Gear ratio issue

[GreenS550]

I have been thinking of how to get more grunt off the line in my Bullitt. These gears coupled with the higher RPM of peak HP has me looking at options. Yes, I could put a 2017 MT82 in my Bullitt. Too expensive and other issues. May as well put a blower in for a few bucks more.

So, I compared gear ratios of our Bullitts with pre-2018 Mustang GTs. Here are links to the two specs:

https://media.ford.com/content/dam/fordmedia/North America/US/2015_Specs/2015_Mustang_Specs.pdf

https://media.ford.com/content/dam/...ses/Mustang/2018Ford_Mustang_Tech_Spec_EU.pdf

Ford does state the ratios are to meet mileage standards. Apparently just a bit of shifting with our more powerful cars could drop MPG 1 and make our Mustangs "gas guzzlers".

So, doing a bit of math, for 1st to be the same final drive ratio as a 2017 GT with 3.73s our Bullitts would need a 4.21:1 axle ratio. That ratio, if it were available would still leave 2nd a bit longer than the 2017 transmission. These are really long gears.

Now that said I'm thinking 4.11:1 albeit a bit longer than the 2017s might be just perfect. With our ridiculous 6th gear, highway cruising would still give decent 22-23 MPG.

Any thoughts?
`

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[Bullitt0819]

Sounds appealing; I rarely hit 6th at it is. Is the new IRS as easy to swap as the old 9 inch? Would you have to buy a 'tune' in order to change the speedo readout?

 

[GreenS550]

You would need a tuner or some device. Since I have the Steeda tune and an SCT 4 tuner oh, it would be simple. The nine inch differentials of long ago or a pig style or third member. Our IRS differentials will just require having the gears replaced and set with proper backlash and thrust washers. I'm thinking probably $300 in labor and $300 for the gears. Something like that. I'm wondering if done at a Ford dealer if it would still be warranted. I don't know the answer to that.

 

[Bullitt0819]

... Our IRS differentials will just require having the gears replaced and set with proper backlash and thrust washers. I'm thinking probably $300 in labor and $300 for the gears. Something like that. I'm wondering if done at a Ford dealer if it would still be warranted. I don't know the answer to that.

Can the swap be done in situ, or do you have to pull the diff?

 

[Schwerin]

I find it funny how many complain about the long gearing but most the gears are +0.10 more than the 3650 in the 01-04 3650 tranny and that made a lot less TQ.

Just do like we did 15yrs ago. Put in a 4.09 or a 4.30, 4.56 if you drag, and call it a day.

 

[aileron]

I find it funny how many complain about the long gearing but most the gears are +0.10 more than the 3650 in the 01-04 3650 tranny and that made a lot less TQ.

Just do like we did 15 50 yrs ago. Put in a 4.09 or a 4.30, 4.56 if you drag, and call it a day.

Fixed it for you

 

[Schwerin]

Fixed it for you

I'd just glad I'm on a platform that shares less parts with the 70's than my last mustang. lol

 

[Racerx009]

I have been thinking of how to get more grunt off the line in my Bullitt. These gears coupled with the higher RPM of peak HP has me looking at options. Yes, I could put a 2017 MT82 in my Bullitt. Too expensive and other issues. May as well put a blower in for a few bucks more.

So, I compared gear ratios of our Bullitts with pre-2018 Mustang GTs. Here are links to the two specs:

https://media.ford.com/content/dam/fordmedia/North America/US/2015_Specs/2015_Mustang_Specs.pdf

https://media.ford.com/content/dam/...ses/Mustang/2018Ford_Mustang_Tech_Spec_EU.pdf

Ford does state the ratios are to meet mileage standards. Apparently just a bit of shifting with our more powerful cars could drop MPG 1 and make our Mustangs "gas guzzlers".

So, doing a bit of math, for 1st to be the same final drive ratio as a 2017 GT with 3.73s our Bullitts would need a 4.21:1 axle ratio. That ratio, if it were available would still leave 2nd a bit longer than the 2017 transmission. These are really long gears.

Now that said I'm thinking 4.11:1 albeit a bit longer than the 2017s might be just perfect. With our ridiculous 6th gear, highway cruising would still give decent 22-23 MPG.

Any thoughts?
`

I installed 4.09 gears in my 2019 Bullitt pulls hard and no highway issues. I think 4.11 would be even better

 

[OvalBlue26]

I installed 4.09 gears in my 2019 Bullitt pulls hard and no highway issues. I think 4.11 would be even better

Racerx009, Did you have any issues with throwing codes or speedometer calibration after the 4.09 R&P install? I ordered the 4.09 and am trying to anticipate any issues. Thanks.

 

[Schwerin]

Racerx009, Did you have any issues with throwing codes or speedometer calibration after the 4.09 R&P install? I ordered the 4.09 and am trying to anticipate any issues. Thanks.

Everything I've seen says that manual cars don't need to be calibrated, only Auto's

 

[OvalBlue26]

Everything I've seen says that manual cars don't need to be calibrated, only Auto's

I reached out to Ford Performance and got this reply:
Yes, you will have to find a calibration to adjust for the 4.09 gear. If not you will have issues.
Ford Performance does not have one for the Bullit.
Matt Korczyk
Ford Performance Parts Vehicle Coordinator
Ford Performance Parts Tech LIne
(800) 367-3788

 

[ice445]

Everything I've seen says that manual cars don't need to be calibrated, only Auto's

2019 and newer will need tuning for any ratio over 3.77. This is because of the auto rev match mostly because the computer doesn't have tables for anything over that 3.77 mark.

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