The BIOS doesn't allow me to change settings, but shows me that the max clock should be 2,5GHz. I already tried different power saving settings of my PC and battery-configurations. But I don't really want an off-site tool two boost my CPU, when it should do it by itself.
I tried them all and also different Windows Versions but nothing helped, until I forced the multiplier to 25 with ThrottleStop, which was working really well. Acer already released special drivers and a BIOS activating the turbo boost. I've got some troubles with my Acer Aspire E5 571G with an intel i5 5200U and a nVidia GT 840m: Because of the poor performance of my system, I checked the CPU clock under stress and noticed, that the highest clock achieved was 2,2 GHz (measured with CPU-z and intel Tuning utility) when two cores were used.