All I can say is that they are working very well. At the moment I'm running 2-AC F12s and 2-SS H12s. The F12s run at 100% all the time but don't have a tach wire so I don't know what rpms they are turning. What I do know is that the H12s @ 1500 rpm move more air and are at least as quiet as the F12s. Then they can rev up over 2200 rpm where they are still not loud. I would like to get 2 more or their equivalent. Or just get 4-2150 rpm GTs.