Keep searching and you will find a million posts pertaining to gears. Most people will say 3.73's for manual and 4.10's for auto. I say 4.10's regardless, but thats my opinion. Whatever you decide to go with, it will give you better acceleration and get you into your powerband quicker. However, it will increase your rpm's, which is a concern for people who do alot of highway driving. I would not worry about top speed, as you should still top out at over 140 mph in 5th.

With 4.10s....

With stock size tires you can go 150 mph at 5393 rpm in 5th gear. Check out the rpm calculator in the tech section.

As posted above, you will loose some top end but not much. I think it's well worth it. Your 0-60 time will improve greatly as well as your 1/4 mile time. If you don't mind spending some money on gas go with the 4.10's. If you drive a lot of highway miles stick with the 3.73's so you save the gas. If you plan on supercharging/turbo'ing your car in the future stick with the 3.73's (maybe even stock). Good luck...

I can tell you that with my 3.90's, 4th gear tops out at 115...

Kyle,

It does NOT affect top speed, not in a negative way; see the calculation:

80 mph @ 2400 RPM (stock 3.27 gears stock tire dimension)
at a top speed of 137 mph this would be 4110 RPM again with the stock gears. (That's what Ford prooved)

Lets see what the 4.10 gears do:
80 mph @ 3009 RPM (4.10 gears, stock tire dimension)
at the same top speed of 137 mph this would be 5153 RPM

Since we know speeds and RPM's lets have a look at a stock RPM / HP graph of a 4.6 L
At 4110 Rpm's (with 3.27 gears) you see aproximately 195 RWHP that can be used to move the car against air drag. And at 137 mph the car stops acelerating because the force from the air drag equals the force from the motor applied at the wheels.

Now with the 4.10 gears we are looking at roughly 5153 RPMs and a stock Mustang has about 210 RWHP at this RPM.
What does that tell us now? If your car has more HP at a certain speed and with a certain RPM, your car is able to apply more force to the ground.
Thererfore the force of drag can even be higher which would mean at even higher speeds.

WITH 4.10 instead of 3.27 and in 5th gear, with stock tire size (245/45 17) your car WILL go faster! How much? I cant tell. thats a whole different ball game (lots of math, and it requires an acurate dyno chart)

Kyle82484 said:

I have an '03 Mustang GT and I am considering getting some 4.10 gears, I have been reading some other threads regarding gears, but I am wondering what specifically will a set of gears do for the performance of my car, such as a set of 4.10 gears? I saw someone posted that it affects the overall top speed of the car? If so how much? Are 4.10 gears the best ratio for my car?

Click to expand...

I just don't trust those calculators! According to the one on this site, I should be running at about 3000 RPMs at 80 MPH, but I'm not. Now I have read that 03+ GT's have a .62:1 5th gear ratio as opposed to a .68:1. If this is true, the calculator estimates 2650 RPMs at 80, which is exactly what I run :shrug .

I agree with engineer76, before my 3.73s I had a hard time getting to 135, after the gears I did 147 and it was still going, I ran out of room. The car was in its power band thats why it went faster. If I had enough horse power to redline in 5th I would be going 183 mph. With 4.10s 166 mph... The thing is mostly stock 4.6s fall off at 5500 or below so any extra rpm is useless. I think had I had more room that day I could have gone 155-160.

Id just like to add something to consider, I have no calculater or anything of that nature but I have to agree with what some one said about not putting too much faith in those calculaters.

It may not be by a huge amount but it makes more sense to me that you would lose some top end with higher ratio gears because at some point your going to reach a point of no return, the motor is just not going to be able to spin fast enough. (the higher the gear the more the motor has to spin it to make power.)

Here's my unscientific example, Ive seen several Supra vs Mustang's, both at about the same hp but in the end, in a top end run the Mustang generally falls behind. It seems that the Mustangs higher gears allow it to make the Jump on the Supra but the Supra with its low high way gears seems to just pull away in the end cause the Mustang has given all its got early in the fight. On a 1/4 run thats ok, but on an open run its just not an advantage.

Just my unscientific observation.

Good observation Stonecold! Does a Supra have a 6-speed? If so, that could very well be the advantage.

