You can either make a corkscrew loop, or a jump up and through itself sorta loop (use a helper to avoid a bonk), in both cases using a plastic block as the final block of the loop helps the exit.

Also be sure that all the bumpers are going in the same direction -- or be aware that there are 2 possible directions for each position it can be in.

Additionally, if you go through such looping backwards, you get hella speed.