Shipping Built does not use all cores of Quadcore ---- how to do this?

When I package to a shipping built and start it with the .exe in the created folder, then I notice that it always only uses at best 50% of my cpu (task manager).
Is there an easy way to tell UE4 that I want to use all cores before packaging?
It is especially holding back physics simulations, where as much cpu as possible is required.
The question is basically how to set up multi-threading if it is not included already.

(UE 4.6.1)

Is your game running slowly?

yes, there is a massive frame rate drop as soon as physics kicks in (on 1600 stacked crates). Still not more than 50% cpu usage at best.