whats a good rear pinion gear ratio for a 03 mustang GT?

[afarrell39116]

I have been debating this for a while and thought i would try to reach out to others for more opinions. Im wanting to try to find that perfect rear wheel gear ratio. Yes i know different ratios are ment for certain purposes as to what you want to be doing. I want to get a good start off in 1st gear and be up at a decent speed before getting into 2nd...was thinking around 20-25mph. Ive considered going with 4:10's but still unsure. Any feedback would be greatly appreciated. Thanks!!

[devildog214]

if its a 5sp 4.10s wouldnt be too bad, for a auto no more than 3.73

[jpalamar]

Depends on your mods and driving plans.

[afarrell39116]

Yeah ive seen alot of vids and alot of them had their mods listed, with alot of 4:10.s listed for the rear. When i get going from a stop in 1st gear i dnt want to be at like 4k rpm's and.be doing 15 mph lol i just want to have a lil more get up and go. I wish i knew what was in it now, but idk.

[afarrell39116]

And yes its a 5 speed lol

[schaffer]

You should be able to find out what's in the rear on the axle tag. My ranger has one on the axle,printed on it was 3.73.

[afarrell39116]

This is true i didnt think of that lol but what if the owner before me has already changed them out? How can i tell what ratio the rear gears are?

[OutToWinPAHC]

Count the teeth on the input pinion and out put pinion then divide the output by the input example 12 and 47 would be 3.916

[afarrell39116]

Oh ok yeah i thought it would have to do with counting the teeth...i just didnt know what the formula was. Thanks!

[schaffer]

I'd check the axle tag first,maybe contact the previous owner.

[mayer5oh]

Spin the wheel at the end around one exact rotation and count how many times the pinion turns around. That's a good way to figure out the gears in the car. As for a stock-ish 4.6 the 410s would be great. What are your present and future mods?

[Dilley]

If you plan on ever going forced induction don't do the 4.10s

[dnasty2g]

Yeah ive seen alot of vids and alot of them had their mods listed, with alot of 4:10.s listed for the rear. When i get going from a stop in 1st gear i dnt want to be at like 4k rpm's and.be doing 15 mph lol i just want to have a lil more get up and go. I wish i knew what was in it now, but idk.

4.10s would be making first shorter then stock..

[dugganzx3]

There's calculators out there to figure out what rpm/mph you'll be spinning in each gear with different ratios. I know my car with the 3.8L and the t-5 5 speed, will be around 2200-2400 rpm around 62 mph with 4:10's. Right now with 3:42's i can do 62 around 1950-2100 rpm. Our car's are apples and oranges, but you should be close to the same RPM's I'd imagine. So that means doing 75 mph for a long trip on the highway will be a nightmare, if you daily drive this car on the highway, you may want the 3:73's or even 3:90's.

[afarrell39116]

well as of now im still planning and deciding future projects for the GT. Moneys tight and everyone i know understands that lol. Im hoping one day to get it supercharged but i know that wont be for a loooonnng time due to how expensive they are. Im planning soon though to get rid of the bassani exhaust system thats on it currently and putting on flowmasters, the bassani just isnt loud enough for me lol. And yes i believe we're around the same RPM ranges. This is my daily driver and it does see a little bit of highway time every day to work and back. I can cruise pretty steady at about 70 mph and be at or around 2500 i believe is what i seen last.

[HickRocket1258]

If it won't be for a long time just do 4.10s. You'll run out of 1st gear in no time but who cares. Make sure you don't just change the ring and pinion out, but also get the bearing rebuild kit. 3.73s will be going in my auto once my Vortech is tuned.

[jpalamar]

well as of now im still planning and deciding future projects for the GT. Moneys tight and everyone i know understands that lol. Im hoping one day to get it supercharged but i know that wont be for a loooonnng time due to how expensive they are. Im planning soon though to get rid of the bassani exhaust system thats on it currently and putting on flowmasters, the bassani just isnt loud enough for me lol. And yes i believe we're around the same RPM ranges. This is my daily driver and it does see a little bit of highway time every day to work and back. I can cruise pretty steady at about 70 mph and be at or around 2500 i believe is what i seen last.

Bassani > Flowmaster.

You want louder get long tubes.

[HickRocket1258]

I was planning on doing a lot with my 2002. Wanted to keep it N/A, but realized, I want to have some fun. Superchargers you can find cheaper used and that's the route I went.

I have SLP Loudmouth II and love it. Good for cruising and has some rumble, and then when you get on it, it's loud.

[afarrell39116]

Well actually i stand corrected lol it has a bassani x pipe with earlier style magnaflow mufflers. So id like to run flowmasters from the x back and yes im considering long tubes...just dont know which to go for

[bmatyeah]

For gears I would stay away from 4.10 if you drive at 65+ and drive a lot. It will put you higher up in the rpms, not horrible but who wants to put more money in the gas tank? For a dd, I would put in 3.73 or possibly 3.90.

Get long tubes, if you want a louder exhaust the bassani is better quality then the flowmasters.

SLP long tubes sound awesome. Remember you get what you pay for with headers.

