These new single valve springs deliver 15% more pressure accross the board than the OEM springs. Also, with a coil bind of 0.910", the Crower spring allows for more cam lift than factory springs will allow. These are the stock O.D., so no machine work is required to the cylinder head. The Crower titanium retainers weigh in at 7 grams vs. stock steel at 14.5 grams. So you can pick up additional rpm's by reducing valve train weight.