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ARP

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ARP (Automotive Racing Products) has grown from literally a backyard garage workshop into a highly diversified manufacturer with four operational entities in southern California.  These include forging, machining, finishing and packaging/warehousing.  Its product line includes virtually every fastener found in an engine and driveline, ranging from quality OEM replacement parts to exotic specialty hardware for Formula 1, IndyCar, NASCAR and NHRA drag racing applications.  Virtually every major championship on the planet won with engines prepared by ARP customers, e.g., Hendrick Motorsport, Honda Racing, Ilmor Engineering, Alan Johnson Enterprises, John Force Racing, Warren Johnson Ent., Earnhardt/Childress.....  In addition to being the pre-eminent source for serious racers, ARP has an Aerospace Division and is licensed by the United States Government to manufacturer MS-21250 fatigue rated fasteners.   Besides the necessary manufacturing facilities for forging (hot and cold), machining, including grinding and thread rolling, ARP has a state-of-the-art heat treating operation as well as the process capability to polish stainless, black oxide finish and shot peening.  ARP has a fully equipped lab for R&D and quality control.  Everything necessary to ensure that ARP products measure up to the company’s ultra high standards. 

Some of the tests that ARP personnel perform on an ongoing basis, include proof loading (using a 120,000 lb. capability tensile machine), fatigue cycle (Amsler) and hardness (Rockwell).  Visual inspections include use of an Optical Comparator (to check thread root contour, etc.), fixtured micrometers and microscopic grain flow analysis. 

ARP is second to none in the quality of the fasteners they sell and support, and is well worth that extra insurance for those investing time and money in the motors they build.

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Tech Note:  Rod Bolts

Unquestionably the most important fasteners in any engine are the connecting rod bolts, as they hold the key to the entire rotating assembly.  A broken bolt will lead to catastrophic engine failure.  As you can imagine, the most critical joint is where the connecting rod halves mate.  The rod bolts most support the primary tension loads caused by each rotating (or cycle) of the crankshaft.  When the crank rotates, the big end of the connecting rod essentially becomes oval-shaped and the rod bolts bend.  As the crankshaft continues to rotate, the rod becomes round again.  With alternating tension loads and cyclic bending of the bolts, it is very important to install fasteners that are able to exert a clamping force greater than the load imposed upon the joint (tension).

In addition to utilizing a rod bolt with sufficient strength to withstand the tremendous cyclical strains placed upon it, it is absolutely imperative that the bolts be properly tightened.  The preferred method of monitoring the correct amount of tension is through use of a stretch gauge.  This is far more accurate than using a torque wrench.  Moreover, through subsequently checking the rod bolt’s length at tear-downs, it is possible to determine if it has been stressed beyond safe limits and must be replaced.

Rod Bolt Stretch & Torque Specs.

Note, bolts are manufactured from 8740 chrome moly.  Now viewed as only moderate strength, it is seen as a good tough steel, with adequate fatigue properties for most racing applications, but only if the threads are rolled after heat treatment, as is the standard ARP production practice.  Typically chrome moly is classified as a quench and temper steel, that can be heat treated to deliver tensile strength between 180,000 and 210,000 psi.    Stock OEM 4AG rod bolts have been tested at less than 160,000 psi.  Test results on file at Toysport.

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Tech. Note:  Head Studs vs. Bolts

The use of head studs in place of head bolts invariably depends on the installation.  On many street-driven vehicles where master cylinder and other items protrude into the engine compartment, it’s probably necessary to use head bolts so 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 assembly 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.  Here’s why.  When you use bolts to secure the head, the fastener is actually being “twisted” while it’s 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.

Head Studs

ARP uses a premium grade 8740 alloy, precisely heat treated to 190,000 psi.  Following heat treat, each stud is centerless ground to make it as close to perfectly concentric as possible and thread rolled after heat treatment which gives them about 1000% better fatigue strength than those studs that are not.

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Tech. Note:  Main Studs

There are many important reasons to use ARP main stud kits, including the elimination of main cap walk and fretting, as well as protecting the treads in you engine block.  Every ARP main stud kit exceeds the most stringent aerospace specifications.  All kits some with hardened parallel-ground washers and aerospace quality nuts.

Main Studs

The studs are manufactured from 8740 chrome moly steel alloy, precisely heat treated to 190,000 psi.  Following heat treat, each stud is centerless ground to make it as close to perfectly concentric as possible and precision J-form threads rolled after heat treat which gives them about 1000% better fatigue strength than those studs that are not.

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Cylinder Head Bolts

Main Bolts

Flywheel/Flexplate Bolts

Note:  12 point head design and larger than stock shank diameter for  increased strength and improved flywheel register, 190,000 psi rating.

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