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.
Factory fasteners were not designed for performance use. The material chosen by the Original Engine Manufacturer for your engine's factory fasteners was chosen to meet the criteria of a normally driven consumer vehicle at the provided stock horsepower and rev limit. The material is not optimum for a high reving, high heat, high power, race car.
The factory fasteners were also not designed to be reused. Every time you torque a fastener, it stretches to perform the proper clamping force. If the fasteners stretch too far, they will not longer provide the required clamping force, and can lead to an engine failure. When you take your factory engine apart to build it into your race engine, discard your used factory main bolts and switch to a brand new set of ARP Head Studs to provide your engine with the proper clamping force required to keep all of your parts together in the harshest race environment.
We have seen heads lift and blow head gaskets, pressurize the cooling system, and worse. ARP Head Studs are a very inexpensive part that couldn't be more important to your engine build. Consider them a must.