Please post if you have changed the rear axle ratio of a manual transmission Mustang GT 2018-20

[GreenS550]

As calculated, the 2018 and up manual trans Mustang GT PP (3.73) has long gearing. To equal the same gearing as the '15-17, the '18 and up would need a 4.21:1 rear axle ratio. Who has changed their axle ratios and what was your experience?

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[I Bleed Ford Blue]

It might be easier to find a close ratio MT-82 out of a wrecked 15-17 and swap it than to change out rear gears. And if you want you can get the calimer stage 3 upgrade done and it will be a lot stronger. Calimer does not upgrade the D4 versions of the MT-82's (used in 18+) only the 11-17 models.

 

[GEBRONI]

You can change your rear tire set up to also change the effective gearing instead... Example 3.73 PP mustang with 275/40r19 wheel provide effective 3.65 gearing. I have 3.55 on manual, so if I change my wheels to 285/35r19 I will have an effective 3.6 gearing. If I run 285/30r19 I will get effective 3.73 gearing.

 

[GreenS550]

Question still stands. Who has changed the rear axle ratio? What gear did you put in? Results?

 

[Mikepol2]

Ford Performance 4.09's...no regrets.

https://www.mustang6g.com/forums/threads/how-are-people-liking-4-09-gears-in-the-mt82.111146/

 

[GreenS550]

Ford Performance 4.09's...no regrets.

I'm curious. Did you feel more torque down low taking off in 1st? Would you have done more, i.e. lower ratios; 4.2+ etc?

 

[Mikepol2]

For sure. I can start in 2nd now almost as easy as 1st if the road is flat. Mid-range pulls in 3rd are pleasantly snappier too. Was considering 4.30's originally but now having had the 4.09's with the 2018+ manual gear ratios, I'd never go to 4.30's even if it was free.

 

[GreenS550]

Thanks! A lot of us old muscle car guys that put 4.10s, 4.30s, 4.56 gears in remember that great quick fun takeoffs. Unfortunately I've gone FI, but if I had stayed NA, I would do it for sure.

 

[Wittbrij]

2018 gt, I went from from 3.55 to 4.09 with 305/35r20. I made a chart and the rpm/mph are nearly identical to the 15-17 with 3.73 with pp wheel and tire set up. Black line / teal in the graph

 

[GreenS550]

Thanks! That's 6th gear, correct? Because looking at 1st you would have needed 4.21:1 to equal 3.73 in the '15-17. So, maybe the 4.09 is the best of both worlds. Like the old 373 in 6th yet not so low in 1st.
I would have done this before the Whipple if I had it to do over...

 

[Wittbrij]

Thanks! That's 6th gear, correct? Because looking at 1st you would have needed 4.21:1 to equal 3.73 in the '15-17. So, maybe the 4.09 is the best of both worlds. Like the old 373 in 6th yet not so low in 1st.
I would have done this before the Whipple if I had it to do over...

The green, with numbers associated were 3.55 and 305/35r20 tires I filmed driving speeds and ran torque pro to get data points. However I hadn't adjusted forscan for tire size yet. I'd assume the altered trendline is due to wind resistance.

The green line, 6th actual and pink line, 5th actual the 4.09s hit right in between. I wouldn't go higher than 4.09. I was looking for a 3.9x but struck out

On some other forums I calculated wheel torque, you'd need to get to 484 crank hp with 3.55 to "out torque" 4.09 at stock power levels.

 

[Mrzero]

I was doing some gearing calculations on Tremec's site and this is what i got based on the stock PP2 tire size 305/30/19 (26.2") with 4.09 gears. This rearend and tire combo will get you really close to 15-17 gearing.

 

[LucB]

I am seriously considering this as well for my 18 PP1. My only hangup is I’m worried it’s not enough of a change. If they made 4.20’sish I would have already bought them.

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