so I input the various ratios available for the 2 transmissions offered into a gearing/mph calculator to give an idea of the speed@1000 rpm.

pick your motor, trans., tire size and ratio to see what rpm's you will be turning at any given speed.

MUSTANG GT
235/50/18 tires
MT ratio rpm 1st 2nd 3rd 4th 5th 6th
3.31 1000 7 10 14 19 24 38
3.55 1000 6 9 14 17 23 35
3.73 1000 6 9 13 16 22 33

245/45/19 tires
MT ratio rpm 1st 2nd 3rd 4th 5th 6th
3.31 1000 7 10 15 19 25 38
3.55 1000 6 10 14 18 23 36
3.73 1000 6 9 13 17 22 34

255/40/19 tires
MT ratio rpm 1st 2nd 3rd 4th 5th 6th
3.31 1000 7 10 14 18 24 37
3.55 1000 6 9 13 17 23 35
3.73 1000 6 9 13 16 22 33

235/50/18 tires
AT ratio rpm 1st 2nd 3rd 4th 5th 6th
3.15 1000 6 11 17 23 30 37
3.31 1000 6 10 16 21 28 35

245/45/19 tires
AT ratio rpm 1st 2nd 3rd 4th 5th 6th
3.15 1000 6 11 17 23 30 38
3.31 1000 6 11 16 22 29 36

Given the 7000 rpm redline:
MANUAL TRANS cars will cross the 1/4 mile in 4th gear.
AUTO TRANS cars will cross the 1/4 mile in 3rd gear unless it can exceed a 112mph trap speed.

MUSTANG V-6
215/65/17 tires
AT ratio rpm 1st 2nd 3rd 4th 5th 6th
2.73 1000 7 13 20 27 35 44

235/50/18 tires
AT ratio rpm 1st 2nd 3rd 4th 5th 6th
2.73 1000 7 13 20 26 34 43
3.31 1000 6 10 16 21 28 35

225/60/17 tires
MT ratio rpm 1st 2nd 3rd 4th 5th 6th
2.73 1000 7 12 18 24 30 43
3.31 1000 6 10 15 20 25 35

235/50/18 tires
MT ratio rpm 1st 2nd 3rd 4th 5th 6th
2.73 1000 7 12 18 24 30 42
3.31 1000 6 10 15 20 24 35

All the V-6 cars should cross the 1/4 mile in 3rd gear unless it can exceed a 105mph trap speed.

 

Exactly why I would go with 4.56 or 4.88 rear end gears if I bought an '11 GT Automatic. I had already done the math and I'd want to go through the traps in 5th (closest gear to a 1:1 ratio) to use as much torque multiplication as possible. 4.88 gears would allow for trap speeds of nearly 115 mph in 5th, which is more than enough for a stock '11 GT Automatic, IMO. Maybe 4.56's if I thought I'd be adding a blower later on.

 

How about showing it for a more usable RPM, say 2,500?

 

I think he did 1000 RPM as a simple baseline so you could calculate speeds at different RPM's with simple multiplication (I.E. MPH x 2.5 for 2500 RPM).

Doug

 

Here is a really slick speed/rpm calculator. Plug in all the gear ratios, tire size and top RPM and it gives you the speed in each gear by RPM in 100 RPM incriments.

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

6R80/6R60 gear ratios

1st: 4.17, 2nd: 2.34, 3rd: 1.52, 4th: 1.14, 5th: 0.86, 6th: 0.69

MT82:

_______V6 / V8
1st: 4.236 / 3.66
2nd: 2.538 / 2.43
3rd: 1.665 / 1.69
4th: 1.238 / 1.32
5th: 1.00 / 1.00
6th: 0.70 / 0.65

Plug the numbers into the calculator and it will surprise you!

_______

 

These are the numbers I like to look at, top speed in each gear at 7000. Never mind sixth though, it'll never pull 7K in 6th.

7000 - 1st: 49, 2nd: 74, 3rd: 107, 4th: 136, 5th: 180, 6th: 277

Think it'll make 180 in fifth???

 

That's a good question... I wonder what the aero limit of this body/hp combination is (without the speed limiter)?

A friend of mine said they had a mule (production variant) at 140 in sixth gear at half throttle... Now, I've done redneck math before, but I can't get there from here.

 

I think its possible with the GT. The SRT8 was making 173 with an automatic. The SRT8 is a lot big and a brick so I think its possible.