Changing diff ratios

[abstruse1]

Ford offers the GT with 3.55:1 and something around 3.85:1. Can I replace my 3:55 with the 3.85 without having to tune? Big question since no one offers tunes for the 2025s.

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[86pagt]

3.73 is the other ratio that comes in the manual performance pack GT. I’m not much help on the tune part, if you have a manual you might get away with it. if you have a 10 speed I would think you would need to do something … 1st gear would be pretty much useless.. which maybe the reason ford did the 3.55s in the 10 speed performance pack cars.

 

[robvas]

Steeda has 4.09's in their 2024

Never heard of 3.85, 3.73 maybe?

 

[roket]

the closest you will find to 3.85 is 3.73. if i remember right, you need to tell the BCM with Forscan about the different ratio and it should be all good from there. but it wouldnt hurt to double check for certain

edit: ignore that last part. i've been informed it's more than just a BCM thing

 

[abstruse1]

Yes, 3.73 is what I meant.

 

[Trap]

I would go with the 4.09's if you are going to do that. The 3.73's are geared a little lower but not enough, it would still be geared pretty high with the manual Transmission.

 

[abstruse1]

I have the auto tranny

 

[abstruse1]

Unfortunately, it appears that no one has tuning software for the 25s yet.

 

[EgoBoost]

Unfortunately, it appears that no one has tuning software for the 25s yet.

If you haven’t yet heard, tuning is available. I’m trying to change the 3.55 in my manual to at least 4.09. I’m going to reach out to Steeda to see how I can go about it. Good luck.

 

[Junkyard Dog]

https://www.mustang7g.com/forums/th...n-a-s650-that-has-no-access-to-tuning.160889/

Steeda chimed in

Yes - sorry, I did get a response from our team.​

​

Manual transmission cars may act differently, we do not know yet ... we only did our Automatic.​

​

We have ranged from 3.31, 3.55, 3.73 and 4.09 gears in our car. The only issue we have seen is the speedometer difference between the various ratios.​

​

Hope that helps!​

​

Best Regards,​

​

TJ​

​

And another poster chimed in that his speedometer reads correctly after changing gears.

I know this is an older thread, but I just put a set of 3.73’s in my 10r80 car. I have had no issues whatsoever. I haven’t changed anything in computer yet and speedometer is still correct according to gps. I went from 3.15’s to 3.73’s.​

 

[JPGC_S650]

In a manual car, going from 3.55s to 4.09s or 4.30s would be my choice. The cost/effort to go to 3.73s from 3.55s wouldn't be worth it, IMHO....unless you are trying to maximize shifting on certain tracks/ drag strips.

 

[Junkyard Dog]

OP has an automatic.

 

[drive_55_not]

https://www.mustang7g.com/forums/th...n-a-s650-that-has-no-access-to-tuning.160889/

Steeda chimed in

Yes - sorry, I did get a response from our team.​

​

Manual transmission cars may act differently, we do not know yet ... we only did our Automatic.​

​

We have ranged from 3.31, 3.55, 3.73 and 4.09 gears in our car. The only issue we have seen is the speedometer difference between the various ratios.​

​

Hope that helps!​

​

Best Regards,​

​

TJ​

​

And another poster chimed in that his speedometer reads correctly after changing gears.

I know this is an older thread, but I just put a set of 3.73’s in my 10r80 car. I have had no issues whatsoever. I haven’t changed anything in computer yet and speedometer is still correct according to gps. I went from 3.15’s to 3.73’s.​

I don't see how the speedo was correct unless they went with a taller tire,

The HP Tuner MPVi2 will change the gear and tire ratio's.

Using VCM Scanner and select the Green Special Functions button [ looks like a Power Button ] and select Speedometer.

Change the gear and tire revolutions and save.

It worked, I changed from 3.15'w to 3.73's and the speedometer was 7mph off on a test drive.



.

 

[MNPony]

I swapped my 3.15 diff for the Ford Performance 3.55 diff. It took a lot of investigating by my dealer but they eventually figured out how to recalibrate for the new gear ratio. They used a Ford Performance Procal 4 tuner. In the menu on the tuner there's a section for changing the gear ratio and/or the tire diameter (it's actually revolutions per mile). They simply replaced 3.15 for the gear ratio with 3.55. Speedo was instantly accurate and the automatic tranny shifts perfectly.

 

[Junkyard Dog]

I swapped my 3.15 diff for the Ford Performance 3.55 diff. It took a lot of investigating by my dealer but they eventually figured out how to recalibrate for the new gear ratio. They used a Ford Performance Procal 4 tuner. In the menu on the tuner there's a section for changing the gear ratio and/or the tire diameter (it's actually revolutions per mile). They simply replaced 3.15 for the gear ratio with 3.55. Speedo was instantly accurate and the automatic tranny shifts perfectly.

Very useful information with actual experience. Thanks. This is helpful to several here, I am sure.

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