What final (rear end) gear ratio should I go with?

jusinbailey · Dec 19, 2003

I have probably started to annoy you guys with my newbie questions, but I really need to figure this out

I have decided to go with the t5 tranny and need to decide on the rear end. This is a daily driven car and it wil see the hwy quite often. I want something that is easy on the hwy but packs enough unf for the faster street cars.

Well, we have a 3.73 rearend sitting in the garage ready to be used. Its either going in my 65 stang or my fathers cobra. Havent completely decided if I want to use that or start a search for a different ratio.

Does it matter much if one finishes the 1/4 mile in 3rd or 4th gear? I have heard people say that they prefer to finish in 3rd gear. any reason to this? also, from an earlier post someone mentioned that 10:1 is the ideal 1st gear final ratio.

gear ratio of the t5 year i will be searching for:
3.35 1.99 1.33 1.0 .68

If i use 3.55's I will get the following result @6000 RPM:
1st: 40mph (final of 11.89)
2nd: 67mph
3rd: 101mph
with this setup it will allow me to cruise at 70mph/2120rpm

If i use 3.73's I will get the following result @6000 RPM:
1st: 38.3mph (final of 12.5)
2nd: 64.4mph
3rd: 96.4mph
with this setup it will allow me to cruise at 70mph/2227RPM

as you can see, the 3.73 will require me to finish in 4th gear

are these differences too minimal for me to be worrying about it?

EDIT: tires are 245x45x17 (26 inches diameter) and the motor is a 302/347 at ~400HP (flywheel)

dodgestang · Dec 19, 2003

jusinbailey said:
I have probably started to annoy you guys with my newbie questions, but I really need to figure this out I have decided to go with the t5 tranny and need to decide on the rear end. This is a daily driven car and it wil see the hwy quite often. I want something that is easy on the hwy but packs enough unf for the faster street cars.

Well, we have a 3.73 rearend sitting in the garage ready to be used. Its either going in my 65 stang or my fathers corvette. Havent completely decided if I want to use that or start a search for a different ratio.

Does it matter much if one finishes the 1/4 mile in 3rd or 4th gear? I have heard people say that they prefer to finish in 3rd gear. any reason to this? also, from an earlier post someone mentioned that 10:1 is the ideal 1st gear final ratio.

gear ratio of the t5 year i will be searching for:
3.35 1.99 1.33 1.0 .68

If i use 3.55's I will get the following result @6000 RPM:
1st: 40mph (final of 11.89)
2nd: 67mph
3rd: 101mph
with this setup it will allow me to cruise at 70mph/2120rpm

If i use 3.73's I will get the following result @6000 RPM:
1st: 38.3mph (final of 12.5)
2nd: 64.4mph
3rd: 96.4mph
with this setup it will allow me to cruise at 70mph/2227RPM

as you can see, the 3.73 will require me to finish in 4th gear

are these differences too minimal for me to be worrying about it?

Selecting the proper gear ratio has a lot to with what size tries you will run and perhaps most important....what is the motor set up with? You want gears that will keep you right in peak power band of the motor.

jusinbailey · Dec 19, 2003

dodgestang said:
Selecting the proper gear ratio has a lot to with what size tries you will run and perhaps most important....what is the motor set up with? You want gears that will keep you right in peak power band of the motor.

i updated the specs into the original post. thanks

restomod · Dec 19, 2003

all the 5.0 guys i know that have t5s use 3.73 gears in their cars.they say that is the best gear for t5s. i on the other hand will stay with my c4 for a while. i run 3.40 gears in both my stangs . it seems to be a good combo.

RGS0907 · Dec 19, 2003

If you already have the 3.73 sitting at home, I would go with that. The difference between that and a 3.55 is not that much, and besides you'll get a little more punch in the lower gears & still have the 5th gear which will make your final drive 2.53:1 which is great for the highway. If anything, you could even bump it to 3.91 or better which puts your final drive at 2.65.

dodgestang · Dec 19, 2003

jusinbailey said:
i updated the specs into the original post. thanks

What intake, what cam, what carb?

What I am getting at is this...is the motor built to make power from 0-4k or from 2k to 6k etc....each combo will have it own individual HO and torque curve...the 3.73 sound like a good choice but without knowing the RPM range the motor was built for and an idea where the peak torque is its a shot in the dark....with the 3.73 you may find yourself out of the motor's power band too fast for first gear to be of any value to you and then the drop to second.....anyway just something to consider....when selecting your gear.....a lot of people sometimes over gear their car.

