cariacou

dang... so that would basically mean 140mph *4.10/2.73 = 93 mph ?

no, that can't be true

Chromeshadow

Here's my calculations for the 4:10 with a Manual Trans:
RPM -- Speed -- Gear -- Drive shaft speed
6850 -- 146mph -- 5th -- 6850 rpm
5400 -- 150mph -- 6th -- 7714 rpm

btw, The drive shaft is probably rated for the worst case with a factory set up...120 mph with the 3:31 which is about 5,000 RPM in 5th with the drive shaft turning at 5,000 rpm (5th in the manual is 1:1). Taking the drive shaft to 7714 rpm sounds like a huge risk to me.

Norm Peterson

Computing a theoretical speed at any given rpm in each of those axle gears is pretty simple.

What isn't as easy is calculating ahead of time whether your car can reach any particular target speed that you have in mind. Or what gear you'd need to have the tranny in so that the engine would be at an rpm that makes at least the minimum required power to be up there. Tire size makes a difference, too.

Sorry, but there isn't nearly enough information for me to even take a shot at providing any numbers even though I have a spreadsheet that has the capability to do what you're asking for.


Norm

cariacou

can I have the spreadsheet ?

my tires are 285/30/20 & 255/35/20, rest of the car is stock atm. what extra information do you need ?

Norm Peterson

I'm afraid that I'd end up having to answer too many questions. Here's what about half of the input plus some summarized results looks like.

Much simpler if you give me engine peak torque & rpm, peak HP & rpm, and the transmission model name/number. With some information I have elsewhere that'll be close enough.


Norm

cariacou

Here's what I was able to find:
and the transmission is a Ford 6R80 (6-speed automatic)


hope that's enough

sources:
http://en.wikipedia.org/wiki/6R80http://wot.motortrend.com/mustang-po...#ixzz2S9sAB8Gj

Norm Peterson

Fitting a torque curve to those actual numbers, using 3475 lbs for the car and 175 lbs for the driver . . . mph to highest whole mph and rpms to nearest 50 rpm looks like this. Chances are the 150-ish numbers are all slightly high estimates, as I was not assuming significant drivetrain losses, which costs something like 5 - 8 mph. So I tried 88% drivetrain efficiency, which I think is closer to reality.

Axle . . . mph . . . rpms . . . gear . . . 88%mph . . . 88%rpms . . . gear
3.55 . . . 151 . . . 6050 . . . 5th . . . . . 142 . . . . . . . 5700 . . . . . . 5th
3.73 . . . 151 . . . 6350 . . . 5th . . . . . 144 . . . . . . . 6050 . . . . . . 5th
3.90 . . . 151 . . . 6650 . . . 5th . . . . . 144 . . . . . . . 6350 . . . . . . 5th
4.10 . . . 150 . . . 6900 . . . 5th . . . . . 144 . . . . . . . 6650 . . . . . . 5th

6th gear is too tall and will not reach the same speeds as 5th will regardless of the axle gearing.


And for comparison,

2.73 . . . 151 . . . 6100 . . . 4th . . . . . 143 . . . . . . . 5800 . . . . . . 4th


What you need to know is that the last few mph take forever to be added, and every time you so much as breathe off the throttle you just threw away the last anywhere from quarter mile to well over half a mile worth of acceleration. Any small upward slope will likewise cost you distance or ultimately top speed itself. In at least one of the above cases, the very last mph takes over a mile to add.


Norm

cariacou

thank you Norm ! This is very useful data.

yeah the drive shaft, especially on the 2011-2013s v6 is unefficient. I will replace this soon and hopefully remove some of the losses.

I have one last question, what did you mean by
do you mean that the car is not using the 6th gear when going in high speeds ?

CMcNam

Dang, glad you understood that. I just saw a bunch of numbers and my head exploded. I don't maths.

Sorry for the threadjack.

cariacou

hahaha