Obtaining the optimum cylinder head-to-block sealing is especially critical in small displacement engines employing high compression pistons or power adders like turbochargers, nitrous oxide and superchargers. That’s why ARP head studs are popular among leading Sport Compact/Import racers.
You should know that ARP uses a premium grade 8740 alloy that is rated far superior to “aircraft” quality. Then, each stud is precisely heat-treated to 200,000 psi. Following heat-treat, each stud is centerless ground to make it as close to perfectly concentric as possible. This procedure involves about ten very slight cuts and results in an exceptionally straight part. It’s important to note that lesser quality studs are not even centerless ground – the material is thread rolled in bar stock form (mostly before heat-treat, when the material is easier to machine). Because ARP studs are manufactured to such exacting tolerances, you will note that gaskets and cylinder heads literally glide into position and are perfectly aligned – something that won’t happen with inferior quality head studs.
ARP studs are thread rolled after heat-treat, which gives them about 1000% (that’s ten times) better fatigue strength than those studs that are threaded prior to heat-treat. You will also note that ARP offers specially undercut studs for several engines. This procedure (done only to the shorter studs) more equalizes the “stretch” of both studs, which makes for a more consistent clamping force – one that compensates for head gasket compression when the head is installed. This helps prevent blown head gaskets, and assures optimum sealing!
Premium parallel ground washers are also included with each kit.
ARP Head Bolt Kits are offered in two configurations for optimal performance.
HIGH PERFORMANCE SERIES
High Performance head bolts are made of 8740 chrome moly and available with a reduced wrenching hex or 12-point with a wide area flanged head. They are nominally rated at 180,000 psi and kits come complete with hardened parallel-ground washers.
PROFESSIONAL SERIES
All Pro Series bolts are designed for competition applications and are rated nominally at 200,000 psi. Available with undercut short bolts that can help eliminate head gasket failures through providing more “stretch” to balance the longer bolts and compen.