Found this while looking through the service manual (page 21 - 497):
Quote:
NAG1 identifies a family of transmissions and means “N”ew “A”utomatic “G”earbox, generation 1. Various marketing
names are associated with the NAG1 family of transmissions, depending on the transmisson variation being used in
a specific vehicle. Some examples of the marketing names are: W5A300, W5A380, and W5A580. The marketing
name can be interpreted as follows:
* W = A transmission using a hydraulic torque converter.
* 5 = 5 forward gears.
* A = Automatic Transmission.
* 580 = Maximum input torque capacity in Newton meters.
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FWIW, 580 NM = 427 Ft-Lbs. Which also explains why the SRT-8's 6.1 'only' puts out 420 ft-lbs of torque.
(of course, it may be able to take more than it is rated for).