3.31 vs 3.73 gear ratio - Mustang Evolution

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Old 12-29-2013, 07:02 PM   #1
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3.31 vs 3.73 gear ratio

What's the difference between these 2 on a 2014 GT? I was advised by a Ford Racing engineer to install a 3.73 to increase take off from a full stop.
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Old 12-30-2013, 02:21 PM   #2
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Mine has 3.31 or that's what it says on the pumpkin but I bought it used with 15K on it. I take off like a raped ape and 3rd gear barks are very easy. Someone may have changed my gears, I wish I could figure out a way to tell. 3.73 will get you off the line faster but if you are on street tires, it wont help much because its hard to put the power to the road anyway. Thats just me though. Other people may think different.
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Old 12-30-2013, 03:26 PM   #3
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Quote:
Originally Posted by Green5.0 View Post
Mine has 3.31 or that's what it says on the pumpkin but I bought it used with 15K on it. I take off like a raped ape and 3rd gear barks are very easy. Someone may have changed my gears, I wish I could figure out a way to tell. 3.73 will get you off the line faster but if you are on street tires, it wont help much because its hard to put the power to the road anyway. Thats just me though. Other people may think different.
I have the 3.73 on my 2014 GT. It runs 2400 rpm in 6th gear at 80 mph. You can compare to that to see if you have the 3.31 or the 3.73.
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Old 12-30-2013, 11:52 PM   #4
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I have 3.73 and it's fun but, it isn't worth the expense to switch from 3.31 to 3.73. It's a cheap option tick new but, not so much after the fact.

Little things: 3.73 factory rears come with GT500 carbon clutch LSDs. Others come with fibre plate LSDs.

Little headaches: You switch to a 3.73 rear, you have to take it to Ford to reset the computer for the new gear. Even though it's a 5 minute setting switch in Ford IDS, they'll no doubt bill you for it.
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Old 12-31-2013, 06:15 AM   #5
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Thanks bryan, I will check my rpms today!
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Old 12-31-2013, 10:43 AM   #6
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I've got a 12 GT and it came 3.31 but I swapped mine for 3.73's. I had to work with it to get the shims just right so it wouldn't whine but now that it's done, it was a satisfying mod. I've got a Steeda Boss Manifold power package along with some susp mods, the rpm comes on faster of course which translates to either forward motion, wheel spin, or a combo... My very next mod is some American Racing VN427 rims and some fat drag radials in the rear! Lastly, your tuner can adjust rear gear ratio thru like an SCT tuner, Ford will charge you a good bit for either a gear swap or even the ECU work. Good luck either way ya go!
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Old 12-31-2013, 06:26 PM   #7
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In a manual, yes good upgrade or even 4.10s. In an auto stay with the stock gears.
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Old 01-01-2014, 07:50 PM   #8
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Quote:
Originally Posted by Green5.0 View Post
Mine has 3.31 or that's what it says on the pumpkin but I bought it used with 15K on it. I take off like a raped ape and 3rd gear barks are very easy. Someone may have changed my gears, I wish I could figure out a way to tell. 3.73 will get you off the line faster but if you are on street tires, it wont help much because its hard to put the power to the road anyway. Thats just me though. Other people may think different.
To find your gear ratio, there's only one way to do it right. For get about rpms this or that. Jack the rear on jack stands. Mark the bottom of your tire and the bottom of the drive shaft. Turn the wheel one complete rotation while counting how many times the drive shaft turns, this will give you the ratio.

Examples
3.31= a hair over 3 an a quarter turns.
3.73= 3 an 3/4 turns.
4.10= a hair over 4 turns.
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Old 01-02-2014, 01:08 PM   #9
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3.31= a hair over 3 an a quarter turns.

3.73= 3 an 3/4 turns.

4.10= a hair over 4 turns.

+1.... Exactly what I was about to post
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Old 01-02-2014, 01:45 PM   #10
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I have heard that and forgot about it. I will have to check some day.
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Old 01-02-2014, 01:51 PM   #11
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You can figure it out using the door tag and rpm to a pretty high degree of certainty, without the effort of jacking the car up.

5th is 1:1 on these cars and takes the transmission ratios out of the equation.

Look at the door tag for axle code and google it.

Then drive highway at 60 mph in 5th, on cruise preferably. You'll have previously thrown the numbers for your door tag ratio into any one of 100 gear ratio calculators online and you'll see if it's right or if someone has changed things. Based on what you find a 60 mph, you can work backwards if you find any changes made.
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Old 01-02-2014, 09:29 PM   #12
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Quote:
Originally Posted by 5LHO View Post
You can figure it out using the door tag and rpm to a pretty high degree of certainty, without the effort of jacking the car up.

5th is 1:1 on these cars and takes the transmission ratios out of the equation.

Look at the door tag for axle code and google it.

Then drive highway at 60 mph in 5th, on cruise preferably. You'll have previously thrown the numbers for your door tag ratio into any one of 100 gear ratio calculators online and you'll see if it's right or if someone has changed things. Based on what you find a 60 mph, you can work backwards if you find any changes made.
Except that if his speedometer is off it won't be right. You can always use a GPS I suppose. It takes all of 10 minutes to jack the *** end of the car up and spin the tires.
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Old 01-02-2014, 10:55 PM   #13
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I suppose it's possible somebody jacklegged an install and didn't do the proper correction but it's pretty likely theres a factory gear in there, really, if we are playing the odds on a relatively new car
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2012 Premium GT, Candy Red, Brembo package, 3.73, MT82, Comfort, Tech, et al. Procal tune, Roush UCA, UMI poly LCA, GT500s, Steeda red bracket, Hoosier 28x10x16 bias drags. Best e/t 11.91 at 115.23 RIP
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Old 01-03-2014, 07:03 AM   #14
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Yeah I'm assuming this 2014GT is bought new in which case the door sticker will obviously be right. Just saying that for a car that someone had prior to the previous owner you never trust any method except the wheel turn method mentioned here.
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