[afarrell39116]

Yeah i was on american muscle and seen their charts they have for each gear set..3.73.s are lookin good at this point so far lol

[HickRocket1258]

4.10s man. You are maybe losing 2 mpg if that.

Only get the long tubes if you are planning on doing them yourself, otherwise you might get shops that reject doing them for you or they will charge a silly amount of the install. It's not an easy one at all.

[afarrell39116]

Yeah ill do them myself at my work on a day off..i try to do most of my own work the best i can.

[Chris B.]

This is true i didnt think of that lol but what if the owner before me has already changed them out? How can i tell what ratio the rear gears are?

You can figure it out by putting the car in 4th or 5th gear at a fixed speed and checking the RPM then calculating the gear ratio.

This page may help:
http://www.corral.net/tech/gearcalc.html

I currently have 4.10 gears and I absolutely hate them. 1st gear is completely useless and it feels like I'm driving a 4 speed most of the time. In daily driving I start out in 2nd gear almost all of the time. Also, the engine is turning 2700-3000 RPM on the highway. 4.10's seem to be good if you main purpose is 1/4 mile racing.

[afarrell39116]

Yeah quarter mile runs are not in my near future just yet lol

[HickRocket1258]

4.10s are needed in my opinion for the lousy 4.6 2v motors. Yes first gear isn't worth it really for 4.10s, but I still stand by them.

[AutobahnRacer]

This should be in the vehicle specific forum or drivetrain section.

[afarrell39116]

Yeah sorry...but hey it says for this forum "post ANY and ALL automotive chats/discussions here" so its not like i tried to start this chat in the "gallery" or "new to tst" forums.....just saying ;)

[Dilley]

I have bassani x and cat back and trust me it is plenty loud I'm not a fan of the lower end stuff (flowmaster magnaflow etc) due to the amount of horror stories

For your gear if you don't mind switching them out once you get the s/c then go 4.10s otherwise 3.73 or 3.55

[clubken]

I had 373s in my 2000 and always wished I did 410s

[afarrell39116]

Thanks for all the help guys i really appreciate it...but it just sucks because everyone is like yeah go 4.10s the its no no do 3.73s lol back and forth back and forth i will hopefully make a decision soon.

[clubken]

The decrease in fuel mileage will not be that noticeable and still 100% driveable. Go with 4.10s!

[1988 Olds]

I might as well chime in on this disscusion as well. I would have to say go with 3.73s since it's your daily driver and you said you drive on the hwy sometimes. Unlike you my dad drives his car maybe 2-3times/week 4-5 miles/day. My dad has a 2001 GT with Intake, Cat-Back, 4.10s and tune and it runs pretty good. If you like to take a ride sometime I'd be more then happy to take you for one. I'm in Levittown.

[russiankid]

Are you planning on doing the gears yourself? If yes, and you've never done gears before, start reading up on how to set back lash.

[HickRocket1258]

I installed a supercharger on my mustang, but I wouldn't trust myself with doing gears.

[jpalamar]

The average person is better off with 3.73s.

[HickRocket1258]

The average person is better off with 3.73s.

Until they get in one with 4.10s and realize they should have gone that route.

The only reason most people get concerned with losing mpg when driving is because they find themselves getting on it a lot more after the install.

[russiankid]

I installed a supercharger on my mustang, but I wouldn't trust myself with doing gears.

Installing gears is straight forward, only thing is it becomes tricky in the end when you set back lash. It has to be perfect otherwise you will chew the ring and pinion rather quickly. I am not sure if gear sets come with shims or not, but I would look into that and order shims if they don't come with it.

[Chris B.]

On a 2003 GT with the 0.675 5th gear ratio and stock size tires, here will be your engine RPM(rounded to the nearest 5 RPM) with the following gears.

4.10
65 MPH 2350 RPM
75 MPH 2715 RPM
85 MPH 3075 RPM

3.90
65 MPH 2240 RPM
75 MPH 2585 RPM
85 MPH 2930 RPM

3.73
65 MPH 2140 RPM
75 MPH 2470 RPM
85 MPH 2800 RPM

3.55
65 MPH 2040 RPM
75 MPH 2350 RPM
85 MPH 2665 RPM

3.27
65 MPH 1875 RPM
75 MPH 2165 RPM
85 MPH 2455 RPM

My 2008 GT had 3.55 gears and my 2005 GT has 4.10 gears and mild cams. The 2005 GT gets a consistent 4 to 6 MPG less on the highway than the 2008 GT did at the same speed over the same routes. That was with the same 18" wheels and 255/45-18 tires on both cars. Probably a large part of that is the additional ~400 RPM the 4.10 gear equipped car has to turn at the same highway speed.

If you can't decided between 3.27's and 4.10's, get 3.90's to split the difference.

[afarrell39116]

well i was out tonight and kept it steady at 45 mph and was a hair away from 1500 rpms....i whent back to the rpm chart from american muscle and apparently i have 3.90 gears lol the chart showed 45 mph at 1472 rpm's.

[afarrell39116]

i clarify....i was at 45 mph and 1500 rpm's in 5th gear