3.73 vs 4.10 for Auto

[Beerus]

Hello there, i'm wanting to change my gear ratio for my 2007 ford mustang 4.6 3v Auto but i don't know which one i want and would be best for my car so thought id ask for peoples experience and stats on what they got out of them as i can't seem to find the answers i'm looking for.

First of all my car is all NA and these are the modification's on it currently

Cold Air Intake Kit
Ford Performance Fuel Injector Set 24Lb EV6
Walbro High Performance Fuel Pump Kit 400 LPH
MSD Ignition Coil Packs
Runners Delete
Straight Piped and Decat

This car is my daily and so i'm not bothered for fuel economy, gas milage etc, my goal really is to go from 0 to 120mph as fast as i can but if i can make it go from 0 to 140mph or 150mph or more is a bonus as i don't want to sacrifice too much of my top end, i want the car to overtake cars alot more faster and easier if i need to overtake and also want to set off faster as well, especially on a roll. I used to drive really hard till i blew up my last engine and i been alot more tame but i still like to give it some shit when i want to, i drive way more sensible now compared. also my gearbox is fully been rebuilt as well so practically new inside.

I want to know everyone else's opinion on what would be best for me, the stats on what top speed you got on 3.73 and 4.10 gears roughly, rough times etc, or if you got videos i can watch would help a ton as well as it gives me an idea visually what to expect, some people say 3.73 barely does anything different and makes the gearbox shifting harder n stiffer, some say 4.10 is best for auto because it makes the biggest difference but gear changes can be overwhelming for the gear box and late shifts etc, some say you need a tune for the gear ratios some say not, i have no clue how true all this is but i want the best i can get out of my car,

Many Thanks

 

[86GT351]

A 3.73 gear ratio offers better highway fuel economy and lower engine RPMs, while a 4.10 gear ratio provides stronger acceleration and torque, though at the expense of lower top-end speed and higher engine speeds at cruise. The choice depends on driving style: 3.73 is better for a daily driver with highway cruising, whereas 4.10 is preferable for performance-oriented vehicles, especially those with large tires or heavy loads.

3.73 Gear Ratio

• Pros:
  • Better Fuel Economy: Lower engine RPMs at highway speeds contribute to improved fuel efficiency.
    
    
  • Quieter Operation: The engine runs at lower speeds, resulting in a quieter, more relaxed driving experience on the highway.
    
    
  • Higher Top-End Speed: The vehicle can achieve higher speeds before hitting the engine's redline.
    
• Cons:
  • Slower Acceleration: Less torque is applied to the rear wheels, leading to slower initial acceleration compared to 4.10 gears.
    

4.10 Gear Ratio

• Pros:
  • Increased Acceleration: More torque is delivered to the rear wheels, resulting in quicker off-the-line performance and faster acceleration.
    
    
  • Better Towing and Hauling: The increased torque is beneficial for towing heavy loads or for off-road applications.
    
• Cons:
  • Reduced Top-End Speed: The engine will reach its redline at lower speeds, limiting the vehicle's overall top speed.
    
    
  • Higher Fuel Consumption: Increased engine RPMs at cruising speeds can lead to lower fuel economy.
    
    
  • Increased Engine Strain: The engine works harder at lower speeds, potentially leading to higher oil temperatures.
    

How to Choose

• For a daily driver or highway cruiser:
  A 3.73 gear ratio is generally a good choice, offering a balance of performance and fuel efficiency.
  
  
• For performance, towing, or heavy use:
  A 4.10 gear ratio is better if you prioritize quick acceleration, have larger tires, or frequently tow heavy loads.

 

[Laga]

With the 3.73 gears, your top end is going to be 134mph with a stock 55R5.
I have an 05 with aftermarket SC. A few years ago, I took my car to a “No Fly Zone” speed event where the cars can run flat out for a 1/2 mile. At the end, there is a speed trap to measure how fast you are going. I ran 4 times, and with 3.73 gears, my top end was 133 through 135mph.
4.10 gears will give you a slower top end.

 

[07 Boss]

Rear tire size will make a difference with your final drive ratio. I have 4.10s but run an almost 29" tire which drops my effective ration down to like 3.83 or something like that.

 

[whitmanink]

im gonna chime in as i just put ** 4.10*** in my 5 speed

altho mine is a 5 speed and your is auto , im sure some things will differ

i got a taller tire and a 305 wide tire in the rear so that plays a roll in everything as well..

** from a start your gonna spin unless you get the rear end beefed up ..

****the top speed i have no clue,, (in mexico i was over 138mph and still had quite a bit to go on the rev range but that was fast enough for me so i backed off)

****im not sure about the engine strain at lower rpm , as the gears move everything higher in the rev range? im sure you can still "lug" the engine ,, but you can with any gear combo?

