Your brats should be grilled slowly over medium-low heat (between 300 and 350°F) for the best results. It should take about 20 minutes to hit your desired internal temperature of 160°F. That should take about 20 minutes depending on the thickness of the brats. Remember to turn them often so each side gets caramelized.
Trying to rush the process by using high heat is a cardinal sin in the bratwurst world. Too much heat is going to char the outside and cause the casing to split open, which will allow the juices to spill out.