In die casting, runner layout takes most of casting part performance and defects. Because it delivers molten from plunger and transport into cavity. So proper runner layout is needed, when you do not take account the shape correctly, might it will bring you to significant defects due to air entrapment.
One of the example shown below. There is poor runner design that leads to heavy air entrapment to the cast. The air pocketing due to runner shape design and turbulence occurred. Even it can colds the molten even faster and creating another problems like a cold shut or flow mark. If temperature drop, likely good cast will never be achieved then.
So optimizing runner shape is a must for this kind of problems. I added air catcher to the top-end of the runner. Letting undesirable air to be trapped inside and just deliver good molten to the cavity. Take a look before-after comparison.