After reading the post by old iron and seeing the afermentioned term "porpoising", I must say my car does this horribly. I was racing this weekend and my racing partners are continually telling me the car is unloading and porpoising. I have a 67' Barracuda with SS springs, non adjustable mopar 452914 rear shocks, about a 1"+ lowering block, and an adjustable pinion snubber that is touching at the lowest possible setting. I have .870 torsion bars and C/E 3 way adjustable shocks that seem to be a mystery where they are set. The car has a big block, I drove to the track and ran a 10.59 but with a horrible 1.630 60' time on nitrous. This weekend my tires showed little to no holes in the treads and they are spent, the car has went from a 1.69 non nitrous 60' to a 1.73 and still running a 7.20 1/8 mile at 99 mph. I checked the shocks length at ride heigth and they are 16"..... is this where the 452914 mopar shock is supposed to operate. I will be getting a new set of slicks for my August 4th weekend race and hope to get the porpoising fixed, I expect its the rear shocks, I have to get this problem fixed! Im putting down what I think is 700 horse and cant seem to get a good 60' and this porpoising is horrible, im disappointed its not pulling a wheelie