Upgrade your 2008-2010 Ford 6.4L Powerstroke with this Head Stud Kit. It's a proven fact that OEM head bolts are the weak link in a diesel engine; especially if the engine has been modified. That's because most engines are typically assembled from the factory using Torque-To-Yield (TTY) bolts and preloaded to yield and beyond (typically 100-110%). Any increases in combustion pressure can lead to problems like blown head gaskets or catastrophic engine failure and because TTY bolts are yielded by design, they should never be re-used.