Saving the Bottom End: Billet Caps for Gen III Hemis and Oversized Studs for Stripped LS Blocks

Two of the most common platforms in American performance share a bottom-end weak spot, just in different ways. The Gen III Hemi's main caps are held by only two vertical bolts. The LS block, after years of rebuilds and boost, often has threads that are simply worn out. Both problems send otherwise good blocks to the scrap pile. Two recent products aim to keep them out of it.

EngineLabs detailed Livernois Motorsports' billet main caps for the Hemi, and LSX Magazine covered ARP's new Block Saver stud kits for LS engines. Neither is glamorous. Both are the kind of parts that decide whether a big-power engine lives.

The Hemi's two-bolt problem

Unlike many modern designs, the Gen III Hemi block does not use four vertical main fasteners. EngineLabs explains it uses two per cap, along with two cross bolts in the block skirt. Even the robust BGE, or Big Gas Engine, block uses that arrangement, and that leaves room for improvement when boost and cylinder pressure climb.

Livernois's fix starts with material. Its caps are machined from solid 1044 steel plate, a medium-carbon steel used in heavy-duty mechanical parts, which EngineLabs says is significantly stronger than the OEM powdered-metal caps. Livernois also slightly reshaped the caps to better resist extreme loads, while keeping clearance for the oil pan and for OEM and aftermarket windage trays.

The kit includes billet replacements for all five main caps and fits the full lineup of OEM Gen III Hemi blocks: 5.7, 6.1, 6.2 and 6.4 liters.

ARP hardware holds it together

Caps are only as good as what clamps them. Livernois pairs its caps with ARP's 8740 chromoly main stud kit, using 12 mm main studs and 8 mm 8740 side bolts. EngineLabs lists a 190,000 psi tensile strength for both, well above the OEM bolts, with a 100 lb-ft torque spec on the studs. Because the Hemi has only two vertical fasteners per cap, the stronger side bolts carry extra importance.

Clamp load is the reason studs matter as much as the caps. A main cap that moves under load wears its bearing and can walk the crank out of alignment, and the two-vertical-bolt Hemi design gives that movement fewer fasteners to fight. Pairing a stiffer cap with fasteners rated well above stock attacks the problem from both sides.

The LS problem: pulled threads

The LS is famously tough, but its blocks have been rebuilt, boosted and swapped for more than two decades now. LSX Magazine describes the familiar teardown surprise: head bolt holes or main cap threads too damaged to trust, and a block headed for the scrap pile.

ARP's Block Saver kits for Gen III and Gen IV LS engines solve that with a stepped stud. The block end has an oversized 1/2-13 thread, so the damaged hole can be machined and tapped larger into fresh material. The top keeps the standard 7/16-20 thread, so the nut side stays the same as any LS head stud setup.

ARP offers the head stud kit in two materials. One uses its proprietary ARP2000 alloy, nominally rated at 220,000 psi tensile strength. A new kit, part number 434-4348, uses Custom Age 625+ studs rated at 260,000 to 280,000 psi, aimed at high-horsepower and boosted engines where clamping force is critical. ARP also offers a main stud repair kit for aluminum RHS blocks, part number 234-5803, in ARP2000.

How ARP makes them

Like ARP's other studs, these are centerless ground for concentricity, and the threads are rolled after heat treatment rather than cut. ARP says that process can provide up to 20 times the fatigue life of ordinary studs, LSX Magazine reports. The company lists more than 5,500 applications in its catalog.

ARP's latest catalog lists the repair kits alongside the rest of its range, and LSX Magazine notes the company's technical department can help with fitment questions, which is worth using before a block goes to the machine shop for oversized tapping.

Not a substitute for machine work

Both fixes depend on a machinist. LSX Magazine is clear that a damaged LS block still has to be inspected and properly machined before oversized studs go in, and billet main caps on any block mean line-boring and careful fitting. These are not bolt-on parts in the driveway sense.

What they do is change the math on a block. A Hemi that would have been a weak link at high boost can carry steel caps and better studs. An LS block with pulled threads, maybe the last of a casting someone wanted to keep, gets another life. In a hobby built on finding, fixing and reusing hard parts, that is worth a lot.