Head studs hold your head and block together. As you make more power than your engine was designed to hold from the factory, the head and the block push apart from each other, stretching the factory bolts and causing various failures. ARP Head Studs are stronger than the factory fasteners and are designed to keep your race engine together under any circumstance. https://www.ebsracing.com/ARP%20Head%20Stud%20Kit%20for%20Porsche%20911-930