Reinforced ARP cylinder head studs Volkswagen VR6 AAA ABV AES

The engine concerned

Volkswagen's 12-valve VR6, in 2.8 and 2.9 litres, is a six-cylinder with staggered cylinders in a very narrow angle, under a single cylinder head (original bore 81 mm, built from 1991 to 2004 depending on version). The codes AAA, ABV and AES identify it; it powers the Volkswagen Golf 3 VR6 and Corrado VR6, as well as the Passat, among others. ARP offers the 204-4705 stud kit for it, in 8740, with washers and 12-point nuts.

Reinforced ARP cylinder head studs

Cylinder head fasteners work constantly: they hold the head tight against the block, crush the gasket to the right value and hold back the push of the gases at every combustion. If they lose even a little tension, the gasket starts to leak.

The ARP 204-4705 kit is supplied as studs with their washers and 12-point nuts, in 7/16 in diameter, in 8740.

According to the instruction sheet, the studs are screwed into the block by hand only; the cylinder head is fitted next, then lubricated washers and nuts are tightened in three equal passes, in the manufacturer's tightening sequence.

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.

On this six-cylinder engine, the limit of the 8740 studs in 7/16 in lies at 900 hp (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.

The instruction sheet asks you to clean all the block threads, with the ARP thread chaser if needed, for proper engagement and accurate torque.

ARP thread sealer is only used if the studs open into a water jacket.

Tightening to torque is done in three steps, in the order set by the engine manufacturer, with ARP lubricant applied to the threads and under the nuts, a condition for the table values to apply.

The washers also receive ARP lubricant, as stated in the instruction sheet.

The torque figures above come from ARP instruction sheet 204-4705, revision applicable on the day the page went online. The official instruction sheet prevails in case of difference and describes the complete procedure, tightening sequence included. Read the ARP 204-4705 instruction sheet

Technical guide

The stated tightening torques only make sense with ARP assembly grease, applied to the threads and under the nuts.

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	8740 studs
Block thread	Stressed at every tightening	Spared (studs screwed in by hand)

When studs become necessary

On an engine left standard, the original fasteners do their job. Switching to reinforced fasteners becomes worthwhile as soon as:

• Power raised on a VR6 (turbo, supercharger, hard-tuned naturally aspirated build)
• The compression ratio is increased
• A reinforced MLS gasket is fitted, with its need for a high and even preload
• The head has already lifted or the gasket has already failed
• The engine is used in competition, with intense heat cycles and repeated teardowns

Vehicle compatibility

Why is it the most cost-effective solution?

The original VR6 head bolts are sized for stock power: as soon as combustion pressure rises, the gasket and the fasteners are the first to suffer. ARP 8740 studs bring a higher clamp load and keep the gasket pressed down; redoing a six-cylinder head, with gasket and labour, costs far more than the kit.