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Rear Gear


gt5001

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Back in my day (boy, I'm about to sound old here), my *new* Mustang came with a 2.73. How pathetic is that? The AODs had the option of the 3.27, but who wanted an automatic anyhow? LOL! Seriously, I think the 3.31 will be a great all around gear. IMO, a 3.55 would have been a good choice too.

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Consider that rear gearing is a torque-multiplier. The weaker the engine, the more gear you need to provide acceptable acceleration. Ever notice gear ratios on 4-cylinder economy cars? Typically 4.0-6.0 to 1. Most V8's are in the 2.5-3.5 to 1 range as their ample engine torque doesn't need as much of a torque-multiplier in the form of steeper rear end gears.

 

That said, most guys who built muscle cars tend to put a lot of gear (4.10's to 4.56's) in a naturally aspirated high horsepower car. However, guys who build cars with superchargers (with their far superior torque) tend to run less gear. In 5.0 or 4.6 Mustangs, the most common gear used with a supercharger is a 3.55 or even 3.27. More gear than 3.55 is a waste as you don't really need the extra torque-multiplication. In fact, going with 4.10's or steeper with a blower actually will slow you down at the track as you'll be out of the peak torque curve too quickly.

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QUOTE(Five Oh B @ Mar 11 2006, 08:03 PM) 4892[/snapback]

Consider that rear gearing is a torque-multiplier. The weaker the engine, the more gear you need to provide acceptable acceleration. Ever notice gear ratios on 4-cylinder economy cars? Typically 4.0-6.0 to 1. Most V8's are in the 2.5-3.5 to 1 range as their ample engine torque doesn't need as much of a torque-multiplier in the form of steeper rear end gears.

 

That said, most guys who built muscle cars tend to put a lot of gear (4.10's to 4.56's) in a naturally aspirated high horsepower car. However, guys who build cars with superchargers (with their far superior torque) tend to run less gear. In 5.0 or 4.6 Mustangs, the most common gear used with a supercharger is a 3.55 or even 3.27. More gear than 3.55 is a waste as you don't really need the extra torque-multiplication. In fact, going with 4.10's or steeper with a blower actually will slow you down at the track as you'll be out of the peak torque curve too quickly.

 

 

On a stock Cobra with the weaker torque 32V the 4.10 is the way to go. 3.73 is less better. With a SC or Turbo 3.73 is max I suppose.

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I agree with both of you. Great explanation! :bowdown:

 

This should further illustrate your point:

 

In my '95 GT, I run a 4.10. The car is a street/strip car, doesn't see much highway (or driving in general for that matter). With the cams we tens to choose for this car, 4.10s were the only way to go. The car is, was, and always will be naturally aspirated. It's a 5 speed.

 

In my husband's '95 GT, he runs a 3.55 gear, and frankly, I think that's about as much as the car could handle. He runs a Kenne Bell 1500 with 8 psi. The car is "tractionally challenged" even with the smaller gears. I feel the 3.73s would be way too much for his car. His is also a 5 speed.

 

*If* we had a n/a 4.6L, on the other hand, I'd definitely go with a 4.10. My reasoning is totally different than that of the '95, but from what I've seen, the 4.6 just LOVES the steep gears.

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I agree with both of you. Great explanation! :bowdown:

 

This should further illustrate your point:

 

In my '95 GT, I run a 4.10. The car is a street/strip car, doesn't see much highway (or driving in general for that matter). With the cams we tens to choose for this car, 4.10s were the only way to go. The car is, was, and always will be naturally aspirated. It's a 5 speed.

 

In my husband's '95 GT, he runs a 3.55 gear, and frankly, I think that's about as much as the car could handle. He runs a Kenne Bell 1500 with 8 psi. The car is "tractionally challenged" even with the smaller gears. I feel the 3.73s would be way too much for his car. His is also a 5 speed.

 

*If* we had a n/a 4.6L, on the other hand, I'd definitely go with a 4.10. My reasoning is totally different than that of the '95, but from what I've seen, the 4.6 just LOVES the steep gears.

 

 

Right said, Michelle.

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  • 8 months later...

This table show the RPM's in the first position and the speed for each gear.

 

3.73

6500 - 47, 78, 106, 138, 173, 219

 

3.90

6500 - 45, 74, 102, 132, 165, 210

 

4.10

6500 - 42, 71, 97, 126, 157, 200

 

Tire Dia. 26.66

 

1st = 2.97

2nd = 1.78

3rd = 1.30

4th = 1.00

5th = .80

6th = .63

 

Link to the calcutator.

 

Personally, I will be going with 3.90's. They will be the best for what I have planed.

 

Good luck with your selections,

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B)-->

QUOTE(Five Oh B @ Mar 11 2006, 02:03 PM) 4892[/snapback]

Consider that rear gearing is a torque-multiplier. The weaker the engine, the more gear you need to provide acceptable acceleration. Ever notice gear ratios on 4-cylinder economy cars? Typically 4.0-6.0 to 1. Most V8's are in the 2.5-3.5 to 1 range as their ample engine torque doesn't need as much of a torque-multiplier in the form of steeper rear end gears.

 

That said, most guys who built muscle cars tend to put a lot of gear (4.10's to 4.56's) in a naturally aspirated high horsepower car. However, guys who build cars with superchargers (with their far superior torque) tend to run less gear. In 5.0 or 4.6 Mustangs, the most common gear used with a supercharger is a 3.55 or even 3.27. More gear than 3.55 is a waste as you don't really need the extra torque-multiplication. In fact, going with 4.10's or steeper with a blower actually will slow you down at the track as you'll be out of the peak torque curve too quickly.

