N H R A rules state that the loop must be installed no more than 6 inches behind the front U-joint. If you don't mind more holes in the floor, it's a good idea to install one in the rear as well. See ...

The NHRA requires any car running slicks to have a driveshaft loop, but it's a good idea to put one onanycar, even one that will never see a track. A loop catches the driveshaft in the event of ...