how does the big range rover have more horsepower then the sport? Are they not the same engines? I am talking about the 4.2 and 4.4, is there an easy way to add that extra horsepower to the sport?

Many things can impact the measured/advertised horsepower, including exhaust designs. Anyway, you need to stop being a slave to the horsepower specification. It really is pointless unless you are comparing the exact same vehicle.