ARP Head Studs - WRX/STi EJ2.0/2.5L
It is for good reason that virtually every top professional engine builder relies on ARP Pro Series head studs for their all-out competition powerplants. 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 manufacturers who just dump pieces in a basket and hope for the best.
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 (a very common industry practice). It costs a lot more to do it this way, because it's tough on tooling, but the results are well worth the extra effort.
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 - and one that compensates for head gasket compression when the cylinder heads are installed. This helps prevent blown head gaskets, and assures optimum engine sealing!
Premium quality heat-treated 8740 chrome moly steel head stud kits are available for most every domestic and import applications. You won't find a better quality stud on the market from any other source. Look for ARP stamped on each stud as your assurance of quality.
In the box:
12 X Set of ARP Head Studs - 11mm
12 X Parallel Ground Washers
12 X Chrome Moly Steel 12 Point Nuts
1 X 1/2oz pack of ARP Ultra-Torque fastener assembly lubricant