Through their research both in the shop and at the track, the team at Gearstar Performance Transmissions has identified any weak links in the NAG1 and corrected them so their transmissions can withstand 1,100 lb-ft of torque, far more torque than a factory unit is capable of enduring. Each transmission is fully disassembled and cleaned, and then all of the tolerances are checked and corrected before the transmission is assembled using heavy-duty components. All of the internal parts are cryogenically treated and stress relieved, and the second, third, and fourth gear clutch drums are modified for expanded capacity. Gearstar uses high-energy clutches, updates the input-to-output shaft bearing support, and uses a special sprag assembly. Internal fluid pressure is increased for proper lubrication as well.

To control the transmission, the valve-body is reprogrammed and new electronics are installed. A billet torque converter is designed for each application, featuring a custom stall speed and CNC machined precision. The lockup clutch is also modified for increased capacity, which improves durability as well as performance. Once we got our new transmission, we headed up to Inline Performance Specialists in nearby central Florida to get a hand installing the unit. With the help of the technicians at Inline, we had our transmission and converter swapped in an easy half day and were ready for a test drive.

Our first impression of the Gearstar NAG1 was a much crisper overall feel. When the gear selector was placed in a forward or reverse gear, we felt the transmission engage firmly, and throttle response was crisp when driving in any gear. After a little moderate cruising to allow everything to come up to temperature, we ran the transmission through its paces and were pleasantly surprised. The transmission has firmer up and downshifts than the stock transmission, though the shifts are still comfortable and not abusive. The converter is definitely looser as well, allowing tire spin at just about any point through first and second, indicating we’ll need some stickier tires before doing any real track testing. Thanks to the looser converter and tighter transmission, throttle response is noticeably better, and the car is more reactive to throttle input whether part or full throttle.

We know this transmission and converter package have made our Challenger quicker just by the sensation we get from driving the car. It would be a shame to do any track testing with our factory tires, however, as the inevitable tire spin wouldn’t allow us to show you the real improvements we’ve made. Look for a future article as we upgrade the wheels and install stickier tires on our Challenger, and we’ll take our late-model muscle car to the dragstrip for some real testing.