3.55 differential swap in an automatic... Anyone done it?

[GT500Steve]

New to the S-550s, I was curious if any of you guys have done the upgrade to the 3.55 iron housing that Ford Racing offers. More importantly, I was curious what effect it had on ETs. I've heard from severalpeople that the cars run slower with gears, but after taking mine to the track (completely stock) I personally think it could benefit from the 3.55's. Any input appreciated.... Thanks!

 

[scotmach]

There's a quarter mile list going on another forum and the guys with 3.15's are all at the top. But the times between the 3.15 guys and the guys with 3.55's are negligible. My point being you will gain nothing plus it will be expensive after the new housing, gears, and Whipple flare tool which is required.

 

[Saleen_1977]

Im about to put on 4.09 gears, Ill let you now how hard it pulls. With comp cams and new springs to push up redline, it should be sweet.

 

[django]

There's a quarter mile list going on another forum and the guys with 3.15's are all at the top. But the times between the 3.15 guys and the guys with 3.55's are negligible. My point being you will gain nothing plus it will be expensive after the new housing, gears, and Whipple flare tool which is required.

Where can i find this list?

 

[burnin4]

New to the S-550s, I was curious if any of you guys have done the upgrade to the 3.55 iron housing that Ford Racing offers. More importantly, I was curious what effect it had on ETs. I've heard from severalpeople that the cars run slower with gears, but after taking mine to the track (completely stock) I personally think it could benefit from the 3.55's. Any input appreciated.... Thanks!

It's going to depend on your setup and goals. Probably best to plug your info into the gearing calculator I listed below. For me, 3.15's are best because my car traps 133-134 and my 3.15's don't go into 4th till 140mph, so I only have to shift twice. If I had 3.55's I'd be going into 4th at 124 and the extra shift would probably cost me some et. I have no doubt that 3.55's would be more spirited around town and quicker through the 8th, but swapping rear diff's is cumbersome with the new 8.8+, 3.15 cars come with aluminum housings, no upgradable diff's or gears available. You gotta buy the pp cast diff casing, then the diff, then the r&p, as well as a Whipple flare tool to change your calibration.

http://www.apexgarage.com/tech/gear_ratios.shtml

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

 

[burnin4]

Where can i find this list?

Mustang6g, Dragstrip section.

 

[GT500Steve]

It's going to depend on your setup and goals. Probably best to plug your info into the gearing calculator I listed below. For me, 3.15's are best because my car traps 133-134 and my 3.15's don't go into 4th till 140mph, so I only have to shift twice. If I had 3.55's I'd be going into 4th at 124 and the extra shift would probably cost me some et. I have no doubt that 3.55's would be more spirited around town and quicker through the 8th, but swapping rear diff's is cumbersome with the new 8.8+, 3.15 cars come with aluminum housings, no upgradable diff's or gears available. You gotta buy the pp cast diff casing, then the diff, then the r&p, as well as a Whipple flare tool to change your calibration.

http://www.apexgarage.com/tech/gear_ratios.shtml

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

Thanks for the info.... Two very useful links.

My goals for the car "short term" are probably a 150 shot and 20" drag radials. Looks like with the tire diameter and the estimated mph I "think" it would run the 3.15s are the better choice.

Long term it will have a TVS, and I am sure the 3.15s will be better suited for the torque the blower makes off idle.

 

[H-TownMachI]

Does anyone have the optional 3.55's for the automatic? Is that an aluminum housing also?

 

[bunk22]

I have the optional 3.55's on my auto, the premium package. No idea if an aluminum housing though.

 

[5.0jake]

There's a quarter mile list going on another forum and the guys with 3.15's are all at the top. But the times between the 3.15 guys and the guys with 3.55's are negligible. My point being you will gain nothing plus it will be expensive after the new housing, gears, and Whipple flare tool which is required.

Actually the auto with 3.55's appear to be the fastest bone stock according to the following:

http://www.mustang6g.com/forums/showthread.php?t=16739

 

[scotmach]

Actually the auto with 3.55's appear to be the fastest bone stock according to the following:

http://www.mustang6g.com/forums/showthread.php?t=16739

Like I said, the times are negligible between the two and not worth the swap. Plus if one is going to do the swap it's safe to assume they won't be keeping their car stock. That's when the 3.15's really shine over the 3.55's for the simple fact you can avoid the shift into 4th gear.

 

[5.0jake]

Like I said, the times are negligible between the two and not worth the swap. Plus if one is going to do the swap it's safe to assume they won't be keeping their car stock. That's when the 3.15's really shine over the 3.55's for the simple fact you can avoid the shift into 4th gear.

While I agree the results will be negligible, especially if modded, you also said 3.15's are all at the top which isn't true according to my link regarding the stock configuration..

You also have people like me who are forever leaving their car bone stock and enjoy the extra punchy feel the auto 3.55 delivers vs the 3.15's.

To the OP, prob not worth the swap if numbers are primarily your concern. A gear swap can be like opening a can of worms.

 

[Red Turtle]

While 1/4 numbers are considered, that is only 1% of the time for me. I would love to have the 3.55's for daily, as my rear wheel/tire combo is 28.5" making the gears very long with the 3.15's.