Newbie ? on Gear Ratio

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07gtcs

New Member

Dec 7, 2006

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Dec 18, 2006

#1

• Dec 18, 2006

• #1

My 07 came with Limited Slip 3.31 ratio. Could someone give me a quick explanation on the gear ratio. I understand Limited Slip, but I really don't know about ratios. My guess is that a 3.31 gives you more top speed? and the higher ratio you go will give you more low end???

 

metroplex

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Sep 7, 2003

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SE MI

Dec 18, 2006

#2

• Dec 18, 2006

• #2

double tap

 

metroplex

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Dec 18, 2006

#3

• Dec 18, 2006

• #3

This ratio refers to the ring and pinion gear ratios in the rear end of the vehicle (# of teeth on ring gear divided by # of teeth on pinion gear). There was an optional 3.55 ratio for 07 GTs with the manual transmission. Due to the gearing on the automatic, the 3.31s aren't too bad. The folks with manual transmissions may want to start with the 3.55s for better acceleration from the showroom.

Many owners have upgraded to 4.10s for even faster acceleration.

 

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07gtcs

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Dec 7, 2006

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Dec 18, 2006

#4

• Dec 18, 2006

• #4

metroplex said:

This ratio refers to the ring and pinion gear ratios in the rear end of the vehicle (# of teeth on ring gear divided by # of teeth on pinion gear). There was an optional 3.55 ratio for 07 GTs with the manual transmission. Due to the gearing on the automatic, the 3.31s aren't too bad. The folks with manual transmissions may want to start with the 3.55s for better acceleration from the showroom.

Many owners have upgraded to 4.10s for even faster acceleration.

Click to expand...

Got it...thanks.

 

Power4

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May 10, 2004

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Rochester, NY

Dec 20, 2006

#5

• Dec 20, 2006

• #5

Is there any advantage to having 3.31s over the 3.55s?

 

anthony05gt

Active Member

Mar 18, 2006

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Dec 20, 2006

#6

• Dec 20, 2006

• #6

All '07 GT's have 3.31 gears unless you have the 3.55 option.

 

H

Hoboattacker

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Sep 7, 2005

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Baton Rouge (LSU) / Houston, TX

Dec 20, 2006

#7

• Dec 20, 2006

• #7

Power4 said:

Is there any advantage to having 3.31s over the 3.55s?

Click to expand...

Gas mileage and top end. The lower the gear ratio (do I have that termanology correct?) the more top end and better gas mileage while cruising. Higher ratio means faster acceleration, less top speed, and less gas mileage.

3.31/4.10
top end/off-the-line quick

 

bigcat

start with the upper hole, and if more traction is

May 1, 2005

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7200 feet

Dec 20, 2006

#8

• Dec 20, 2006

• #8

Hoboattacker said:

Gas mileage and top end. The numerically lower (higher gears) the gear ratio the more top end and better gas mileage while cruising. Higher numerical ratio (lower gears) means faster acceleration, less top speed, and less gas mileage.

3.31/4.10
top end/off-the-line quick

Click to expand...

fixed

 

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07gtcs

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Dec 21, 2006

#9

• Dec 21, 2006

• #9

bigcat said:

fixed

Click to expand...

So, 3.31s will give faster acceleration but less gas mileage? Is that correct?

 

metroplex

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Sep 7, 2003

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Dec 21, 2006

#10

• Dec 21, 2006

• #10

07gtcs said:

So, 3.31s will give faster acceleration but less gas mileage? Is that correct?

Click to expand...

If you are comparing 3.31s to 3.27s, 3.08s, or 2.73s then you are correct.
However 3.55s will yield slightly faster acceleration and less gas mileage versus 3.31s. Now if you go to 4.10s, it will yield much better acceleration and theoretically worse gas mileage compared to 3.55s

My Crown Vic has 3.55s from the factory and it SUCKS gas on the highway. At 65 mph, it is turning around 2200 RPM with the torque converter locked. At 75 mph, it is about 2600 RPM w/ the torque converter locked!!

For the 05-up GTs w/ the TR-3650 and 235/55R17 tires:
3.31s
65 mph 1700 RPM
75 mph 2000 RPM

3.55s
65 mph 1800 RPM
75 mph 2100 RPM

4.10s
65 mph 2100 RPM
75 mph 2500 RPM

As you can see, one benefit of a 5-speed transmission is better gearing. However, the TR-6060 in the GT500 yields similar RPM values in the 2nd OD gear (6) as the 5th gear OD in the TR-3650.

FWIW I paid the $87 for the optional 3.55s since I wasn't planning on ever swapping gears or tearing into the rear differential (unless it is to rebuild the T-Lok clutches with the carbon fiber clutches from the 03-04 Cobra). A clutch rebuild doesn't require removal of the ring gear from the carrier or removal of the pinion gear, so 3.55s will work fine for me.

 

Power4

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Dec 21, 2006

#11

• Dec 21, 2006

• #11

Is there a significant difference in gas mileage between the 3.31s and the 3.55s? I can't imagine 100 RPM difference at speed could make that much of a difference. I was planning on opting for the 3.55s when I order my GT in a month but if I could get a couple MPG better with the 3.31s I'd leave it with those (since it'll be my daily driver).

 

metroplex

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Sep 7, 2003

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Dec 21, 2006

#12

• Dec 21, 2006

• #12

I was in the same boat and people said the gas mileage difference between 3.31s and 3.55s was negligible. Note that if you buy the automatic trans, the 3.55s are not available as a factory option. It's only available as a factory option for the TR-3650 manual transmission.

 

iskwezm

10 Year Member

May 24, 2005

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Dec 21, 2006

#13

• Dec 21, 2006

• #13

im going with 4.30's next week. My buddy has them in his 06 auto and got 24 MPG on a recent rtip with his 4.30's.

 

metroplex

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Sep 7, 2003

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Dec 21, 2006

#14

• Dec 21, 2006

• #14

He was probably doing all highway driving at 55 mph... :SNSign: