Head Stud Kit
High Performance 8740 Series
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, theres 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. 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
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
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
Premium quality heat-treated 8740 chrome moly steel head stud
kits are available for most every domestic and import
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 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
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.