Here are some of the more common 4-speed (overdrive high gear) automatic transmissions. In all cases, 3^rd gear is direct (1.00-1 ratio, as in the original 3-speed on which these are based) and 4^th is overdrive with the driveshaft turning faster than the engine. This involves a certain degree of risk as to driveshaft speed, which would not be present in a car with the same over-all ratio achieved with 1.00-1 high gear and equivalent axle ratio for the same RPM vs. MPH.
    The transmissions are grouped by manufacturer. The “base” is the original transmission case type from which the OD transmission was developed.
    The column next to each gear is the percentage of engine RPM recovered after the shift into this gear. Actual RPM will always be slightly higher due to converter slip. Note that the transmissions with the highest torque in 1^st gear (largest value for “1^st”) also have the worst engine speed recovery, and require the widest power band for successful use.

4-Speed Overdrive Ratios

Trans

Chrysler

GM

Ford

Gear

500

Shift %

518

Shift %

4L80

Shift %

200-4R

Shift %

4L60
700-R4

Shift %

AOD

Shift %

AODE

Shift %

1^st

2.74

2.45

2.48

2.78

3.06

2.40

2.84

2^nd

1.54

56%

1.45

59%

1.48

61%

1.57

56%

1.63

53%

1.47

61%

1.55

55%

3^rd

1.00

65%

1.00

69%

1.00

68%

1.00

64%

1.00

61%

1.00

68%

1.00

65%

OD

.69

69%

  .69

69%

  .75

75%

  .67

67%

  .70

70%

  .67

67%

  .70

70%

Base

904, 999

727

TH400

TH250

TH350

C4

    For reference, here are some common automatic transmissions, note the internal ratios are quite different in some cases.

2 & 3-Speed Ratios

Trans

Chrysler

GM

Ford

Gear

999

Shift %

727

Shift %

TH350

Shift %

TH400

Shift %

PG

Shift %

PG

Shift %

C4

Shift %

1^st

2.74

2.45

2.52

2.48

1.82

1.76

2.46

2^nd

1.54

56%

1.45

59%

1.52

56%

1.48

61%

1.00

55%

1.00

57%

1.46

59%

3^rd

1.00

65%

1.00

69%

1.00

66%

1.00

68%

1.00

65%