It looks correct to me. You can try to make a simpler demo of your game/engine and test only rotation, perhaps you have some other variable affecting the rotation that you haven't considered?
Can you post some runnable code/demo?
Can you post some runnable code/demo?
your limits i.e. TurnMax and TurnFriction have to take the Deltatime into account, they can't be constant nomatter the current frame rate.
I can't agree. Max values and Friction Max/Min should be constant over framerates and measured in pixels/second. Ex your engine's topspeed is = 400 (pix/sec). No delta here.