Reinforced ARP cylinder head studs AUDI 2.2 20V 3B AAN ABY ADU

The engines concerned

Audi's 2.2-litre 20-valve turbocharged in-line five-cylinder (2,226 cc, 81 mm bore, 86.4 mm stroke) powers the Audi S2 (3B code at 220 hp, then ABY at 230 hp), the S4 C4 (AAN code, 230 hp) and the Audi RS2 (ADU code, 315 hp).

Originally, the 2.2 20V head is held by single-use bolts of at least class 10.9, tightened cold to 40 Nm, then 60 Nm, then in two 90° stages. ARP replaces them with two 7/16 inch stud kits in 8740.

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.

Two ARP part numbers are offered: the 204-4207 and the 204-4704, the latter in the « undercut » version according to the 2026 ARP list. Their instruction sheets prescribe the same method: three equal stages up to 80 ft-lb, with lubricated washers. Material of the fasteners: 8740, a chrome-molybdenum steel that ARP specifies at 200,000 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 7/16 in, the 8740 studs hold up to 700 hp on this five-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

For both kits: the studs are screwed into the block by hand, without torque. Their instruction sheet allows thread locker if they are to be fixed permanently, on the sole condition that tightening is finished before it sets.

Both sheets add that a stud running through into the water jacket takes ARP thread sealer on its block-side threads.

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.

These values come from ARP instruction sheets 204-4207 and 204-4704; the current official sheet remains the reference, with the full procedure and the manufacturer's tightening order. Read the ARP 204-4207 instruction sheet ; Read the ARP 204-4704 instruction sheet

Technical guide

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

ARP undercut studs

An undercut stud has a reduced-diameter shank. This profile, ARP explains, spreads stretch more evenly across the studs: the cylinder head is clamped with a steadier force, gasket compression is better compensated and the gasket is less likely to fail.

The ARP brand

Founded in the early 1970s by Gary Holzapfel, who came from the aerospace industry, ARP (Automotive Racing Products) set itself the mission of eliminating engine failures caused by inadequate fasteners in competition. Its thousands of parts are designed and produced in California, in several material grades depending on the application.

Advantages over the original bolts

Criterion	Original head bolts	Reinforced ARP studs
Tightening method	Torque then angle (40 Nm, 60 Nm, then +90° +90°)	Torque only, in 3 stages
Block threads	Stressed at every tightening	Preserved (studs fitted hand tight)

When studs become necessary

The original fasteners are sized for the engine as it leaves the factory. They need to be reinforced when:

• 3B, ABY, AAN or ADU with raised turbo boost or a larger turbo
• The compression ratio rises as the build progresses
• The original gasket is replaced by a reinforced MLS gasket, which requires a high and uniform preload
• The engine has already suffered a lifted head or a gasket leak
• Competition use imposes severe heat cycles and regular head removals

Vehicle compatibility

Why is it the most cost-effective solution?

On a turbocharged five-cylinder whose boost keeps climbing, the original single-use bolts relax and leave the head gasket to take the load. ARP studs in 8740 fitted hand tight hold the head down harder: less risk of a blown gasket, and of a rebuild costing far more than the kit.

Consider a reinforced head gasket

To get the most out of reinforced fasteners, pair them with a head gasket that withstands the same pressure. Here is the gasket we offer for this engine: