As I recall, back in the 50s someone made a shiftable timing gear kit for small block chevys. The gear in the center, between the crank and the camshaft, could be moved back and forth with a choke type cable. The idea was to retard the cam timing for torque, and advance the cam timing for revs. I believe that it was originally developed for added torque to tow trailers through the mountains, but it made it's way to the drag strip.
If that is already common knowledge, bear with me, I haven't been around the scene for many years...LOL