NC 6 speed - 4.1 final drive

Technical Area Engine, Transmission, Exhaust etc
1
  1. My model of MX-5 is: NC 2.0 6 speed
  2. I’m based near: London
  3. I’m looking for technical help or recommendations on: converting the final drive on my 2.0 6 speed from the standard 3.7 to a 4.1 from a 1.8 car. Anyone done this and know what’s involved? Of course would want to retain my LSD. Saw online that it’s been done but struggled to find much info. Believe US spec cars might have have this combination as standard?

Thanks

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If you use the diff from a 2.0 5 speed manual car this will give you the 4.1:1 and it will be already a LSD, easy to pick up off ebay. they are heavy to swap if just using axle stands but can be done. much easier with a ramp. Also you can do it without messing with the alignment by just undoing the wheel end of the suspension and prying out the driveshafts with a pry bar. I did to my track car last winter been a good upgrade. (I realize i am not answering your question but this method would be easier)

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I wasn’t aware that the 2.0 5speed cars had the LSD and 4.1 from the factory, in that case I will just go down this route, sounds much easier. Thanks very much for the response.

Did you have any issues with cruise control if fitted? Read online that changing the FD can effect it, but not sure if that was referring to ND MX-5’s

Now the search begins, can’t find any on eBay but will keep checking over the next few months and hopefully track one down.

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Sorry can’t help with the Cruise Control question. hope you find one soon.

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5

Hi, your speedo won’t be affected as it uses a wheel speed sensor. Right rear if I remember correctly.

It may affect DSC though as you need to tell the ECU the gear ratios while mapping. I have an RX8 gearbox and a 4.1 LSD I’m going to be transplanting into my car next year and mapping myself so I’ll see what happens with the “wrong” ratios entered.

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6

I’ve picked up what I think is a 2.0 5speed diff, although I need to take the cover off to check that it is what it was sold as. Will try to fit it over Xmas and report back if I have any issues.

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Hi, you can just mark inside the output with a paint pen and spin the input with a similar mark. Just over 4 turns of the input will be needed to rotate the outputs once (4.1:1) or just under (3.727:1).

This is how I tested mine as bizzarely it came from a 6 speed… The guy knew it was a 4.1 but I got it for £160 :smiley: so not sure he understood it was modified.

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