I'm a newbie to engines and stuff but I'm trying to learn. My GT has a 3:31 Rear Axle Ratio. I have seen options for a 3:55 and 3:73. Several shops have said I could put a 3:73 Gear ratio in it and it would run faster. My 1st question is, what do these numbers mean? My 2nd question is, would a 3:73 work in a 06 GT Convertible? I have been on Ford's website and configured a couple of new GTs. The convertibles are always ONLY available with a 3:3I, even with a Shelby.

 

The Same applies to mustangs with automatic transmissions. I guess that convertibles and automatics don't have the option to be equipped with a 3:73 ratio because Ford probably figures that anyone who gets an automatic or convertible mustang may care about ride comfort and convenience more than racing. 3:31 gears are better on the highway (cruise at lower RPM) and they don't pull as hard in accelerating.

The rest of your question is too complicated for me to answer correctly.

 

Oh Yeah, the 3:73 gears will work on a convertible and automatic transmission. Also, you will either have to tune your car with an SCT tuner or you will have to buy a recalibration thingy (that ford racing makes) in order for your speedometer to correctly display your speed........and that's if you change your gears.

 

For example, 3:73 gears means for each time your rear axle does one complete rotation, your driveshaft goes around 3:73 times. Get it?

 

The gear ratio, 3.31, for example, means that when your driveshaft turns 3.31 times, you only get 1 revolution of your tire. The ratio is best written as 3.31:1, which literally means 3.31 driveshaft turns to get only 1 turn of your tire.

Therefore, 3.73 (3.73:1) means 3.73 driveshaft turns to get only 1 turn of your tire.
4.10 (4.10:1) means 4.10 drivestaft turns to only get 1 turn of your tire.
6.00 (6.00:1) means 6 driveshaft turns to only get 1 turn of your tire.

As far as faster with a numerically higher gear (for example replacing your low geared 3.31 with a higher gear 3.73) does not mean faster in every respect. You have to consider what your definition of fast is.
There is fast as in faster acceleration.
And there is fast as in much higher top speed.

Lets us assume no air resistance (i.e. aerodynamics is not a factor)
If you go with a numerically higher gear (replacing your 3.31 with a 3.73), you will go faster as far as acceleration does, but you will LOSE maximum potential top speed.
If you keep your 3.31 gear, you have a higher potential top speed than with the 3.73, BUT you will not accelerate as fast.

You have to consider which "fast" you want when you choose your rear gears. Acceleration? Or faster potential top speed?

 

3.90s or 4.10s. 3.73 aren't worth the money vs performance

 

I 100% disagree.

I went from 3.31s to 3.73s and it's noticeable quicker. I considered a steeper gear for a while but am glad I chose what I did. I do some highway driving and feel that 4.10s would be too much, but they would be a great street gear. The 3.73s are a good compromise IMO if you want highway/street performance

 

That is correct. And another thing you have to consider is what is the gear ratio of your tranny's 1st gear?
For example, an aftermarket T56 Magnum has a 2.97:1 1st gear (if you get the wide ratio T56).
Compare that to the TR3650 1st gear of 3.38:1.

Slap on a 4.10:1 rear gear on a T56 and you get a total final gear ratio of 12.17:1
A stock TR3650 with 3.31 rear gear in 1st gear gets a total of 12.58:1, which is actually better than the T56 with the 4.10!
The stock TR3650 and stock rear gear actually has better acceleration potential than a T56 with 4.0!

Now, put a 4.10 on a TR3650 and you get a sick 1st gear total ratio of 15.58:1!!!!
Now, that makes for way excellent torque multiplication and a much better advantage at the line form a dead stop on the drag strip!

 

My new edge with a t45 revs at 2200 at 70 mph with 3.90s. I drove both 3.73s and 4.10s in a new edge and I could barely notice a difference with the 3.73s and the 4.10s are crappy in city. I am happy with my gear choice in this particular car however I have no experience with other models. And my mileage went up across the board with this gear in. I assume because it takes less pedal pressure to get to and maintain speed. To each their own tho. Any gear is an improvement over stock

 

WOW if tossing in some 3.90's gives better performance AND improves fuel economy, that's awesome!!

WTF was Ford thinking not doing this right at the factory? They must be retarded or something!