Gearing Equivalents

[TheLion]

Manuals:

3.31 Speed Engine RPM
4.236 40.12 MPH 7000
2.538 66.96 MPH Tire Height (in.)
1.665 102.07 MPH 27
1.238 137.27 MPH
1.000 169.94 MPH
0.704 241.39 MPH



3.55 Speed Engine RPM
4.236 37.41 MPH 7000
2.538 62.43 MPH Tire Height (in.)
1.665 95.17 MPH 27
1.238 127.99 MPH
1.000 158.45 MPH
0.704 225.07 MPH



3.73 Speed Engine RPM
4.236 35.60 MPH 7000
2.538 59.42 MPH Tire Height (in.)
1.665 90.57 MPH 27
1.238 121.81 MPH
1.000 150.80 MPH
0.704 214.21 MPH

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[TheLion]

Autos (assuming 10% converter slip which is typical):

Rear Axel Ratio 3.15 Speed Engine RPM
1st Gear Ratio 4.170 38.54 MPH 7000
2nd Gear Ratio 2.340 68.68 MPH Tire Height (in.)
3rd Gear Ratio 1.520 105.73 MPH 27
4th Gear Ratio 1.140 140.98 MPH
5th Gear Ratio 0.870 184.73 MPH
6th Gear Ratio 0.690 232.92 MPH



Rear Axel Ratio 3.55 Speed Engine RPM
1st Gear Ratio 4.170 34.20 MPH 7000
2nd Gear Ratio 2.340 60.94 MPH Tire Height (in.)
3rd Gear Ratio 1.520 93.82 MPH 27
4th Gear Ratio 1.140 125.09 MPH
5th Gear Ratio 0.870 163.91 MPH
6th Gear Ratio 0.690 206.67 MPH



Rear Axel Ratio 3.73 Speed Engine RPM
1st Gear Ratio 4.170 32.55 MPH 7000
2nd Gear Ratio 2.340 58.00 MPH Tire Height (in.)
3rd Gear Ratio 1.520 89.29 MPH 27
4th Gear Ratio 1.140 119.06 MPH
5th Gear Ratio 0.870 156.00 MPH
6th Gear Ratio 0.690 196.70 MPH

3.55 Auto is roughly equivalent (just a tad lower geared) to a 3.73 Manual. 3.73 Auto would probably be too short gearing. In 4th a 3.55 can trap up to 125, in 4th a manual can trap up to 122, assuming a 7k cut off for both.

I know people have mulled putting in a 3.73 in an auto, but I think a 3.55 is probably more optimal. 3.73's work well though in the manual as your pegged to each gear, there's no converter slip (also slip changes, at lower RPM your have more slip = torque multiplier, some converters can multiply up to 2:1 before stall, but I"m not sure what the 6R80's spec is).

 

[hungryhippos]

I know people have mulled putting in a 3.73 in an auto, but I think a 3.55 is probably more optimal. 3.73's work well though in the manual as your pegged to each gear, there's no converter slip (also slip changes, at lower RPM your have more slip = torque multiplier, some converters can multiply up to 2:1 before stall, but I"m not sure what the 6R80's spec is).

This crossed my mind after seeing the 3.73 EB conversion thread, thanks for sharing your insight!

 

[TheLion]

When the numbers are worked out, I think what Ford was trying to achieve is utilizing the low end torque the EB makes more often. Given how the factory PCM software as a very low torque goal in the upper rpm range (combined with the IC deficiency), there's really no reason to run a bone stock EB in that range. Taller gearing makes sense and w 3.73's were not considered a factory option even though manual tuned EB's with a good FMIC do very well with that gearing and it's roughly equivalent to the auto with a 3.55.

The low end torque is still useful with 3.73's even if it's not utilized as much (especially for DD), it's useful for getting off the line or getting the car going after a shift (when the RPM drops into the 4k range) in the first two gears. Here's a shift point chart for MT-82 and 3.73 I created based on LMS dyno (to get an approximation of where I should shift to keep the most area under the curve for each gear change):

Optimal Shift Points End RPM Start RPM End Power Start Power
1st - 2nd 7000 4200 290 HP 275 HP
2nd - 3rd 7000 4600 290 HP 290 HP
3rd - 4th 6350 4725 300 HP 305 HP

Obviously this is not exact and would need to be tested, but based on the RPM drop (less the higher the next gear obviously as the ratios become closer and closer), shift points are different at different RPM's.

First two gears it makes sense to rev it out to keep the most area under the curve, but 3-4 makes more sense to shift a bit earlier to keep the RPM centered around the power curve.

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