A look at ARP head studs and what makes them bet­ter than stock

Ultimate Diesel Builder's Guide - - Contents - Text: UDBG Staff Pho­tog­ra­phy: UDBG Staff & cour­tesy of ARP (Lead cour­tesy of NADM)

The first step to cre­at­ing a suc­cess­ful busi­ness is to iden­tify a pub­lic need. Then, you’ve got to fill it.

That’s ex­actly what rac­ing en­thu­si­ast Gary Holzapfel did back in 1968 when he no­ticed friends and fel­low rac­ers suc­cumb­ing to bolt-in­duced en­gine fail­ure: He put his back­ground in fastener man­u­fac­tur­ing to use and de­vel­oped a so­lu­tion. Soon, Holzapfel be­gan mak­ing race-qual­ity fasteners with aerospace tech­nol­ogy, and ARP was born.


All of ARP fastener man­u­fac­tur­ing is done in-house at a South­ern Cal­i­for­nia fa­cil­ity. The process starts with wire coils and ends with fasteners, nuts and bolts that are su­pe­rior to what is widely con­sid­ered air­craft qual­ity. ARP’S fasteners are built to with­stand se­ri­ous rac­ing, have higher ten­sile strengths and can sur­vive higher stresses than most air­craft fasteners will ever see.


The process is sim­ple, but more pre­cise than those used for the bolts you’d find at the hard­ware or air­craft sur­plus store. First, ARP works with their steel sup­pli­ers to get the best grades of steel. While steel es­sen­tially comes in four grades, ARP uses only the top two (air­craft grade steel is gen­er­ally only a tier-two ma­te­rial—not up to ARP’S stan­dards). The orig­i­nal line, still pro­duced, is the ARP2000 line, and it ex­hibits a whop­ping 220,000psi ten­sile strength. But that isn’t even the peak strength of ARP prod­ucts. The new­est ad­di­tion to the lineup, ARP’S Cus­tom Age 625+ hard­ware, boasts an even-higher ten­sile strength of 260,000 psi—when your boost num­bers are climb­ing, these head studs are a must!

When the steel ar­rives, it’s a coil of raw steel wire and looks like a round bar. This steel wire then un­der­goes one of two pro­cesses: cold or hot head­ing. Con­trary to the name’s im­pli­ca­tion, cold head­ing is done at room tem­per­a­ture; mean­while, hot head­ing is a tad more lit­eral. (It’s not some an­gry guy yelling at the parts as they wiz down the line!) In­stead, the steel is heated to a glow­ing state to fa­cil­i­tate the form­ing of com­plex shapes and/ or tougher-than-av­er­age (for ARP) al­loys. This is just one of the many steps it takes to pro­duce the studs, nuts and bolts that will keep your race en­gine alive—even un­der the most ex­treme con­di­tions.

Af­ter form­ing the ba­sic bolt, stud or nut, with threads, heads and body di­am­e­ters to

suit the ap­pli­ca­tion, the stock is sent to ARP’S in-house heat-treat fa­cil­ity and then to shot peen­ing. Heat-treat­ing gives the bolts strength with­out brit­tle­ness, while shot peen­ing fur­ther im­proves the strength and dura­bil­ity.

All ARP prod­ucts are then ran­dom batch tested for qual­ity. Once they’ve passed the grade, they’re pack­aged up and shipped out to motorsport en­thu­si­asts around the world.

Yes, the race goes on—of­ten be­cause ARP helped keep the heads on and the rods spin­ning. UDBG

Each batch of ARP bolts is put through rig­or­ous test­ing be­fore be­ing pack­aged for ship­ping. This In­stron unit pulls the bolts apart and then reg­is­ters the force needed to make them yield and break. Bolt stretch and other fac­tors are checked here to en­sure your bolts are per­fect for your high-power needs.

Here you can see a coil feed­ing into a cold header ma­chine. No ad­di­tional heat is used in this process.

The cold head­ing process takes coil wire (L) and forms it into a ba­sic bolt head (R). Four sta­tions are needed to get the coil wire into the nec­es­sary form for the bolt mak­ing process.

Bolts are sent to the heat-treat ovens to get the cor­rect hard­ness— not too soft and not too brit­tle. This Beaver­matic is a hot­tie and turns soft steel into hard nuts and bolts.

Hot head­ing in­volves heat­ing the steel blanks to a pre­cise, red-hot tem­per­a­ture and then ap­ply­ing tons of pres­sure to form the heads. This process is used for more com­pli­cated bolt head de­signs.

ARP re­cently in­tro­duced their 625+ line of fasteners. Here you see a com­par­i­son of their ARP2000 and 625+ head stud kits for the Ford 6.0L. The 625+ studs are the shiny ones. How­ever, the dif­fer­ence goes deeper than just the look: The ARP2000 parts are made from chrome-moly steel and have an im­pres­sive ten­sile strength of 220,000 psi. The Cus­tom Age 625+ parts take it to the next level. They are made from a heat-treat­able stain­less steel and are rated at a min­i­mum ten­sile strength of 260,00 psi, with higher num­bers of­ten seen in test­ing. If you’re go­ing for Max Race power, the added clamp­ing load the 625+ can pro­vide is per­fect. For more mild builds, the ARP2000 line is bet­ter than stock and more cost ef­fec­tive.

Here you see an ARP head stud kit be­ing in­stalled on a Ford 7.3L diesel.

ARP is con­stantly devel­op­ing new prod­ucts. We found this Cat I6 en­gine in their R&D shop be­ing used to engi­neer another line of diesel en­gine up­grade assem­bly hard­ware.

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