3.15 vs 3.55 axles

[MUSThavaSTANG]

So I plan to order a V6 with the axle upgraded to the 3.55. As I understand it this will give me better acceleration in the lower rpms than the 3.15, but lower top speed and mpg. Seems like a fair trade to me.

What I'd like to know is just how different the 3.55 feels from the 3.15. How noticeable is the improved acceleration? Thanks.

Sponsored

 

[aspensilver]

It's noticeable in low gears/from a stop. Less noticeable on the highway.

 

[venom_e92x]

Glad they did away with the 2.73 axle ratio altogether.

 

[ort895]

thinking i might go with the 3.55s as well but i do wonder what difference it actually makes.

 

[gojensen]

That 3.55 is about the only thing pulling me to the EB pp ... But I have no idea what difference it will make in an auto hoping for faster acceleration from 0-35 I guess

 

[deeps29]

Even I'm confused about this thing. I am looking at EB with auto transmission. I have to decide between 3.15 or 3.55 (without or with PP). Hoping for people to shed more light on this topic.

 

[FiveLiterDreamer]

is the difference similar on a 5.0?

 

[Chambo007]

is the difference similar on a 5.0?

I'd like to know this too. I plan on doing some casual drag racing for kicks with the guys once a month or so. Should I stick with the 3.15s for the "longer legs" or go with the optional 3.55 for faster acceleration but maybe too many shifts? Which would be better with a tune or suspension upgrades?

 

[Trackaholic]

Just made a spreadsheet to compare the various final drive choices, but it gets complicated pretty quick with all the tire options (which also have various diameters and therefore effective gear ratios).

But, it looks like the GT PP with have the following shift points @ 6900 RPM (not sure what the actual redline is):
1-2 = 41.6 MPH
2-3 = 62.6 MPH
3-4 = 90.2 MPH
4-5 = 116 MPH
5-6 = 152 MPH
6th gear @ 60 MPH = 1770 RPM

I would expect the car to be hitting redline in 4th at the end of the 1/4 if my numbers are correct, so gearing is probably just about right for stock (maybe a little bit short).

GT with 3.55 and 20" wheels (265/35-20):
1-2 = 43.2 MPH
2-3 = 64.9 MPH
3-4 = 93.6 MPH
4-5 = 120 MPH
5-6 = 157 MPH
6th gear @ 60 MPH = 1710 RPM

This one might be a bit better, if you think the trap speeds could get up to 120. C7 seems to be running about 117-120, so I think the Mustang would need some mild mods to get there (not familiar with what the Mustangs run). This might be good for a car with mild mods.

Finally, the GT with 3.31 and 20" wheels:
1-2 = 46.1 MPH
2-3 = 69.5 MPH
3-4 = 99.9 MPH
4-5 = 128 MPH
5-6 = 168 MPH
6th gear @ 60 MPH = 1600 RPM

With the 3.31 gears you'll still need to shift to 4th, but you'll be lower in the power band. Would be good for a modded car with much greater power.

Of course, you always have the option of shifting to 5th.

-T

Edit: Corrected the last chart. Was using 3.15 gears that aren't available with a manual. Changed to the 3.31 gears and updated speeds accordingly.

 

[Grimace427]

Finally, the GT with 3.15 and 20" wheels:
1-2 = 48.6 MPH
2-3 = 73.2 MPH
3-4 = 105 MPH
4-5 = 135 MPH
5-6 = 177 MPH
6th gear @ 60 MPH = 1530 RPM

Your first two ratio sets were good, but this one is off because you forgot the 3.15 rear gear ratio only comes with the automatic trans. You probably meant to use 3.31 rear gears.


Auto gear ratios:

1. 4.17
2. 2.34
3. 1.52
4. 1.14
5. 0.87
6. 0.69

3.15 gears with auto trans and 20" tires:

1. 43mph
2. 77mph
3. 119mph
4. 158mph
5. 207mph
6. HAHAmph

RPM's in 6th @ 60mph: 1600


edit: this is also assuming 7,000rpm redline.

 

[Grimace427]

3.31 gears with manual transmission and 20" tires:

1. 47mph
2. 71mph
3. 102mph
4. 130mph
5. 172mph
6. FUNNYmph

RPM's in 6th @ 60mph: 1600




I also built a list of various RPM's and trap speeds for the 1/4 mile with different gear ratios and tire sizes. If you are racing at the drag strip you have to consider the proper drag tires, and those are commonly either 26" or 28" tall. So with that I calculated RPM shift points and trap speeds considering vehicle power from mods, gear ratios, tire sizes, and accross the various models(V6, V8, Shelby, Tremec swaps). I put in as many variables as I could.

http://www.fastfordmuscle.com/index.php/topic/192-gears-gears-gears/?hl=gears

 

[Trackaholic]

Your first two ratio sets were good, but this one is off because you forgot the 3.15 rear gear ratio only comes with the automatic trans. You probably meant to use 3.31 rear gears.

Thanks for the correction. I originally mis-typed 3.13 instead of 3.31, but when I went to fix it I saw the 3.15 for the automatic and accidentally put that in.

I'll have to update the spreadsheet when I get home.

-T

 

[deven2015GT]

3.31 gears with manual transmission and 20" tires:

1. 47mph
2. 71mph
3. 102mph
4. 130mph
5. 172mph
6. FUNNYmph

RPM's in 6th @ 60mph: 1600




I also built a list of various RPM's and trap speeds for the 1/4 mile with different gear ratios and tire sizes. If you are racing at the drag strip you have to consider the proper drag tires, and those are commonly either 26" or 28" tall. So with that I calculated RPM shift points and trap speeds considering vehicle power from mods, gear ratios, tire sizes, and accross the various models(V6, V8, Shelby, Tremec swaps). I put in as many variables as I could.

http://www.fastfordmuscle.com/index.php/topic/192-gears-gears-gears/?hl=gears

Can either you or the OP tell me what the 3.55 would be with the 20" tires on the GT? That's what I've ordered and I figure 0-60 time will be improved a little with the 3.55:1 gear ratio over the 3.31:1 ratio.
How will each gear look? (assuming redline is 7000rpm, but will more than likely be 6500rpm I'm guessing)

 

[Grimace427]

Can either you or the OP tell me what the 3.55 would be with the 20" tires on the GT? That's what I've ordered and I figure 0-60 time will be improved a little with the 3.55:1 gear ratio over the 3.31:1 ratio.
How will each gear look? (assuming redline is 7000rpm, but will more than likely be 6500rpm I'm guessing)

Manual or auto trans?


Assuming manual transmission, 265/35/20 tires, 3.55 gear ratio, and 7,000rpm redline:

1. 44
2. 66
3. 95
4. 121
5. 160
6. koenigsegg

RPM's in 6th @60mph: 1,700rpm

http://www.f-body.org/gears/

 

[Grimace427]

Trackaholic actually got it in his first post.

Sponsored