4 Piston Racing Head Studs. Whether you are pushing an additional 100hp or 500hp over stock with your K20C1, optimum cylinder head to block sealing is critical. 4P head stud bolt set are premium grade 8740 alloy and are precisely manufactured to the highest quality standards. If you plan on turning up the boost and pushing the limits, don't forget this critical part of your build. Manufactured by ARP, exclusive to 4 Piston Racing.