SKU: ARP260-4301 (FA20)
For openers, ARP uses a premium grade 8740 alloy that is rated far superior to aircraft quality. 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. Its 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 wont happen with inferior quality head studs.
ARP studs are thread rolled after heat-treat, which gives them about 1000% (thats 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 its 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 wont find a better quality stud on the market from any other source. Look for ARP stamped on each stud as your assurance of quality.
Clearly, ARP Head Stud/Bolt Kits are the best on the market today, and the favorite of leading professional engine builders in all forms of racing.
- HIGH PERFORMANCE SERIES
- High Performance head bolts are available with a reduced wrenching hex or 12-point and wide area flanged head that eliminates the need for valve train removal to facilitate cylinder head retorquing. All High Performance Series bolts are 180,000 psi (which is 15% stronger than Grade 8) and kits come complete with hardened parallel-ground washers.
- PRO SERIES
- All Pro Series bolts are cold-forged to ensure molecular integrity, heat-treated prior to thread rolling and machining, and are rated nominally at 200,000 psi. ARP Pro Series head bolt kits are application specific - designed for use with typically competition only components. These fasteners deliver superior strength and meet the ARP ZERO defect - ZERO failure quality standard. Hardened and parallel-ground washers are included with each kit to ensure even load distribution and accurate torque readings. All Pro Series head bolts have a reduced wrenching hex or 12-point head and wide area flange to eliminate the need for valve train removal for cylinder head retorquing and permits the use of larger diameter valve springs. Most applications have undercut short bolts that can help eliminate head gasket failures through providing more stretch to compensate for the additional compression of gaskets.
- Head Studs vs Bolts
- On many street-driven vehicles, where master cylinders and other items protrude into the engine compartment, its 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 powerplant 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. Heres why. When you use bolts to secure the head, the fastener is actually being twisted while its 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 using a jammed 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 will have a rate similar to a longer, standard shank stud. This provides a more even clamping force on the head. Because the head gasket will compress upon initial torquing, make sure studs and bolts are re-torqued after the engine has been run.
SKU: ARP2604701 (WRX & STi)
ARP2000 is an alloy steel that can be safely heat treated to a higher level, producing a greater strength material than 8740. While 8740 and ARP2000 share similar characteristics - ARP200 is capable of achieving a clamp load at 220,00 psi. ARP2000 is widely used in short track and drag racing as an up-grade from 8740 chrom moly in both steel and aluminum rods. Stress corrosion and hydrogen embritlement are typically not a problem, providing care is taken to protect the parts from moisture and the parts are kept well-oiled.
What exactly is ARP2000 and how does it compare to 8740 and 4340?
ARP2000 is a heavily alloyed martensitic quench and temper steel. It has excellent stability at high temperatures. But most important, ARP research discovered that in addition to temperature stability it has excellent notch toughness in the higher strength ranges and is alloyed to be tempered to the Rockwell C45/47. 8740 and 4340 can be tempered to the same hardness. But the tempering temperature would yield material in the temper brittle zone (between 500* and 700* F), producing significant notch sensitivity. ARP2000 is tempered above that temperature range and has a strength between 200,000 and 220,000 psi.
Following the basic shaping, material is heat-treated to desired levels. This crucial process is done entirely in-house to assure total quality control. ARP uses special vertical racks to hold each piece individually and assure complete 360° penetration. This is far superior to commonly-used methods of dumping items into a large bin and batch-treating.
The thread rolling operation (to MIL-S-8879A Specifications) is done after heat-treat, which accounts for a fatigue strength up to ten times higher than fasteners which are threaded prior to heat-treat.
ARP Head Studs are hands down one of the best products of its kind available on the market.
If you are rebuilding your engine, why not put in the best that is available?
The ARP Part # for these head studs is 260-4701
They Will fit the USDM 2002+ WRX, 2004+ STI, 2004+ Forester XT, & 05-09 Legacy GT