You can't change the number of turns lock-to-lock unless you change/alter the steering box. What will change is the effort it takes to turn the wheel.

Installing larger (wider) tires will make the steering heavier, so if you are planning to use bigger tires keep that in mind.

No matter what you do, you are not going to get the feel of fast rack and pinion steering or variable ratio steering like a Vette. I don't think the stock feel is that bad specially once you add bigger rubber. The power steering boost is moderate.