[SILVER BULLET]

Twin cam heads {1999-2004 } have a 'NEW' valve spring pressure of 100 lbs. - + 3 at the installed heigth. 2005-2006 single spring {beehive} have 137lbs. - + 2 This is something to think about. Notice that I said NEW springs. When the motor gets 20,000+ miles on it,the spring pressure goes down.

 

[Don Dorfman]

Seat pressure is just one part of the story. The spring rates are about the same and at mid lifts the pressures become close to equal. Single beehive VS dual conventionaly wound valvesprings