In a recent article written for Hot Rod Magazine, I dove into the finer points of how modern 6/8/10 speed automatic transmissions work so well to keep the engine right in the sweet spot for acceleration. They often do this with the torque convertor locked most of the time. This means we only care about the slip RPM (K-Factor) right off the line, where traction is often a challenge anyway. The same actually holds true for when we’re looking for peak fuel economy, but who can think of that when we have drag races to win? With more ratios to choose from, the game has changed.
Nailing the example, I used some datalogs from a friend’s 9-second street car to show just how well a modern 8-speed automatic runs.
As long as we’ve done our job mapping the engine correctly, these modern transmissions do a great job of executing quick shifts that put the engine right where we want it almost all the time. Better yet, they do this without needing a change to the torque convertor to something that trades more power for slip.