Anyone running a 4.09 rear gear ratio ?

Discussion in 'United Kingdom' started by Alfa Male, Apr 24, 2020.

  1. Alfa Male

    Alfa Male Well-Known Member

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    The gear ratios in the 2018+ M6 feel taller than the previous version I had, so I was looking at the 4.09 rear gears to improve acceleration and low down torque

    https://performanceparts.ford.com/part/M-4209-88409A

    So has anyone (in the UK) had this fitted ? I’d welcome your real world thoughts and any indication on where to get the work done / costs etc would be grateful received.
     
  2. WD Pro

    WD Pro Well-Known Member

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  3. maddog1982

    maddog1982 Well-Known Member

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    Are they different? I think the uk 2015s were 3.55 ? I can just about hit 60 in 2nd. I guess you can do more?
     
  4. cib24

    cib24 Well-Known Member

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    The 2019+ manuals have revised gear ratios making them slower than the 2015-17 cars up to about 80 mph when the 2019s shift into 3rd. The automatic is about 1 second faster in th 1/4 mile which is a lot!

    I have 4.09 gears and a Torsen diff (standard on the USA Performance Pack cars, GT350 and GT500) but I have not had them installed yet as we entered lockdown.

    The 4.09s will make a huge seat of the pants difference and I'd guess it would feel like you gained 60 hp and torque in 1st through the top of 3rd.

    See the difference in max mph in each gear across the different specs:

    upload_2020-3-1_23-28-36-png.png
     
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  5. Supersolo

    Supersolo Well-Known Member

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    I believe the diff ratio hasn't changed between the 15-17s and the 18 onward. However, the GB ratios have.
    I get just over 50 in 1st and reach 70 long before red line, in 2nd.
     
  6. maddog1982

    maddog1982 Well-Known Member

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    Fantasic information!!!

    Sorry all, I read it and assumed we were talking about the Diff - DOH. So what kind of costs would AlfaMale be looking at to have this done out of interest? I imagine its quite a bog job? My tach guage shows the red at 6500 but I assume the rev limiter cuts at 7200 I have never been near it hence thinking 2nd tops out around 60.
     
  7. cib24

    cib24 Well-Known Member

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    Redline on a 2015-18 Mustang is 7000 RPM whereas on the 2019+ Mustang it is 7400 RPM.

    I'm showing 7200 RPM in my table as that is where the highest shift point is in the settings and where I usually shift to avoid banging the limiter.

    The 2015-18s cant revn out to 7400 RPM and higher without any issues but only with an ECU remap.
     
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  8. OP
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    Alfa Male

    Alfa Male Well-Known Member

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    wow that’s really interesting so the gear ratio with the 4.09 brings it back to the same as the 15-17 model in terms of speed vs rpm

    I’m watching this with interest, love to hear your feedback and know the costs involved as I’m seriously considering this.
     
  9. WD Pro

    WD Pro Well-Known Member

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    I think there’s a few watching with interest - we need a group buy ... lol

    Feedback from the guys in the states that have done it is good, and they start from a better position than us :like:

    WD :like:
     
  10. OP
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    Alfa Male

    Alfa Male Well-Known Member

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    I might give Modurstang a call when this lockdown ends to get a price and opinion !
     
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  11. cib24

    cib24 Well-Known Member

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    It's not just about improving in gear acceleration with the 4.09, but actually being able to enjoy using 1st through 4th gear in most situations. One thing I really hate about the 2019 Mustang is on a normal road when you want to hustle the car you basically never get out of 2nd gear because it goes to 80mph....And then you get onto an A road and 3rd goes to 120mph so you can't really use more than 2 seconds of 3rd before you're being really irresponsible in public.
     
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  12. Steeda UK

    Steeda UK Well-Known Member
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    Don't forget you will need a remap as well if you change the gears to make sure the speed works properly....

    We can supply the official Ford Racing gear packs and install kits if required... (plus remaps as well of course)
     
  13. WD Pro

    WD Pro Well-Known Member

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    Go on then, spill the beans ... :like:

    How much would supply / fit / make the minimum adjustments (i.e. not a full remap / keep the insurance company happy / just correct the speed readings etc) job cost ?

    Whist your in there, what would the additional be to swap to a ATB ?

    Cheers,

    WD :like:
     
  14. Steeda UK

    Steeda UK Well-Known Member
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    Well the 4.09 kit would be £598 inc vat (kit & install kit)

    The wavretac diff is here: https://www.steeda.co.uk/collection...rac-s550-mustang-atb-lsd-diff-for-ecoboost-gt

    Thats £1369 inc vat I believe....

    Install would need to be costed by the people you choose to do it and also account for new synth oil etc...

    As for remap , you may as well go for the full Steeda "Tunes for life" package to get it done right speedowise and engine tuning wise.... 8)
    Then your updates when you do want more power etc are free....

    https://www.steeda.co.uk/collections/mustang-s550-gt/products/sct-x4-tuner-steeda-tunes
     
  15. OP
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    Alfa Male

    Alfa Male Well-Known Member

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    Interesting ! Is the Wavretac Diff required or is that an optional part ?
     
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