THE MERCEDES-DESIGNED automatic trans designated NAG1 (New Automatic Gearbox, Gen 1), and/ or W5A580, is a Chrysler-built (and upgraded) version of the original M-B 5G-Tronic tranny, an electronically-shifted 5-speed overdrive automatic transmission with torque converter lockup. It was used behind 5.7L, 6.1L, and 6.4L Hemis in passenger cars (read: 300, Challenger, Charger) through 2014, and is still used, for example, in all cop cars (column-shifted), and some Durangos, the old Dodge-labeled Sprinter vans, etc.
At any rate, one thing we learned the first time we power-braked one of these Hemi-powered cars at the drags is this: the stock torque converter is pretty lame. Like, a 2250 RPM stall lame. That isn’t gonna really get this—or any—car down that 60-foot chute in any kind of a hurry. So we began investigating…