The variable timing control for both intake and exhaust cycles improves low - end engine response. (cheersandgears.com)
The DOHC design provides exceptional valve timing control to deliver high peak horsepower and low - end torque. (usedcarsgroup.com)
These were all filed around the same time in the late 80's and early 90's, it looks like there was probably a big patent rush for ignition timing control systems. (mechanics.stackexchange.com)