ARP Cylinder Head Studs
It is for good reason that virtually every top professional engine builder relies on ARP Pro series head studs for their all out competition power plants. Simply stated, there's not a better stud setup on the market today.
For openers, ARP uses a premium grade 8740 alloy that is rated far superior to "aircraft quality". Then, each stud is placed vertically in special racks and precisely heat treated to 200,000 psi. This procedure ensures complete heat penetration and the results are far superior to those lesser quality studs from other manufactures who just dump pieces in a basket and hope for the best.
Following heat-treat, each stud is center- less ground to make it as close to perfectly concentric as possible. This procedure involves about 10 very slight cuts and results in a very exceptionally straight part. It's important to note that lesser quality studs are not even center- less ground- the material is thread rolled bar stock (Mostly before it's heat treated because it's easier to machine). Because ARP studs are manufactured to such exacting tolerances, you will note that gaskets and cylinder heads glide into position and are perfectly aligned- something that wont happen with inferior quality head studs.
ARP studs are thread rolled after heat treat, which gives them about 1000% (That's 10 times) better fatigue strength than those studs that are threaded prior to heat treat (A very common industry practice). It costs a lot more money to do it our way, because it's tough on the tooling, but the results are well worth all the extra effort.
You will also note that ARP offers specially undercut studs for many engines. This procedure (Done only to the shorter studs) more equalizes the "stretch" of both studs, Which makes for a more consistent clamping force- and compensates for head gasket compression once the heads are installed. This helps prevent blown head gaskets, and assures optimum engine sealing.
Premium quality heat treated 8740 chrome-moly steel head studs are available for most every domestic and import application. You won't find a better quality stud on the market from any source. Look for ARP stamped on the end of each stud as your assurance of quality.
ARP head stud kits are available with your choice of conventional hex nuts, or compact 12 point nuts. Premium quality parallel ground washers are also included with each kit.
Head Studs Vs. Bolts: A Technical Discussion
ARP's factory tech rep's are often asked which is better, cylinder head studs or bolts. The answer invariably, depends on the installation. On many street driven vehicles, where master cylinders and other items protrude into the engine compartment, it's probably necessary to use head bolts so that the cylinder heads can be removed with the engine in the car.
For most applications, however, studs are recommended. And for good reason. Using studs will make it much easier to assemble an engine (especially a racing power plant which must be serviced frequently and quickly). With the cylinder head and gasket assured of proper alignment.
Studs also provide more accurate and consistent torque loading. Here's why. When you use bolts to secure the head, the fastener is actually being "twisted" while it is being torqued to the proper reading. Accordingly, the bolt is reacting to two different forces simultaneously. A stud should be installed in a "relaxed" mode- never crank it in tightly with a jamb nut.
If everything is right, the stud should be installed finger tight. Then, when applying torque to the nut, the stud will stretch only on the vertical axis. Remember, an undercut shorter stud wil