4 miles is longer than it sounds. I just did a 3.2 mile prologue last weekend (8-9 minute course for most) and it was a much harder/longer effort than I was expecting. Don't blow up on the first few corners.
I also did a similar course to the one you are doing but it was about half the distance. Like Kensuf said, pre-scouting/riding the course is the best way to go. With all those corners, if you can save a 1-3 seconds on each corner over the rest of the people, it adds up. The only way to know how hard or fast you can do those corners is by doing them ahead of time.
Good luck! Remember to suffer and you'll be fine!
