Best Differential Swap

Postby **Boyracer** » Sun Feb 27, 2011 9:03 am

I had a aussie 6 speed with a 4.1 ratio, as stated by wazman first gear is useless, just get yourself a 3.9 Torsen...if you get a 4.1 you will be dissapointed.

Having said that I find my 10AE really good to drive and I would not bother changeing the final drive ratio ...I'm assuming it has a 3.6...maybe the 15 inch wheels and little tyres work a bit better than the 16s on the NB8B.

bootz · Postby **bootz** » Sun Feb 27, 2011 1:21 pm

Mazda spec sheet for Australia indicates 10AE in Australia is 3.6 (3.9 in US though):

de Bounce · Postby **de Bounce** » Sun Feb 27, 2011 5:29 pm

bootz wrote:Installed the diff yesterday. This is my reaction

Thanks to all forum members who helped me with the decision, esp pcmx5 and Guran. You guys are spot on.

Big Big thanks to flycasta who supplied the diff and with service 2nd to none. Best diff man in Australia IMHO.

Which ratio did you settle on?

bootz · Postby **bootz** » Sun Feb 27, 2011 5:38 pm

4.1FR, and I can play with wheel tyre combos to my heart's content. :mrgreen:

Now to fit a big muther exhaust and CAI.

mitch_f1 · Postby **mitch_f1** » Thu Apr 14, 2011 8:49 pm

What an awesome thread.

So I have struggling to get my head around the difference in final gear ratios. So my NA6 supposedly has a 4.3 ratio diff (although it is a JDM import, so unsure about that...) If I went to a 4.1 or a 3.9 what kind of changes would I see? Would I be accelerating slightly faster and revving higher on the freeway. What is the optimum for a slightly modified NA6 5spd?

pcmx5 · Postby **pcmx5** » Thu Apr 14, 2011 9:01 pm

.Just the opposite. if you went from a 4.3 (ie. turns of the engine to turns of the diff.) to 4.1 you would be travelling faster for the same revs.Unless you find 20 RWKW from somewhere I would stay with the 4.3 with a 1.6.It was a really good set up , don't stuff it up.

Peter.

MX5-SP · Postby **MX5-SP** » Mon Jun 20, 2011 6:47 pm

Great Thread.

Does anyone have any ideas of the sort of effect to expect if I changed the SP to a 5-speed gearbox using the 3.9 torsen LSD? I find that 1st is basically a waste of time with all the grunt I get from the turbo. What would be the best combination gearbox/diff ratio?

timk · Postby **timk** » Mon Jun 20, 2011 11:42 pm

If you want to go taller you could get a 3.6 diff, which is what the SP came standard with. The NB8A came with a 5 speed and 4.1 diff so you swapping to a 5 speed in your car would be slightly taller than that.

Nuddy · Postby **Nuddy** » Fri Mar 24, 2017 10:54 am

Reviving an old thread.
I have not read through it all, last post was in June 2011

I have a 1998 NB8A, completely stock AFAIK until yesterday when I had the final drive (diff) swapped.
I am told the standard diff was an open diff with 4.1:1 ratio.
Before the swap I checked the speedo against GPS and found it to be 'spot on'.
After the swap I rechecked and found the speedo is now 8% 'optimistic'.
I was told the second hand unit from japan is a Torsen Type 2 with 4.3:1 ratio and it has NB8C painted on the housing.

Another check I did (on a private road) was max speed in 3rd gear (5 speed box).
The rev limiter limits to 7200 rpm (according to the stock tacho) and at that speed the gps was reading 130.00 km/h.
This is very useful for me if I compete in Targa Tasmania in the GT Sports Trophy class.
In that class the competitors are penalised if they exceed 130 km/h. The speed is monitored by the rallysafe unit.

My MX-5 is primarily for motorsport, tarmac rallying and maybe MX-5 Cup

In order to qualify for entry to MX-5 Cup I need to run lap times at Wakefield Park below 1:16

I imagine that changing from the open 4.1:1 to the Torsen 4.3:1 will help there too.

rascal · Postby **rascal** » Fri Mar 24, 2017 11:06 am

Nuddy wrote:The rev limiter limits to 7200 rpm (according to the stock tacho) and at that speed the gps was reading 130.00 km/h.
This is very useful for me if I compete in Targa Tasmania in the GT Sports Trophy class.
In that class the competitors are penalised if they exceed 130 km/h. The speed is monitored by the rallysafe unit.

I doubt you would want use the rev limiter as a way to keep your speed under 130..
Some sections are quite long/fast, and staying in a lower gear running on the limiter for long periods isn't a great idea.

Nuddy · Postby **Nuddy** » Fri Mar 24, 2017 9:17 pm

rascal wrote:
Nuddy wrote:The rev limiter limits to 7200 rpm (according to the stock tacho) and at that speed the gps was reading 130.00 km/h.
This is very useful for me if I compete in Targa Tasmania in the GT Sports Trophy class.
In that class the competitors are penalised if they exceed 130 km/h. The speed is monitored by the rallysafe unit.

I doubt you would want use the rev limiter as a way to keep your speed under 130..
Some sections are quite long/fast, and staying in a lower gear running on the limiter for long periods isn't a great idea.

I wasn't suggesting that. I was concerned that I would inadvertently exceed 130 in 3rd gear. I don't normally hit the rev limiter but change on the redline or before. Now I will know to change to 4th and back off and watch the speedo - if it comes to that.
I have dríven several of the TT stages slowly in my Patrol and those that I drove looked like I would have trouble reaching 130 between corners in a stock ND8a.
Seems to me the MX-5 would be pretty much ideal for the GT Sports Trophy class in that the competition would forfeit their advantage by having to back off down the straights while the MX-5 is accelerating all the way.