*** obviously MPG will go down ,, depending how you drive (i have a93 tune and mine isnt a DD)

*** you will be the fastest with 4.10 (providing you have the traction)
the 4.10 will keep you in the power band for the most part when racing,
whereas the 3.73 will get you lower in the rev range with each electronic shift thus giving you less hp at the beginning of every shift ,thus making you slower

****engine wear will be more because you are reving higher ,thus moving faster and so on.. but not like some will say ..

but with 4.10 im gonna say ,,tires and control arm relocation brackets and good bushings in the rear ,, are mandatory for 4.10,, unless you just want to spin.

so that adds to cost

 

[Beerus]

Thanks all, you all have given me a good idea what to expect. Can anyone tell me how much mph does the speedo go out? I heard it knocks your speed out alot

Many thanks

 

[whitmanink]

Thanks all, you all have given me a good idea what to expect. Can anyone tell me how much mph does the speedo go out? I heard it knocks your speed out alot

Many thanks

enough.... you will definitely need a sct or similar to change that value in the ecu

 

[Pentalab]

I have a 2010 GT auto (4.6L) with the same 5r55S auto tranny.....plus small Roush M90 blower, and a ton of suspension mods.
Mine came with the oem 3.31 rear gear. Top speed in 4th gear is 150 mph @ 6 krpm. With a 4.10 rear gear, top speed is 121 mph @ 6 k rpm. (3.31 / 4.10) = .807
.807 x 150 mph = 121 mph.

So if you want to be going 140-150 mph you will have to be in 5th (OD) if a 4:10 rear gear is used....and that will be a tough slog from 120 to 150 mph in OD.

I left the oem 3.31 rear gear alone. Here's why. 2nd gear on the 5r55s is already 14% lower than 2nd gear in the manual tranny. The manual tranny would require a 3.73 rear gear to equal the 3.31 rear gear in the auto tranny.

3rd gear in the auto tranny is 16.5% lower than the 3rd gear in the manual tranny. You would need a 3.90 rear gear on the manual tranny to equal the 3.31 rear gear.

Where I lose it is in 4th gear, with my 3.31 rear gear. Both the auto and manual tranny are a 1:1 transmission ratio. And if the manual tranny has a 3.55/3.73/3.90/4.10 rear gear, it will accelerate faster....albeit with a successive lower top speed.

My rears are only 27.4" tall.

It's a bunch of tradeoff's. I have 390 rwhp and 370 rwtq with my small blower, so acceleration is ample for my needs.

 

[JC SSP]

What I have noticed in my years of building and racing cars… forced induction or power adders like lower taller numerical gears (3:31) and N/A likes shorter higher numerical gears (4:10).

Case in point, buddy had a 87’ Firebird Formula with 383 stroker and 200HP juice and 700R automatic. He went from stock 3:27 to 3:90. On motor it ran a little quicker but with juice ran slower. He went back to the 3:27.

 

[whitmanink]

I have a 2010 GT auto (4.6L) with the same 5r55S auto tranny.....plus small Roush M90 blower, and a ton of suspension mods.
Mine came with the oem 3.31 rear gear. Top speed in 4th gear is 150 mph @ 6 krpm. With a 4.10 rear gear, top speed is 121 mph @ 6 k rpm. (3.31 / 4.10) = .807
.807 x 150 mph = 121 mph.

So if you want to be going 140-150 mph you will have to be in 5th (OD) if a 4:10 rear gear is used....and that will be a tough slog from 120 to 150 mph in OD.

I left the oem 3.31 rear gear alone. Here's why. 2nd gear on the 5r55s is already 14% lower than 2nd gear in the manual tranny. The manual tranny would require a 3.73 rear gear to equal the 3.31 rear gear in the auto tranny.

3rd gear in the auto tranny is 16.5% lower than the 3rd gear in the manual tranny. You would need a 3.90 rear gear on the manual tranny to equal the 3.31 rear gear.

Where I lose it is in 4th gear, with my 3.31 rear gear. Both the auto and manual tranny are a 1:1 transmission ratio. And if the manual tranny has a 3.55/3.73/3.90/4.10 rear gear, it will accelerate faster....albeit with a successive lower top speed.

My rears are only 27.4" tall.

It's a bunch of tradeoff's. I have 390 rwhp and 370 rwtq with my small blower, so acceleration is ample for my needs.

you would know better numbers then i would with an auto .
my 5th gear was also an OD gear, and the 4.10 made it more of a racing gear now,

another reason your guys should be a manual and not an auto
manual makes the car\driver experience

 

[Pentalab]

you would know better numbers then i would with an auto .
my 5th gear was also an OD gear, and the 4.10 made it more of a racing gear now,

another reason your guys should be a manual and not an auto
manual makes the car\driver experience

You are correct. With a 4.10 rear gear, in 5th (OD) top speed would be 161 mph on the auto....vs 200 mph with the oem 3.31 rear gear on the auto.

With the 4.10 rear gear, all the rpms at any speed will increase by 1.239 (4.10 / 3.31) = 1.239

Back in 2011, when I bought the car 3rd hand, it was all that was readily available at the time. The idea was the wife could also use it if needed, hence the auto. Her car is the 2011 Fusion ( bought the Fusion, new back in 2011). Wife drove the mustang...once, that's it. Never drove it again.