 

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This table show the RPM's in the first position and the speed for each gear.

 

3.73

6500 - 47, 78, 106, 138, 173, 219

 

3.90

6500 - 45, 74, 102, 132, 165, 210

 

4.10

6500 - 42, 71, 97, 126, 157, 200

 

Tire Dia. 26.66

 

1st = 2.97

2nd = 1.78

3rd = 1.30

4th = 1.00

5th = .80

6th = .63

 

Link to the calcutator.

 

Personally, I will be going with 3.90's. They will be the best for what I have planed.

 

Good luck with your slections,

 

This is very close to the spreadsheet model I posted about a week ago. It's an Excel file if anyone is interested, but I would have to email it rather than post it.

 

Dave

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Mik, Alloy,Lambo ,We just have lots of clutch shudder starting out with the 3.31s. I think the 3.73 or 3.90 probably would solve. I think it would still be plenty managable with those gears, Rain might, nail ya with a gotcha. Lambo, how's the 3.31s stack up against the deeper gears on your graph?? wh

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Mik, Alloy,Lambo ,We just have lots of clutch shudder starting out with the 3.31s. I think the 3.73 or 3.90 probably would solve. I think it would still be plenty managable with those gears, Rain might, nail ya with a gotcha. Lambo, how's the 3.31s stack up against the deeper gears on your graph?? wh

 

 

Here ya go Wh, I included the low end as well. 500-1000 RPM

 

3.31

6200 - 50, 83, 114, 149, 186, 236

500 - 4, 7, 9, 12, 15, 19

600 - 5, 8, 11, 14, 18, 23

700 - 6, 9, 13, 17, 21, 27

800 - 6, 11, 15, 19, 24, 30

900 - 7, 12, 17, 22, 27, 34

1000 - 8, 13, 18, 24, 30, 38

 

3.73

500 - 4, 6, 8, 11, 13, 17

600 - 4, 7, 10, 13, 16, 20

700 - 5, 8, 11, 15, 19, 24

800 - 6, 10, 13, 17, 21, 27

900 - 6, 11, 15, 19, 24, 30

1000 - 7, 12, 16, 21, 27, 34

 

3.90

500 - 3, 6, 8, 10, 13, 16

600 - 4, 7, 9, 12, 15, 19

700 - 5, 8, 11, 14, 18, 23

800 - 5, 9, 13, 16, 20, 26

900 - 6, 10, 14, 18, 23, 29

1000 - 7, 11, 16, 20, 25, 32

 

4.10

500 - 3, 5, 7, 10, 12, 15

600 - 4, 7, 9, 12, 15, 18

700 - 5, 8, 10, 14, 17, 21

800 - 5, 9, 12, 15, 19, 25

900 - 6, 10, 13, 17, 22, 28

1000 - 7, 11, 15, 19, 24, 31

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Here ya go Wh, I included the low end as well. 500-1000 RPM

 

3.31

6200 - 50, 83, 114, 149, 186, 236

500 - 4, 7, 9, 12, 15, 19

600 - 5, 8, 11, 14, 18, 23

700 - 6, 9, 13, 17, 21, 27

800 - 6, 11, 15, 19, 24, 30

900 - 7, 12, 17, 22, 27, 34

1000 - 8, 13, 18, 24, 30, 38

 

3.73

500 - 4, 6, 8, 11, 13, 17

600 - 4, 7, 10, 13, 16, 20

700 - 5, 8, 11, 15, 19, 24

800 - 6, 10, 13, 17, 21, 27

900 - 6, 11, 15, 19, 24, 30

1000 - 7, 12, 16, 21, 27, 34

 

3.90

500 - 3, 6, 8, 10, 13, 16

600 - 4, 7, 9, 12, 15, 19

700 - 5, 8, 11, 14, 18, 23

800 - 5, 9, 13, 16, 20, 26

900 - 6, 10, 14, 18, 23, 29

1000 - 7, 11, 16, 20, 25, 32

 

4.10

500 - 3, 5, 7, 10, 12, 15

600 - 4, 7, 9, 12, 15, 18

700 - 5, 8, 10, 14, 17, 21

800 - 5, 9, 12, 15, 19, 25

900 - 6, 10, 13, 17, 22, 28

1000 - 7, 11, 15, 19, 24, 31

 

 

hmmm pretty close to what I found while trying to check my top speed as ran in 5th gear.

 

a bit past 5750 rpm probably closer to 5800.

 

Are those numbers rounded at all? I measured tire size and figured my top speed was 170mph plus. This shows it to be 172.5+ mph. Do you know what the tire growth on these tires are?

 

Speedo stopped dead right at 160... Did not realize there was a speedo needle stopper there.

 

Noticed a bit of hood flutter once I hit 160. Even at 170+ car ran dead straight

 

Was the 3.31 rear gear expected? Or, with the 6-speed is that OK?

 

 

 

Should have kept my comment to topic

 

I love the 3:31 gearing and would not consider changing it in either car. Adding another 100hp maybe but no gear change for me.

 

Because the Shelby has a different ring gear mounting method from factory I can assume most having gears changed are not doing the same. If not your Warranty will be void on rear end.

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