ARP Head stud kits

ARP’s cylinder head kits are either stud kits or bolt kits, and that is the first decision. A stud kit goes into the block finger-tight, using the Allen socket in the top of each stud. The head is then clamped by tightening nuts, so the block threads take no twisting load as the fastener stretches. A bolt kit replaces the original head bolts one for one, which suits an engine that stays in the car with little room above the head.

Many kits are specific to a cylinder head as well as a block, including aftermarket castings, and some use undercut studs, whose shank is reduced to the root diameter of the thread. The listings give the nut or bolt head style (12-point or hex) and the socket size. Some also name the alloy: 8740 chrome moly or ARP2000 in most cases, and Custom Age 625+ on a few kits.

A few kits also carry vehicle fitment, mainly for Nissan, Honda and Toyota models such as the Silvia and Skyline, the S2000 and the MR2. For the rest, go by the engine, head and block named in the title, and tighten in stages in the engine maker’s sequence.