Reinforced ARP cylinder head studs Nissan VG30DE VG30DETT

The engines concerned

The VG30DE and VG30DETT are Nissan's 3.0-litre 24-valve double overhead camshaft V6 engines (2,960 cc in the NGK catalogue), the VG30DETT being the Twin Turbo version. The VG30DE powers the naturally aspirated 300ZX, the Cedric, Gloria and Cima and the Maxima among others, the VG30DETT the 300ZX Twin Turbo (Z32). ARP matches both engines to its 202-4308 stud kit, with 12-point nuts.

As built, the cylinder head of the VG30DE and VG30DETT is secured by the standard fasteners; the studs of ARP kit 202-4308 replace them, with their nuts.

Reinforced ARP cylinder head studs

The job of the head fasteners is to keep the cylinder head locked to the block despite the pressure inside the combustion chambers. They keep the gasket compressed; as soon as their clamping force drops, leaks appear between head and block.

ARP kit 202-4308, in 8740, goes into an M12 x 1.75 block thread according to the sheet. According to it, the studs are first run in by hand only; the head is then fitted, and ARP Ultra-Torque goes on threads, nuts and washers before torque tightening in three equal passes. Material of the fasteners: 8740, a chrome-molybdenum steel that ARP specifies at 190,000 psi tensile strength. Factory-fitted fasteners usually fall into classes 10.9 and 12.9, with 150,800 to 176,900 psi minimum tensile strength. In M12 x 1.75, the 8740 studs hold up to 1,000 hp on this six-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

No torque is applied to the studs as they go into the block: they are screwed in by hand. The instruction sheet leaves the option of thread locker to mount them permanently, provided tightening is done before the product hardens.

Before fitting, all block threads are cleaned, then run through again if needed with the ARP 912-0008 thread chaser (M12 x 1.75).

If a stud ends in the water jacket, its block-side threads are lubricated with ARP Thread Sealer.

Follow the tightening sequence recommended by the manufacturer and bring to torque in three stages; the stated values assume ARP lubricant on the threads and under the nuts.

According to the instruction sheet, ARP lubricant is also applied to the washers, as on the threads.

Source of these values: ARP instruction sheet 202-4308, revision current at the time of publication. The official instruction sheet applies if any discrepancy appears; it covers the entire procedure and the tightening sequence. Read the ARP 202-4308 instruction sheet

Technical guide

All torque values on this page are given with ARP assembly grease on the threads and under the nuts; another lubricant would make them wrong.

The ARP brand

Gary Holzapfel, a former aerospace engineer, created ARP (Automotive Racing Products) in the early 1970s to tackle engine failures caused by insufficiently strong fasteners in racing. Today the brand develops and manufactures thousands of parts in California, available in several material grades as needed.

Advantages over the original bolts

Criterion	Original head bolts	Reinforced ARP studs
Block threads	Stressed at every tightening	Preserved: studs fitted by hand

When studs become necessary

Standard fasteners remain suitable as long as the engine keeps its original combustion pressure. They reach their limits in the following cases:

• VG30DETT Twin Turbo pushed, or VG30DE boosted: cylinder pressure beyond stock
• Compression ratio raised for more power
• Reinforced MLS head gasket, which requires a high and even preload
• Cylinder head that has already lifted or gasket that has already leaked
• Racing or track use, with repeated heat-ups and frequent teardowns

Vehicle compatibility

Why is it the most cost-effective solution?

On a tuned VG30 V6, it is the standard fasteners that limit how well the gasket holds. M12 8740 studs keep their preload at much higher pressures, for a budget out of all proportion to rebuilding two cylinder heads.