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Hi everyone,

Just wondering if anyone had put in a 4.1 torsen in the SP? Was there any significant difference in low end torque compared to the 3.636 open diff? I read that it makes the first gear very short and if so will it affect the drivability of the car on normal road? The car will be setup for mostly normal road driving and the occasional track day. Thanks everyone.

Without having done that exact swap I can say yes, it will be a decent difference. I went from 4.1 to 4.3 in my 5 speed NB and it was noticeable, jumping from 3.6 to 4.1 is going to be a bigger difference again. There are a few people around with 4.3 diffs matched with 6 speed boxes too, and although it's buzzy at highway speeds, it doesn't otherwise affect drivability. Depends how much cruising at high speed you do. If a 4.3 with 6 speed is ok, a 4.1 will be fine.

The Torsen will be an improvement over the open diff.

4.1 with a 6-speed is very acceptable to me, but YMMV (and I don't have an SP).

There was a thread here just recently at which the differences were discussed at some length, a bit of searching should turn that up.

With the desire for primarily road driving and the extra power/torque of the SP you really don't need to go for a 4.1 diff, unless you really enjoy changing gears around town.....

My SE has fairly modest mods (puts it around the same power level as an SP ex-factory) and I wouldn't want shorter gearing.

The best option for you would be to try and find a complete SE diff + housing + driveshafts (these are unique for the SE diff) and do a transplant.
You keep the current ratio but get a Torsen 2 centre and slightly stronger driveshafts to boot (it's debatable whether these are really required though).

Lower diff ratios are helpful for naturally aspirated MX5's but unless you're really doing serious trackwork not really necessary for forced induction IMHO.

On my SP ( stock standard ) the current setup that i'm running is a 3.9 torsen diff, lightened flywheel and 215/45/16 PS3 tyres on a 7 inch rim.

So far these mods have given me peppy acceleration with plenty of lateral grip with enough sidewall flex for a comfy ride when I'm out driving on country roads.

4.1 will mean plenty of gear changes at lower speeds, i don't recommend it.

Tezzax5 wrote:On my SP ( stock standard ) the current setup that i'm running is a 3.9 torsen diff, lightened flywheel and 215/45/16 PS3 tyres on a 7 inch rim.

So far these mods have given me peppy acceleration with plenty of lateral grip with enough sidewall flex for a comfy ride when I'm out driving on country roads.

4.1 will mean plenty of gear changes at lower speeds, i don't recommend it.

What he said. I had a SP with a stock 3.6, and the difference between an open and LSD with stock ratio in the SP is chalk and cheese. Lower gear ratios for a street dríven SP are not recommended.

Non turbo NBs benefit much more from a lower final drive than turbo NBs do.

Thanks everyone, I will wait for 3.9 torsen. I read that it is only available in the 10E and they are hard to come by.

They were available overseas so talk to an importer like MX5 Mania, MX5 Parts or MX5 Plus. They may have either some in stock or be able to source one.

I've got 160rwkw and 3.9 with 6 speed. A stock SP is about 130rwkw. Definitely wouldn't go any higher than 3.9 or 1st will be way too short and you'll be changing gears too much.

Thanks guys. I will check with MX5 mania, MX5 parts, MX5 plus as well as the ebay link to see if they have it and how much it cost to get them over to Perth. Hopefully it wont cost a bomb. Otherwise it could be a good opportunity to have a short holiday over in the eastern states and bring the diff back haha.

coldfire wrote:...I will wait for 3.9 torsen. I read that it is only available in the 10E...

ADM 10AE was 3.6 - see following for the actual Mazda Aust spec sheets where this is detailed:
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