Reinforced ARP cylinder head studs BMW S65

The BMW engine concerned

The S65B40 is BMW's V8 petrol engine of 4.0 litres (3,999 cm³, 92 mm bore, 75.2 mm stroke), with thirty-two valves. Naturally aspirated and built from 2007 to 2013, it powers the M3 E90 (saloon), E92 (coupé) and E93 (convertible), as well as the Wiesmann GT MF4 and MF4 Roadster.

As standard, the two cylinder heads are held by M10 x 1.5 bolts (part number 11 12 7 838 831), which must be replaced, washed and oiled. They are tightened to 40 Nm, then 90° and another 90°.

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 201-4307 kit contains 20 ARP2000 studs in M10 x 1.5, with their 20 nuts (12-point) and 20 washers, that is ten studs per cylinder head, plus four M6 fasteners with their washers. The instruction sheet calls for each stud to be threaded into the block by hand with the head removed, then for the head to be fitted and the nuts torqued. The block threads are thus spared. Developed by ARP, ARP2000 alloy steel is heat treated to 220,000 psi tensile strength, and its threads are rolled once the treatment is done. Compared with the 10.9 and 12.9 classes of standard fasteners, between 150,800 and 176,900 psi minimum tensile strength, the gap reaches 24 to 46 %. In M10 x 1.5, the ARP2000 studs hold up to 1,200 hp on this V8 engine (calculated estimate).

Technical specifications

Tightening torque

The studs are fitted into the block by hand, without a torque wrench. For a permanent installation, the instruction sheet accepts thread locker, with tightening to be completed before it sets.

All block threads are cleaned before fitting, using the ARP thread chasers 912-0003 (M10 x 1.5) and 912-0012 (M6 x 1.00) if necessary; if a stud opens into a water gallery, its thread is coated with ARP sealant.

The M6 fasteners of the kit (numbers 11 and 12 in the instruction sheet) are tightened to 11 ft-lb, about 15 Nm, after the M10 studs.

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.

The torque figures above come from ARP instruction sheet 201-4307, 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 201-4307 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

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	Torque, then two 90° angles (40 Nm + 90° + 90°)	Torque only, in three equal 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:

• S65B40, naturally aspirated from the factory, fitted with a supercharger or pushed beyond its stock output
• 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

OEM reference: 11 12 7 838 831

Why is it the most cost-effective solution?

As standard, the head bolts are tightened to torque then angle and stretch permanently. Stronger, the ARP2000 fasteners stand up to a much higher combustion pressure, forced induction included: they reduce the risk of gasket leaks or breakage, and therefore of a rebuild out of all proportion to the price of the kit.

Consider a reinforced head gasket

Reinforced fasteners are only fully worthwhile with a head gasket able to resist the same pressure. We offer the following part for this engine: