Swapping Diff ratio from 3.55 to 3.15 can it be done

666mac · Mar 16, 2018

Guys we in the UK have PP cars with 3.55 rear end I'm looking to fit 3.15 gears and torsen as we dont get them in our pp cars any idea if the 3.15 gears will fit any help be great.
Reason is I run 325 30 19 with 800bhp and I'm shifting gears constantly.

UAmach1 · Mar 16, 2018

I don't see any reason it can't be. I assume UK has the same rear as the US.

ScottyRyan2018 · Mar 16, 2018

666mac said:
Guys we in the UK have PP cars with 3.55 rear end I'm looking to fit 3.15 gears and torsen as we dont get them in our pp cars any idea if the 3.15 gears will fit any help be great.
Reason is I run 325 30 19 with 800bhp and I'm shifting gears constantly.

Can you add the TORSEN T-2R differential to the 3.15 gear? I know you can to the Ford 3.31, 3.55, 3.73 and 4.09.

ctandc72 · Mar 16, 2018

The differential itself is different. In other words when going from OEM 3.15 gears to anything lower (higher numerically) you have to get a compatible differential - like this one:

https://www.cjponyparts.com/ford-pe...raction-lok-34-spline-8-8-2015-2017/p/M4204M/

I'm not sure if you can swap 3.15's into an OEM 3.55 differential.

I have a complete 3.15 limited slip iron case differential sitting in my garage that came out of my '17 when it had @ 2K miles on it. Shipping would likely be pricey though.

EFI · Mar 16, 2018

The differential is a separate unit from the ring and pinion. As long as it's made for the Ford super 8.8 (2015+) I don't see why you can't put any ring & pinion combination you want.

ctandc72 · Mar 16, 2018

EFI said:
The differential is a separate unit from the ring and pinion. As long as it's made for the Ford super 8.8 (2015+) I don't see why you can't put any ring & pinion combination you want.

I'm aware it's a separate unit. What I am saying if you have a factory 3.15 geared car, you cannot use your factory diff with lower gears (3.31, 3.55, 3.73 etc) they won't work.

I simply don't know for sure if you can go the other way. In other words, will 3.15 gears fit in an OEM differential that had 3.73 from the factory.

TexasRebel · Mar 16, 2018

EFI said:
The differential is a separate unit from the ring and pinion. As long as it's made for the Ford super 8.8 (2015+) I don't see why you can't put any ring & pinion combination you want.

The 3.15 is not a Super 8.8

Gibbo205 · Mar 16, 2018

Just to point out UK PP cars have a 3.55 traction LOK as standard.

Mac wants to swap out his traction LOK for Torsen LSD, which should be a simple swap out.

But he also wishes to throw the lowest ring and pinion in he can, which from research he has done looks to be a 3.31 in the super 8.8 ?

666mac · Mar 16, 2018

Thanks for the comments guys ;-) as I have discovered looks like 3.31 and Torsen is the way forward with some 305 35 20 tyres this should push top speed up to 200mph and give beter drivability. :-)

c-rizzle · Mar 16, 2018

666mac said:
Thanks for the comments guys ;-) as I have discovered looks like 3.31 and Torsen is the way forward with some 305 35 20 tyres this should push top speed up to 200mph and give beter drivability. :-)

Are you adding a supercharger and other mods. I don't think you can hit 200 mph with bolt ons. And obviously you need to removed the electronic limiter with a tune.

666mac · Mar 16, 2018

5

c-rizzle said:
Are you adding a supercharger and other mods. I don't think you can hit 200 mph with bolt ons. And obviously you need to removed the electronic limiter with a tune.

Hay pal car has whipple, kooks rhd headers race cats etc etc 800 bhp we hit the limiter at 173.88 mph just over half mile running 325 30 19 tyres. Lund has already said the car limiter can not be removed pisser so fitted an ABS kill switch now just need to make the gears taller.

revtime · Mar 17, 2018

TexasRebel said:
The 3.15 is not a Super 8.8

Wrong.

The rears are the same, assuming manual to manual or auto to auto. The difference is what the pumpkin is made of. You simply need the 3.15 gears and the carrier from a 3.15 car. Just like you can upgrade a 3.15 geared car to 3.73 with a carrier and gear swap.

TexasRebel · Mar 18, 2018

revtime said:
Wrong.

The rears are the same, assuming manual to manual or auto to auto. The difference is what the pumpkin is made of. You simply need the 3.15 gears and the carrier from a 3.15 car. Just like you can upgrade a 3.15 geared car to 3.73 with a carrier and gear swap.

https://performanceparts.ford.com/download/catalogs/2016/files/assets/basic-html/page-21.html

Guess again.
The carriers are absolutely different for the 3.15:1 ratio.

revtime · Mar 19, 2018

TexasRebel said:
https://performanceparts.ford.com/download/catalogs/2016/files/assets/basic-html/page-21.html

Guess again.
The carriers are absolutely different for the 3.15:1 ratio.

I understand there is a lot of confusion on this matter. And I see you changed your stance from "the 3.15 is not an 8.8" to "the carriers are different". That is correct the carriers are different. I said that in my original post. I am just going to assume you did not comprehend that. All 2015 up Mustangs have the super 8.8 rear. They do, it is, that is a fact. I was simply trying to correct the misinformation that the 3.15 gear cars are not super 8.8. Again, they are.

What the people trying to sell you an 1800 diff are not telling you is that for about 750 bucks you can pretty much put any gear set you want in your current diff.

TexasRebel · Mar 19, 2018

revtime said:
I understand there is a lot of confusion on this matter. And I see you changed your stance from "the 3.15 is not an 8.8" to "the carriers are different". That is correct the carriers are different. I said that in my original post. I am just going to assume you did not comprehend that. All 2015 up Mustangs have the super 8.8 rear. They do, it is, that is a fact. I was simply trying to correct the misinformation that the 3.15 gear cars are not super 8.8. Again, they are.

What the people trying to sell you an 1800 diff are not telling you is that for about 750 bucks you can pretty much put any gear set you want in your current diff.

They all have the IRS rear... The difference between the Super 8.8 and the 8.8 is the pinion & carrier. Which is why the 3.15:1 carrier is not compatible with any other ring & pinion, and nowhere is it ever specified as a "Super 8.8". In fact, if you trust Steeda you'll see that you have to swap the 8.8 carrier on a 3.15:1 to a Super 8.8 carrier to change ratios.

Swapping Diff ratio from 3.55 to 3.15 can it be done

666mac

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