3.15 vs 3.55?

[Jetnoise]

Someone has way to much free time.....none of it means doodle vs seat of the pants

With the single OD MT82:

3.15
After 1st Shift: 4,980 RPM. 33.61 % RPM Drop
After 2nd Shift: 5,216 RPM. 30.45 % RPM Drop
After 3rd Shift: 5,858 RPM. 21.89 % RPM Drop
After 4th Shift: 5,682 RPM. 24.24 % RPM Drop
After 5th Shift: 4,875 RPM. 35.00 % RPM Drop

1st Gear is 52.86 MPH at 7500 RPM
2nd Gear is 79.61 MPH at 7500 RPM
3rd Gear is 114.47 MPH at 7500 RPM
4th Gear is 146.56 MPH at 7500 RPM
5th Gear is 193.45 MPH at 7500 RPM
6th Gear is 297.62 MPH at 7500 RPM1

3.31
After 1st Shift: 4,980 RPM. 33.61 % RPM Drop
After 2nd Shift: 5,216 RPM. 30.45 % RPM Drop
After 3rd Shift: 5,858 RPM. 21.89 % RPM Drop
After 4th Shift: 5,682 RPM. 24.24 % RPM Drop
After 5th Shift: 4,875 RPM. 35.00 % RPM Drop

1st Gear is 50.30 MPH at 7500 RPM
2nd Gear is 75.76 MPH at 7500 RPM
3rd Gear is 108.94 MPH at 7500 RPM
4th Gear is 139.47 MPH at 7500 RPM
5th Gear is 184.10 MPH at 7500 RPM
6th Gear is 283.23 MPH at 7500 RPM

3.55
After 1st Shift: 4,980 RPM. 33.61 % RPM Drop
After 2nd Shift: 5,216 RPM. 30.45 % RPM Drop
After 3rd Shift: 5,858 RPM. 21.89 % RPM Drop
After 4th Shift: 5,682 RPM. 24.24 % RPM Drop
After 5th Shift: 4,875 RPM. 35.00 % RPM Drop

1st Gear is 46.90 MPH at 7500 RPM
2nd Gear is 70.64 MPH at 7500 RPM
3rd Gear is 101.57 MPH at 7500 RPM
4th Gear is 130.04 MPH at 7500 RPM
5th Gear is 171.66 MPH at 7500 RPM
6th Gear is 264.09 MPH at 7500 RPM

3.73
After 1st Shift: 4,980 RPM. 33.61 % RPM Drop
After 2nd Shift: 5,216 RPM. 30.45 % RPM Drop
After 3rd Shift: 5,858 RPM. 21.89 % RPM Drop
After 4th Shift: 5,682 RPM. 24.24 % RPM Drop
After 5th Shift: 4,875 RPM. 35.00 % RPM Drop

1st Gear is 44.64 MPH at 7500 RPM
2nd Gear is 67.23 MPH at 7500 RPM
3rd Gear is 96.67 MPH at 7500 RPM
4th Gear is 123.77 MPH at 7500 RPM
5th Gear is 163.37 MPH at 7500 RPM
6th Gear is 251.34 MPH at 7500 RPM

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[WildHorse]

Someone has way to much free time.....none of it means doodle vs seat of the pants

Yeah who needs mathematics eh.. It's more the OP to give him a general idea. Thanks.

 

[Jetnoise]

Not questioning your math skilz.....
Now tell me what the rpm is at 70mph in top gear

 

[WildHorse]

Not questioning your math skilz.....
Now tell me what the rpm is at 70mph in top gear

3.15 = 1764rpm
3.31 = 1854rpm
3.55 = 1988rpm
3.73 = 2089rpm

Assuming 27.3" tall tire. :cheers:

 

[drabon74]

I have the 3.15, run my car through the track app and get 4.5 0-60 and it is spinning like crazy all the way to 60 with a 2.0-2.1 60 ft. This is with the stock pirelli all season 255-50-19. On a regular street asphalt, not a drag strip. The 3.55 May be faster but the 3.15 are by no means sluggish or slow. My Lund tuned 15 with headers never got better than 4.6 with much better tires(285-35-20 mpss)

 

[Hack]

:amen:
“At 20 mph the advantage of the 3.55s is gone. The advantage of the 3.55s is at launch (this means 0 MPH). In other words, your tests aren't set up correctly to find the answer to the question.”
Bull Crap!

Good come back! :lol:

 

[VooDooDaddy]

3.15 = 1764rpm
3.31 = 1854rpm
3.55 = 1988rpm
3.73 = 2089rpm

Assuming 27.3" tall tire. :cheers:

I just checked my last set of data-logs I sent off to LUND.

With a 3.15 rear diff. ratio, and 305/35-19 rear tires, my car (w/auto trans) is turning 1950 rpm @ 70mph.

I thought about going with a 3.55 ratio rear diff., but my car is NOT sluggish off the line.

My car does feel sluggish if I am puttering around town with the tranni in DRIVE, but then I just click it into SPORT and it changes into a different car!

 

[Zinc03svt]

75-76 mph equals 2000 rpms pp1 3.55 auto.

 

[Grintch]

Someone has way to much free time.....none of it means doodle vs seat of the pants

None of it is relevant to the 10 speed auto discussion either.

The 10A has a very low first gear, so even with the 3.15 gears it has lower gears than pretty much any manual transmission Mustang ever. GT350, Boss 302, old (2015-2017) PP, or even a classic '69-70 Mustang with the 4.30 geared drag pack.

It can easily spin the wheels in 1st, so going to lower final drive just spins the wheels more (which isn't any faster). If the car feels sluggish, it's because you are in the wrong gear or you are too lazy to push the gas pedal down far enough. The best way to fix that is more throttle and a downshift.

As a bonus the 3.15s are good for ~300mph, while the 3.55 is is only good for a measly ~260mph. :-) But of course, you would need to disable the limiter and add a couple thousand horsepower to get there (which would likely be too much for the stock transmission).

 

[WildHorse]

None of it is relevant to the 10 speed auto discussion either.

Then by all means show it for the a10 :doh: And anybody worth their salt knows OD speeds are theoretical.

 

[Jetnoise]

.....And anybody worth their salt knows OD speeds are theoretical.

So the A10 doesn’t employ lock up?

 

[DickR]

So the A10 doesn’t employ lock up?

It locks up. I assume by "theoretical" he meant that the car doesn't have anywhere close to enough power to get anywhere close to redline in the overdrive gears.

 

[Jetnoise]

75-76 mph equals 2000 rpms pp1 3.55 auto.

‘18 PP1 3.73 Six Speed
70mph @ 1970rpm

 

[Grintch]

It locks up. I assume by "theoretical" he meant that the car doesn't have anywhere close to enough power to get anywhere close to redline in the overdrive gears.

Which is pretty much exactly what I said.

But of course, you would need to disable the limiter and add a couple thousand horsepower to get there (which would likely be too much for the stock transmission).

 

[Bald Menace]

back in 2011 when the Coyote Mustang first came out and had the 6R80 the 3.15 was the gear to have and the auto was faster than the 6 speed with any factory gear by a good margin. I had one and it definitely wasn't a slug off the line, i'm sure the A10 and the new Coyote are much better. I have PP1 3.55 A10 and sometimes feel first gear is too steep.

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