Gearing for 2015 GT

[doughboy305]

Hello all I'm new to this forum and had a few questions for you guys I purchased my car about a lil under a year ago I am running a Bama Tune and JLT cai i have a set of 373 gears to put in the car currently have the 315 that came with car. I have heard I shouldn't make this change. I would like some input as to why or why not to install the gears and if so I heard the computer cannot be calibrated for the 3.73 gear is this still true any help would be appreciated.

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[LETHAL]

PP cars come with 3.73s so it obviously can be done.

 

[doughboy305]

Sorry Forgot to mention its a auto car

 

[Five Oh Brian]

I sure hope that gear swaps can be simplified for the S550 crowd. I love the 4.10's in my '14 GT Automatic. I love the big stall converter in the 6R80 trans even more. 3.15 gears and a stock converter just don't cut it for me.

 

[MagGT]

from my understanding, the 3.15 gears in the auto are actually more aggressive in first gear and maybe second but are much more lax in the later ones so switching to the 3.73 that are for the manuals are actually worse for autos.

This comes from some knowledge on this board. not sure if too accurate tho.

 

[jasonstang]

3.73 on the auto is gonna be ridiculous in 1st gear.

 

[timd38]

3:73 will definitely make it more perky. I read on here someplace that the diff housing for the 3:15 is different than than 3:55 and 3:73. You can get 3:55 with an auto trans, so maybe that would be a better gear choice.

 

[Chameleon]

Look at 3.55's if you have an auto.

 

[2015 Silver GT]

You would need to purchase the Whipple flare tool to make the necessary changes. Also the housing is different so you can't just change the gears. In the end it would be pointless since it's already been shown on these cars the 3.15's are faster in the auto over 3.73's. Seems like a lot of money wasted to make your car slower.

 

[hiccup]

I have to agree with them.go 3:55..Id say theres a good reason Ford limited the auto to those as the optional gear

 

[Burnin4]

I'm knee deep in swapping my 3.15's for 3.55's in my auto. I'm pretty sure my rear diff is toast and there are zero options to upgrade the differential with 3.15's/aluminum housing. I purchased a new cast iron differential housing as well as the seal/bearings, Weltrac differential and a 3.55 ring & pinion next.

I'm really curious how this swap will affect my et's/mph. I really liked my 3.15's but don't want to replace with just another stock unit. Pretty disheartening that there are no options to upgrade a 3.15.

 

[doughboy305]

I'm knee deep in swapping my 3.15's for 3.55's in my auto. I'm pretty sure my rear diff is toast and there are zero options to upgrade the differential with 3.15's/aluminum housing. I purchased a new cast iron differential housing as well as the seal/bearings, Weltrac differential and a 3.55 ring & pinion next.

I'm really curious how this swap will affect my et's/mph. I really liked my 3.15's but don't want to replace with just another stock unit. Pretty disheartening that there are no options to upgrade a 3.15.

why is your diff toast

 

[VinnAY]

from my understanding, the 3.15 gears in the auto are actually more aggressive in first gear and maybe second but are much more lax in the later ones so switching to the 3.73 that are for the manuals are actually worse for autos.

This comes from some knowledge on this board. not sure if too accurate tho.

What you say there has nothing to do with the rear gear...how is a static ratio of 3.XX more aggressive in first, and maybe second...that's everything to do with the trans gear ratio(s).

 

[Burnin4]

why is your diff toast

My diff is peg legging during burnouts at the strip, one wheel at a time is spinning instead of both. I've done 30+ line lock burnouts at 650'ish on with heavy 20's and MT's. She still drives fine but don't think she's gonna last very much longer.

I really want to keep my 3.15's because I can stay in 3rd till 140mph, and my trap speeds are 135+. If I install 3.55's then I gotta shift into 4th at 124mph, the extra shift might cause me to lose et. The problem is, there are no aftermarket upgrades for the 3.15 diff, only 3.55+, and the entire project is well over $2000 for the new cast iron housing, gaskets/seals/bearings, right and pinion, Weltrac diff, Whipple Flare tool, and labor. All that to possibly go slower....

 

[silver.gt]

I also have the 3.15 with 20" wheels on my car, I would like to know the pros of going up to 3.55. Will my car be faster or will it only feel faster?
I like my 3.15 because it's easy to launch but I do feel some time it does need a little bit more of jump from the get go or when try to have fun like doing donuts or trying to just fish tail the rear a little and I that with the 3.15 you need to add more gas the I would need to with 3 the 3.55.
Also does having 20" wheels and 3.15 make me slower then some one with 18" wheels and 3.15?

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