They did more than "add another fan". Here's a quote from the below link: H70 "The Hydro Series H70 is an evolution of the award-winning Hydro Series H50, with several significant upgrades that enable it to deliver even greater cooling performance. These upgrades included a thicker 120mm radiator unit (50mm) with a higher heat-exchanging capacity, and a more efficient, low-profile pump/cold-plate unit that can soak up more heat and provide even lower CPU temperatures." See Corsair Blog "To start with, we doubled the thickness of the radiator. Increasing the surface area of your heat exchanger is one of the best ways to increase heat dissipation in any cooling setup. By increasing the radiator thickness, we were able to boost performance without significantly affecting compatibility. When you go to a thicker radiator, it’s almost a sin to starve it for airflow. So for the H70 not only did we add a second fan, but better yet we upped their performance as well. The fans that come with the H70 up the speed of the H50 fan from 1700RPM to max of 2000 RPM. The dual fan setup gives you push-pull compatibility out of the box."