Earlsays

I have a 2014 GT automatic with 3.15 rear gears. I would like to go to 3.73 or 4.10 - however, I want to keep the factory computer tune - programmers make me nervous due to potential warranty cancellation.

Is there any way to change rear gears, have speedometer and odometer accuracy, correct shift points, and NO aftermarket computer tune?

GrabberBlue5.0

No their isn't and a gear change to those gears will not make your car any faster. You already have 3.55-3.60 gearing when you do the math with the gears in the transmission.

AlsCobra

And exactly how does this statement make any sense whatsoever? Would this be a comparison to the M/T with 3.55's? I truly wish you could "do the math" before you continually fill these boards with opinionated and second hand bad advise.

Moejoe_989

I am only offering a suggestion here, and someone please correct me if I'm wrong but; I was under the impression that if you take those gears to your Ford dealer, as long as they are a OEM spec gear ratio: 3.15, 3.31, 3.55, 3.73, or 4.10, they can install those gears, and can and will do the speedo correction for you? They HAVE to correct your speedo (I'm assuming)
Should be able to be fairly quick and painless and keep everything your looking for.

Little off topic but: Did I read somewhere that Ford doesn't offer anything higher than a 4.10 for these mustangs anymore? Is that correct?

Moejoe_989

I'm pretty ignorant on the topic as I've never done a gear change before, but I did a little bit of reading and thought there might be some useful information here.

Seems that Ford can't properly adjust for a gear ratio steeper than 3.55's. (3.73's and 4.10's) unless they re flash your ECC. But, I'll let you guys read the thread and come to your own conclusions. I don't wanna say things that aren't true or misinformed.

http://forums.corral.net/forums/gt-s.../topics/265592

dmhines

Keep in mind when changing gears in an auto it could affect your gear shift points as well. Even if dealer can change gear ratio they can't reprogram transmission.

GrabberBlue5.0

I'll explain very simply as I have a ton of first hand experience here while you don't even own one of these cars. Now following along real close. And FYI these cars come with the 6R80.

Consider these first gear ratios:

C4 - 2.46
4R70W - 2.84
6R80 - 4.17

Take the 4.17 and multiply it by the 3.31, you get 13.8 for an overall gear ratio in 1st. Now take that 13.8 and divide it by the first gear ratios of the other transmissions and this tells you what axle ratio would give you the equivalent with those transmissions:

C4 - 5.61
4R70W - 4.86

So, although 3.31 "sounds like" not much gear, you can see that in the end, it is quite a bit of gear with the 6R80.

We can do the same with the second gear ratios:

6R80 - 2.34
C4 - 1.46
4R70W - 1.55

That puts the 6R80/3.31 at 7.75, which is like a 4R70W with a 5.00 axle, or a C4 with a 5.31 axle.

And finally 3rd gear, where the 6R80 is 1.52*3.31=5.03, the others are 1 to 1, so 5.03 would be the equivalent axle there.


You'd all agree that an axle in the 5.00 range is a lot of gear, well, we're doing exactly the same thing with the 3.31/6R80, we just have 3 more gears to go after that.


Going the other way, a 4.10/6R80 in first gear is like having a C4 with a 6.95 gear, or a 4R70W with a 6.02 gear. You can see why hooking it is a problem.

Earlsays

Interesting. Thanks. So, why does my car lack that "seat of the pants" feeling of speed?

GrabberBlue5.0

Two things. The autos really wake up with a tune and the stock converter only flashes to 1800 rpm. I know you said a tune is not something you want to do at this point but it makes a night and day difference. Just a tune alone and you'll be spinning your tires at will and then will realize the gears were not a detriment. Trust me on this. I've been 11.2 @ 122 mph N/A and still on stock 3.15's. And there are a lot faster guys out there than me.

Earlsays

I have run tuners in the past - they're great, I don't have a problem with them, I just worry about the powertrain warranty

AlsCobra

You truly have the most dizzying sense of reason I've ever seen. All this you've just typed is complete nonsense and just a general comparison to first gear in a different transmission. Yes first is very low compared to most transmissions but in comparison, the rest of the gears are very close and 4th seems like a very good pulling gear.

GrabberBlue5.0

Again you don't even own one of these cars but are a complete expert? I think I've made my point as most will note. You do not want the car shifting into 4th before you cross the stripe. That's why all the fastest autos are running a 3.15-3.31 gear. It's not coincidence.

AlsCobra

Secondly here you have said on more that none occasion, that I have no first hand experience and I don't own one so I can't know what I'm talking about. I know hp. I know racing. I know gearing. This is not some type of unicorn vehicle that reacts completely different from every other vehicle in history.
Your car does very well for the lack of power you actually have. If your car shifts into 4th, you lose power because of what rpm your car makes power. So lower gears and using 4th can't help
You any until you can add a lot more hp/tq. So lowering a ratio on a stock or slightly modded auto GT will not improve ET in a quarter, sometimes people don't race 1/4 and it will help out in those cases.

AlsCobra

No you made a lot of bad statements that are simply untrue all over this forum. I just can't tolerate wrong advise being spewed all over the place. I've said this already that your car runs really good times for your particular setup. I'm sure you've copied your setup from a bunch of other people on the internet also. But don't go telling everybody that 3.15 gears is the best gear for drag racing their car. It's just the better gear when you're not making horsepower. I really hope the members here are not believing anything you post here. Really hope they don't fall for your expert opinions.

Earlsays

Jeez you guys, I really did not intend to start any arguments- everybody needs to chill...just lock this thread, obviously nothing positive is happening within this discussion.

GrabberBlue5.0

You can either listen to the guys that have and race these cars with success or the guys that are keyboard racers only. PM if you want for any advice as I've been dealing with these cars for years now. I won't steer you in the wrong direction.

tom281

To answer your question the only way I know of to correct the speedo/odo without using an aftermarket tune is to have the dealer modify the factory tune for the new gear combo. I would think that you'd find some dealers willing to do this for minimal charge and no hassle and other dealers threatening that altering the tune and/or changing the rear gear would void the power train warranty. Depending on their prerogative.

AlsCobra

I'm sorry buddy. This is a continuation of this guy going to every thread asking about gears and stating you don't need them. Gears will make your ride a lot more fun. Go for it.