Diff for 6 speed

  1. My model of MX-5 is: MK2.5 Arctic/SVT
  2. I’m based near: Honiton
  3. I’m looking for technical help or recommendations on: Best diff set up.

I first bought an SVT as a replacement for my 1st MX5, but unfortunately it had a lot of hidden rust so I stripped it and bought a good condition MK2.5 Arctic Edition.

I then set about creating what I call a SVT+ as it now has, I believe, every factory optional extra including A/C!

During this I swapped the 6 speed over and noticed the Speedo was way high so I swapped the speed sensor from the 5 speed which solved that and it’s pretty close to GPS measured speed.

I noticed the other day about 80mph I’m sat at about 4000 rpm and was wondering if the stock diff in the arctic (I’m told was an LSD) is a different ratio to the LSD that was in the SVT which was why the Speedo was so far out. (Unfortunately I can’t remember the RPM before I swapped the gearbox as I did it pretty soon after buying the car.

So my question is, what would be the best set up and any advantages/disadvantages if I should swap the SVT diff in or leave it with the original which was paired with a 5 speed? I also have some poly mounts I’d do at the same time.

Many thanks!

(PFA of my most recent trip around the Welsh back roads!)

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The 5 speed diff will be a 4.1. The six speed diff is a 3.636

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3.9:1 in a MK 2, 6 spd.

Not in an SVT (original post!)

Is this the case for all Mk2s?

funny enough i know the differences with the diffs, speed drives and gearboxs, i was not correcting , just adding to important info also with the 6 speed on the 2’s in general.

6 speed not very common on the Mk2, but they were a 3.909 if fitted with a 6 speed.

The SVT engine sport six speed (as per the OP) will be a 3.636

Thank you, so what does that mean? If I leave it as is, it’ll accelerate slightly faster?
But if i swapped the SVT diff in it’ll have slightly lower rpm at the same speed?
Did the arctics definitely come with an LSD, seems to lock up when I try and get it to slide but I’m not 100%

RS, VS, 10th, sport.

You’ve managed not to answer the post and dragged it off topic. :crazy_face:

OK i’l answer it , swap the diff , it will end up bust , it was not the best that was fitted to the MX 6 spd… 3.6 differential with a Super Fuji clutch style differential , the clutch plates within this diff fail over time and can end badly, we think it is down to being tested at MOT time on a rolling road and should really be teasted the same as a 4 x 4, ride it until it goes and swap it for a better one…

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I`m looking for a 3.9, I can fit 3.6 or 4.1 to exchange if this helps. Based near Chester.