One question you should ask yourself Kyle, what are your plans with your setup? Are you setting up for the 1/8th? 1/4? road racing? street racing? running from the cops...J/K of course. My setup if mainly for the 1/8th, with and occasional 1/4 when I feel like making the long trip to MD, and of course the occasional street race. One thing I will not be doing is racing 150 MPH down the highway, my one race up to 110 was more than fast enough and I punished myself for doing even that. What ever you decide to do, have fun and keep it safe!

The Supra does indeed have a 6 speed Funky.

FunkyBoss said:

Good observation Stonecold! Does a Supra have a 6-speed? If so, that could very well be the advantage.

One question you should ask yourself Kyle, what are your plans with your setup? Are you setting up for the 1/8th? 1/4? road racing? street racing? running from the cops...J/K of course. My setup if mainly for the 1/8th, with and occasional 1/4 when I feel like making the long trip to MD, and of course the occasional street race. One thing I will not be doing is racing 150 MPH down the highway, my one race up to 110 was more than fast enough and I punished myself for doing even that. What ever you decide to do, have fun and keep it safe!

Click to expand...

I like mine because like above... I don't expect to be driving that fast normally.. and most races are over by the time you're goin that fast anyways.. I can take 4th gear to 110-115, that's my limit... no point in going faster - just easier for someone to get hurt

Guys, believe dollarbill or me - it's just a fact.

MATH DOESN'T LIE!

What year is your car.... because those gearing are pre set for a T 45, the 1st gear and 5th gear ratio are just a tad bit different with the TR3650 in the 02+ cars

1st = 3.37
5th = .67 (little bit better O/D)

FunkyBoss said:

I just don't trust those calculators! According to the one on this site, I should be running at about 3000 RPMs at 80 MPH, but I'm not. Now I have read that 03+ GT's have a .62:1 5th gear ratio as opposed to a .68:1. If this is true, the calculator estimates 2650 RPMs at 80, which is exactly what I run :shrug .

Click to expand...

My T-45 has 3.37 and .67 also, I always change them when I use the calculator....http://www.allfordmustangs.com/Detailed/608.shtml

carguy1985 said:

What year is your car.... because those gearing are pre set for a T 45, the 1st gear and 5th gear ratio are just a tad bit different with the TR3650 in the 02+ cars

1st = 3.37
5th = .67 (little bit better O/D)

Click to expand...

If the TR3650 has a numerically lower OD (i don't doubt that) the effects on top speed, making the car go faster, will even be more noticable with 4.10 gears.

Just imagine something:
If the car maxes out at 135 mph (top speed) what happens at this point?
X Horsepower (from the motor at a given RPM) are fighting with the drag of air. And at top speed they are both equally strong - Force wise we have an equilibrium.
By the way: at this time your car only puts about 190 Horses to the ground.
(because the motor only revs at 4100 RPM)

Wouldn't it be nice to be able putting down all the 225 possible horses to the ground, cause this would make the car go faster? (5500 RPM)
And that's exactly when the change of gears "gives" you the extra top speed.
Your motor is able to rev higher at the same speed, and therefore puts down more HP to the ground. If you have more horses to fight wind drag, you are not in an equilibrium yet. Your car will increase speed until the 225 HP (vs. only 190) now are in an equilibrium with air drag.
YOUR CAR WILL GO FASTER!
THE EFFECT OF 410 EARS WILL EVEN BE MORE NOTICEABLE WITH THE LONGER OD TR3650.

By the way: there is no easier way to explain it

oh i understand, it will make a difference lol

my buddies car has a t45 and his cars at 2 grand in 5th with his 373s at 60mph
my car is tr3650 and is at 2 grand in 5th gear with 373s is almost 65mph.

http://www.ttcautomotive.com/English/products/TR-3650.asp This is the Tremec website, it shows several different ratios available for the 3650. Which one does the stang have? This will be benficial to properly use the calculator. I know my T-45 has only one set of ratios.

I have a 03 GT and installed 4:10 gears. I never been happier. I never had the car at the track, but I did wind it up a number of times but never really WOT and it was like a bat out of hell through the gears. Hard at times in wet weather (I could start off in second), but other then that it is great.