I run 4.11 in my stroker power 65, but my power band doesn't start till I'm about at the 3k so I need something that will get me up in the RPMs very fast and keep me there. I also added the 2.85 first gear in my modyfied AOD for that much more start up....but it would be way too much gearing if I had a warned up 289 and I would be out of my power range way to fast.

SadbutTrue · Dec 19, 2003

With a T5 usually 3.73 - 4.11 are best. People use the 3.50s when they have C4 and other non overdrive trannies.

jusinbailey · Dec 19, 2003

dodgestang said:
What intake, what cam, what carb?

What I am getting at is this...is the motor built to make power from 0-4k or from 2k to 6k etc....each combo will have it own individual HO and torque curve...the 3.73 sound like a good choice but without knowing the RPM range the motor was built for and an idea where the peak torque is its a shot in the dark....with the 3.73 you may find yourself out of the motor's power band too fast for first gear to be of any value to you and then the drop to second.....anyway just something to consider....when selecting your gear.....a lot of people sometimes over gear their car.

I run 4.11 in my stroker power 65, but my power band doesn't start till I'm about at the 3k so I need something that will get me up in the RPMs very fast and keep me there. I also added the 2.85 first gear in my modyfied AOD for that much more start up....but it would be way too much gearing if I had a warned up 289 and I would be out of my power range way to fast.

everything edelbrock performer RPM, heads, cam, intake, edelbrock 750 carb.
i was considering an 800 carb and a comp cam designed for 2500-6500rpm. not sure if it would be worth it or not.

67GTA-FB429 · Dec 19, 2003

Ideally you want to be at the top of your power curve as you cross the 1/4 line, in your top gear (not counting overdrive). If you are in 3rd and still had fourth, you have left something on the table. The best way to find out is by taking it to the track once, getting a few runs in and then you can easily calculate which way you need to go in gearing.

6Stang7 · Dec 19, 2003

I orderd my 4.11's two days ago.

I can't wait to get them in!!!!!

-Shaun

gp001 · Dec 19, 2003

What rear gear set fits a 65 stang or a corvette?

302 coupe · Dec 19, 2003

that's what I was wondering.....

302 coupe · Dec 19, 2003

restomod said:
all the 5.0 guys i know that have t5s use 3.73 gears in their cars.they say that is the best gear for t5s. i on the other hand will stay with my c4 for a while. i run 3.40 gears in both my stangs . it seems to be a good combo.

I've never heard of a 3.40 gear in a ford, so I doubt they exist at least for 8/8.8/9 inch rears. They jump from 3.25 to 3.50.

jusinbailey · Dec 19, 2003

gp001 said:
What rear gear set fits a 65 stang or a corvette?

i didnt know what you meant by this post until i read my original post again. silly me. cobra. why i said corvette i have no clue.

restomod · Dec 19, 2003

well 302coupe, i do have a 3.40 and it is out of a pinto 8" rear.wether you have heard of one or not they do exist.by the way i have two of them!!!!!!! :jaw:

p.s. you need to check out www.ultrastang.com you will find the info in the 9" section. they show a 3.40,3.45,3.50 and a few others.have a nice day. :rolleyes:

302 coupe · Dec 20, 2003

restomod said:
well 302coupe, i do have a 3.40 and it is out of a pinto 8" rear.wether you have heard of one or not they do exist.by the way i have two of them!!!!!!!

p.s. you need to check out www.ultrastang.com you will find the info in the 9" section. they show a 3.40,3.45,3.50 and a few others.have a nice day.

interesting....I've been to ultra's site more than my fair share of times so don't worry about that. Congrats on having 3.40's, double congrats on having 2. Heres to you :cheers:

12sec67 · Dec 20, 2003

go with thw 3.73's

i run 4.11's in mine and cruise 70 approx 2600 with an AOD

Edbert · Dec 20, 2003

12sec67 said:
go with thw 3.73's

i run 4.11's in mine and cruise 70 approx 2600 with an AOD

That sounds high to me, what is your tire diameter?

12sec67 · Dec 20, 2003

Edbert said:
That sounds high to me, what is your tire diameter?

275/50/15 25.5" tire

67GTA-FB429 · Dec 21, 2003

I wish I could run 2600rpm at 70 mph...with my 429 and 3.50s I run 3500 at 70. But then again I have a quater mile C6 with only 3speeds.

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