Considering Upgrade to 3.55:1 Gear Ratio

Discussion in 'V6 3.7L Engine / Mods: Bolt-ons, Exhaust, Tuning' started by Zeenobit, Jul 5, 2015.

  1. Zeenobit

    Zeenobit Well-Known Member

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    Apologies for any ignorance, but this is a new area to me, so I need a bit of help.

    Originally, when I bought my V6, I didn't pick the 3.55 Gear Ratio option, so I have the 3.15 right now.

    Recently, I stumbled across this: http://www.americanmuscle.com/frpp-355-gears-2015.html

    So I have a few questions:

    1. How much of a practical difference is switching to the 3.55 compared to 3.15?
    2. How easy is the installation? Is it easy to undo the installation if needed (car is leased, with 80% chance of buyout at the end, but I want to be on the safe side).
    3. How badly does 3.55 affect fuel economy for a daily driver?
    4. For a daily driver, am I correct in not switching to 3.73 to keep things balanced? Especially during winter, I don't want to have a risk of losing traction every time I launch.
    5. I have an automatic transmission. Would this cause issues besides having to adjust the shift points?
    6. Does this mean my car would need a tune after installation? This article (http://www.americanmuscle.com/mustang-rear-differential-gears.html) says it may, especially for automatic.
    7. How can I guarantee the adjustments to the transmission are safe, and what do I need to watch out for from the installer?

    Thanks in advance!
     
  2. bluebeastsrt

    bluebeastsrt Oh boy

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    The 3.7 doesn't make a ton of torque. I know. I have one. So I'd go with a 3.73 gear set if I were going to the expense of changing gears. It's not an easy back yard job and unless you have pretty good mechanical skills. I'd leave this job to the pros. typical install is $400-600 labor plus price of parts. It wont hurt your transmission at all but a tune would not only ad more power but it'll change your shift points. Also it'll reset your spedo for the new gears.
     
  3. DR_

    DR_ Well-Known Member

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    I don't think any of the other shorter final drives fit into the 3.15 carrier so you would have to swap a complete pumpkin.
     
  4. OP
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    Zeenobit

    Zeenobit Well-Known Member

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    Not planning on installing it myself. But I want to know if it's an easy install and whether or not it is reversible back to stock. Do the professional installers normally include the speedometer and shift point adjustment in the installation, or is that normally a separate thing? It'd be pretty useless to install and totally break the speedometer and shift points.

    Also, don't you think the 3.73 would be too much torque for a daily driver (especially in winter)?

    Not sure what you mean by "shorter final drives" and what constitutes a complete pumpkin. Could you explain more, please? :p
     
  5. Five Oh Brian

    Five Oh Brian Mustang Guru

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    8.8 ratios all use the same carrier. 8.8's can easily accept all Ford ratios from 2.73's all the way up to 5.14's. 4.56's and steeper requiring a different crosspin or notching a pair of ring gear teeth, but all other ratios fit without any trouble.


    Sent from SYNC in my '14 Mustang GT...
     
  6. bluebeastsrt

    bluebeastsrt Oh boy

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    It is easily reversed for another $400-600 dollars but once you get them in and feel the added acceleration you'll put the stock gears on ebay. If the gears are installed correctly there is no chance of damaging the transmission or the rear. No 3.73 will not be two much even in winter. You'll just have to go a little easier on the throttle.
     
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  7. DR_

    DR_ Well-Known Member

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    I see. Doing a little more research and it appears the differential, not the carrier, is what needs to be replaced if going with the 3.55 from the 3.15. That still adds a lot of extra cost to the swap.
     
  8. DR_

    DR_ Well-Known Member

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    shorter final drive = numerically higher gears
    so going from a 3.15 to 3.55 is going to a shorter final drive.

    The pumpkin is the entire carrier, differential, final drive.
    Basically the big round thing you see back there, hence pumpkin :cheers:
     
  9. OP
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    Zeenobit

    Zeenobit Well-Known Member

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    Makes a lot more sense now. Thanks. lol

    So I will need to change the differential if I want to upgrade to the 3.55 as well?
     
  10. re-rx7

    re-rx7 Ruck the night away

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    Having 3:73 doesn't make you necessarily faster. Remember, that you will shift more and that's time.
     
  11. BmacIL

    BmacIL Enginerd

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    You do not need to change the differential to go to 3.55 or 3.73 gears. You cannot use the Torsen diff with the 3.15, but you can put any of the other gears on the clutch pack diff (everything that's not a GT PP has that).

    If fuel economy is a concern to you I wouldn't do the swap. If you can accept the 2-3 mpg hit on the highway, then it's your call. The auto has shorter internal gearing than the manual and the 3.55 felt just right in the V6 w/ manual.
     
  12. OP
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    Zeenobit

    Zeenobit Well-Known Member

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    Thanks for the info. Fuel economy isn't a big deal to me. I think 3.55 is a nice balance too. Have you driven the 3.15 by any chance?
     
  13. thehunterooo

    thehunterooo Well-Known Member

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    The swap is worth I think. If you look at reviews of the last gen 3.7, they normally
    came with the 2.73 gears (the PP had 3.31) the difference in 0-60 was almost a half second I think on some of the tests. I had the V6 PP myself thankfully :D

    The 3.55 gears is a good spot to be. I think the speedo will be off though, never looked into swaps myself.
     
  14. BmacIL

    BmacIL Enginerd

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    I actually drove the V6 in 3.15 and 3.55 for both auto and manual. 3.55 auto was very nice!
     
  15. OP
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    Zeenobit

    Zeenobit Well-Known Member

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    So you'd say the difference is quite noticeable? I haven't driven the two myself.

    My only concern now is the fuckery with the speedometer and shift points for the automatic transmission. How do they usually fix this to ensure the results are as precise as stock? Or can it even be as precise as stock?
     
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