the Silicon fluid was changeable easily in the diff centre?

[beavis]

I didn't know the Silicon fluid was changeable easily in the diff centre?

the VLSD fluid is not a service item.
throw your girl diff away and get a man diff.

[Jeo]

Everything I had read on the subject said the VLSD's weren't servicable?

There was an NB that came with the larger housing but a 4.3 ratio. I thought it was the NB6 but really whatever gets the result is good. The half/drive shafts, housing, etc were the same between all the NA8's and 5 speed NB's as far as I knew.

If I was to get a complete 4.1, anyone know where the would 4.3 ratio come from? I'd need a shop to swap the crown and pinion over or is that a DIY job?

Not much highway driving apart from the occasional trip to Wakefield.

[manga_blue]

For motorkhanas how about a 4.7 Kia crown and pinion in a BP housing?

[slug_dub]

1.6 or 1.8... 4.3 or greater or you are doing MX5 wrong

I have a girl diff though *sniff*

[speed]

My girl diff goes with my girls car.


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[sailaholic]

There was an NB that came with the larger housing but a 4.3 ratio. I thought it was the NB6 but really whatever gets the result is good.

All jap 5 speeds were 4.3, including the nb6.

My understanding is the 6" diff wasn't used after the na6 at all.

The half/drive shafts, housing, etc were the same between all the NA8's and 5 speed NB's as far as I knew.

Not quite, the late na8s (apparently) and all nbs ran the one piece axles that coincided with the introduction of the T2 torsen. rather then the two piece unit used in early na8s. Axles for any 7" mx5 diff are interchangeable EXCEPT the SE diff and axles which were never 4.3.

If I was to get a complete 4.1, anyone know where the would 4.3 ratio come from?

All jap 5 speeds were 4.3, including the nb6.

[hks_kansei]

Not quite, the late na8s (apparently) and all nbs ran the one piece axles that coincided with the introduction of the T2 torsen. rather then the two piece unit used in early na8s. Axles for any 7" mx5 diff are interchangeable EXCEPT the SE diff and axles which were never 4.3.

Correct, but as far as function goes they are the same.
ie: you can put the NB 1 piece shafts into an NA8 diff, and the NA8 2 piece ones into an NB diff.

Personally I would recommend the NA8 ones as they are simpler to install because you can install each half separately then do up the flanges last.
Where the NB ones, being one piece, you need to put them into the diff, then juggle the whole lot up and into the car and hubs.



SE diff used the same crown and pinion to my knowledge (sizing and fitment, not necessarily ratio), the difference was the diff centre, which used larger diameter axles.




The Japanese models of the NB may well have had different ratios available than the rest of the world, they may have had a 4.3 available in the 7inch crown.

Regardless, i'm pretty sure crown and pinion sets can still be purchased brand new from Mazda Motorsports.
Mazdaspeed also used to make them, I think their catalogue listed ratios available from a really short 5.1 up to I think a 3.2 (don't quote me, been ages since I dug out the old catalogue)

If I rarely did highway trips I'd have gone for a 4.7 when I had my diff put together. Since I do a few longer trips I went for the 4.1 as a middle ground. (plus, I was happy with that ratio on the open diff)

[manga_blue]

For motorkhanas how about a 4.7 Kia crown and pinion in a BP housing?

Like this one ... viewtopic.php?f=44&t=67177

[PeterB]

Joe

I picked up a 4.3:1 NB Torsen 2 from Mania with tailshaft and one piece axles a year or two ago. Supposedly imported from a jap spec NB auto.

They do pop up for sale from time to time.

Was in Britney and is now in the NB8A. I upgraded Britney as I exploded a NA6 viscous diff at the hillclimb in Britney.

Fanta ran a NA6 diff with a mazdaspeed clutch style lsd (installed into the stock NA6 diff by Reliance), a lovely diff and survived several years of competition, but probably no longer available.