Because I'm a tech writer, I live in a world full of horsepower curves and gear ratios. So news about the GM six-speed 6L80E and 6L90E automatic transmissions is of major interest. Yes, they're big—they're even heavier than the bulky 4L80E automatics. But these boxes also added two more gears. That places the rpm drop between gears much closer together. These boxes are also a departure from the traditional band- and clutch-type automatics in that these are clutch-to-clutch transmissions. This means there can be no overlap between clutch release and clutch apply for the next gear. Another odd part of these gearboxes is that the PCM (powertrain control module) is located in the oil pan. Gear ratios fall this way: First 4.02:1, Second 2.36:1, Third 1.53:1, Fourth 1.15:1, Fifth 0.85:1, Sixth 0.67:1. The first big surprise is that there is no 1:1 ratio perhaps because Fourth and Fifth are so close together. Weight is certainly a consideration, since GM puts the wet mass at 212 pounds. Also, based on the very deep 4.02:1 First gear ratio, you won't need more than a 2.73:1 rear gear ratio. Doing the math, a 2.73:1 rear gear with a 4.02:1 First gear produces the same effective First gear ratio as a TH400 with a 4.42:1 rear gear. In Sixth gear, that will also produce a Bonneville-like 1.83:1 cruising gear. We know of a couple of builders who are using these trannies and there are a couple of companies already on the Internet selling transmissions. We've come a long way from Powerglides, baby.