Valves and the system around them are of great importance for how many revolutions an engine can take. Original valve spring is not made to take many turns, as tight valve springs take more power and press hard on the camshaft. If you have a very tight valve spring, you must drive at high idle as the oil film that is on the camshaft or can be broken.
But tighter spring you can run with more revolutions on the engine as the valves can be moved faster. If the springs cannot close the valves, they begin to "float" or, in the worst case, hit the pistons and smash the engine.
If you lighten your valve stems by turning some of them, you get a higher flow into the engine and you do not need as much spring force to move the valve quickly. The valve and the valve seat can be machined so that there is a higher flow - Here you have to talk to the company that has to machine the cylinder head.
If you are building a turbocharged engine, do not take too much material from the trunks, as a turbo engine develops more heat. Heat must be led up through the valve seat and the valve stem up into the cylinder head. The intake valve is not heat loaded as hard as the exhaust valve, the intake valve is cooled by the intake air as well as the fuel. An exhaust valve can only be cooled through the valve seat and the stem, and it is affected by heat a lot when it opens for the exhaust gas as still in combustion.
Remember to have a freshly sanded valve seat so that it closes tightly.