Reinforced ARP cylinder head studs Audi AGB AZB ASJ AZR

The engines concerned

Audi's 2.7-litre twin-turbo 30-valve V6 powers the Audi S4 B5 (codes AGB and AZB, 265 hp) and RS4 B5 (codes ASJ and AZR, 380 hp). ARP offers the 204-4105 stud kit for it, in ARP2000, with 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 204-4105 kit is supplied as studs with their 12-point nuts, in M11 x 1.5 thread, in ARP2000.

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

The ARP2000 range relies on an alloy steel developed by ARP: after heat treatment it reaches 220,000 psi tensile strength, and the threads are rolled afterwards. As standard bolts generally belong to classes 10.9 and 12.9, i.e. 150,800 to 176,900 psi minimum, ARP2000 exceeds them by 24 to 46 %.

On this six-cylinder engine, the limit of the ARP2000 studs in M11 x 1.5 lies at 1,100 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 torque figures above come from ARP instruction sheet 204-4105, 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 204-4105 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	ARP2000 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 twin-turbo V6 (higher boost, remapped engine management)
• 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 twin-turbo V6 head fasteners are sized for stock power: as soon as combustion pressure rises, the gasket and the fasteners are the first to suffer. ARP2000 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.