Differential ratios

Technical Area Engine, Transmission, Exhaust etc
1
  1. My model of MX-5 is: 2008 NC 1.8
  2. I’m based near: Suffolk
  3. I’m looking for technical help or recommendations on:

It looks as though I will have to replace the differential on my car in the coming months. Preferred option would be to buy a refurbished item with some kind of warranty on it.

As far as I can determine, the current unit has a ratio of 4.1:1. I note that others are listed for sale as 3.9:1. With my very limited mechanical knowledge, can anyone enlighten me as to whether dropping in a 3.9:1 unit is a) possible b) problematic? I’m presuming there would be marginal performance differences?

Thanks in anticipation

2

The only diffs that are fitted to the NC are a 3.7 in the six speed and 4.1 in the 5 speed.

If you fitted a 3.7 in your 1.8 it would accelerate slower and have higher gearing (less revs per mph)

3

Thank you for posting. Am I correct to think from what you have said that it is possible to swap for the 3.7, but not necessarily desirable? I wonder how much improvement there would be in MPG on a long run?