 

[MrBhp]

You guys are talking about top speed differences with different gears. What rpm are you using as a limiter? My car is just as fast with the 4.10 as it was with the 3.55. No way a n/a 4.6 is going to run redline in 5th. And I get there a lot quicker.

 

[Pentalab]

You guys are talking about top speed differences with different gears. What rpm are you using as a limiter? My car is just as fast with the 4.10 as it was with the 3.55. No way a n/a 4.6 is going to run redline in 5th. And I get there a lot quicker.

I used 6k rpm for all my calcs. You are correct though, the car won't do 200 mph at 6k rpm in OD with a 3.31 rear gear....even with my small Roush blower. The wind resistance would kill it.

 

[Dino Dino Bambino]

Hello there, i'm wanting to change my gear ratio for my 2007 ford mustang 4.6 3v Auto but i don't know which one i want and would be best for my car so thought id ask for peoples experience and stats on what they got out of them as i can't seem to find the answers i'm looking for.

First of all my car is all NA and these are the modification's on it currently

Cold Air Intake Kit
Ford Performance Fuel Injector Set 24Lb EV6
Walbro High Performance Fuel Pump Kit 400 LPH
MSD Ignition Coil Packs
Runners Delete
Straight Piped and Decat

This car is my daily and so i'm not bothered for fuel economy, gas milage etc, my goal really is to go from 0 to 120mph as fast as i can but if i can make it go from 0 to 140mph or 150mph or more is a bonus as i don't want to sacrifice too much of my top end, i want the car to overtake cars alot more faster and easier if i need to overtake and also want to set off faster as well, especially on a roll. I used to drive really hard till i blew up my last engine and i been alot more tame but i still like to give it some shit when i want to, i drive way more sensible now compared. also my gearbox is fully been rebuilt as well so practically new inside.

I want to know everyone else's opinion on what would be best for me, the stats on what top speed you got on 3.73 and 4.10 gears roughly, rough times etc, or if you got videos i can watch would help a ton as well as it gives me an idea visually what to expect, some people say 3.73 barely does anything different and makes the gearbox shifting harder n stiffer, some say 4.10 is best for auto because it makes the biggest difference but gear changes can be overwhelming for the gear box and late shifts etc, some say you need a tune for the gear ratios some say not, i have no clue how true all this is but i want the best i can get out of my car,

Many Thanks

I think the 05-10 GT Automatic is a classic case where there's no need to fear the gear if it's N/A, whether it's bone stock or is lightly modded as in your case. The way to go is 4.10 axle gears and upgrade to a 3000rpm stall torque converter. The effect will be nothing short of dramatic compared to the stock converter and 3.31 axle gears.
Once you've done those, you'll be spinning the rear wheels a lot more easily and you'll need traction upgrades. You'll also be spinning the stock driveshaft over 20% faster so plan on upgrading to an aluminium unit.

 

[Midlife Crises]

I agree the 4.10 final gear is an excellent choice for auto or manual transmissions. Drivability is outstanding in the normal rpm range. The theoretical top speed doesn’t mean much until you have the power to pull it. I have been over 140mph with 4.30 gears and a T56 mag. I was not in top gear and was not red lined. Still accelerating strongly but the pucker factor said enough.

 

[whitmanink]

I agree the 4.10 final gear is an excellent choice for auto or manual transmissions. Drivability is outstanding in the normal rpm range. The theoretical top speed doesn’t mean much until you have the power to pull it. I have been over 140mph with 4.30 gears and a T56 mag. I was not in top gear and was not red lined. Still accelerating strongly but the pucker factor said enough.

i couldnt agree more with you and dino,
4.10 get this stigma,
where you will get 5 mpg, and you will be reving at 6000rpm @50mph on the highway ,
and lets not forget ,your top speed is reduced (as if we will ever see that)
ect ect..

unless you are over 475ish hp ,, id say 4.10 are the way to go,,
anything above and id say gear change is recommended for best use of the blower\turbo

 

[Dino Dino Bambino]

i couldn't agree more with you and dino,
4.10 get this stigma

That said the 4.10 isn't "one size fits all". I certainly wouldn't recommend it for a forced induction set up with a positive displacement supercharger or even a turbo. For a centrifugal it's fine because it builds boost gradually as the rpm increase, and peak torque is invariably above 5000rpm.
For N/A with a manual transmission and stock cams, 3.55 is ideal. Once you start adding cams, intake manifold, or ported heads that shift the torque curve higher up the rpm range, anything from 3.73 to 4.56 may work best depending on set up.

 

[Beerus]

I was leaning towards the 3.73 gears so i could have abit of top end but getting torn now towards 4.10 due to it being better for the 5r55s trans

 

[Dino Dino Bambino]

I was leaning towards the 3.73 gears so i could have abit of top end but getting torn now towards 4.10 due to it being better for the 5r55s trans

The 4.10 would give you a higher top speed in 5th gear since it would bring it much closer to the rpm where the engine makes peak HP.

 

[Beerus]

The 4.10 would give you a higher top speed in 5th gear since it would bring it much closer to the rpm where the engine makes peak HP.

It depends how on what top speed i get tho, i want to be hitting minimum 150 maximum 160mph