Reinforced ARP cylinder head studs BMW WIESMANN S63

The engine concerned

The S63B44 is BMW's 4.4-litre twin-turbo petrol V8 (4,395 cm³, 89 mm bore, 88.3 mm stroke), in production since the late 2000s. It powers the M5 (F10, then F90), the M6 and M8, the X5 M and X6 M, and the Wiesmann MF5.

As standard, each cylinder head is held by a set of M11 x 1.5 bolts, 175 mm long (part number 11 12 7 607 557).

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.

Two ARP stud kits with 12-point nuts, M11 diameter, are offered: the 201-4702 in ARP2000 and the 201-4703 in CA625+. According to the instruction sheets, the cylinder head and gasket are installed first, and the studs are then screwed into the block. In M11, the ARP2000 studs hold up to 1,400 hp on this V8 engine (calculated estimate). On this V8 engine, the limit of the CA625+ studs in M11 lies at 1,700 hp (calculated estimate).

Technical specifications

Tightening torque

For both kits: no torque when screwing the studs into the block: hand tight is enough. The instruction sheet says nothing about thread locker; ARP mentions that some engine builders use a blue product on the block end, excluding the nuts and any mixing with its assembly grease, with tightening to be completed before the product sets.

Final tightening is done in three successive stages, following the manufacturer's tightening sequence; these torque figures only hold with ARP assembly lubricant on the threads and under the nuts.

No trace of oil under the washers: they are fitted dry, wiped on both sides, and the head seats are degreased for even tightening.

The torque figures shown come from ARP instruction sheets 201-4702 and 201-4703, in the revision in force on the day the page went online. Should any difference appear, the official sheet prevails; it also details the whole procedure and the tightening sequence. Read the ARP 201-4702 instruction sheet; Read the ARP 201-4703 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 available grades

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

ARP (Automotive Racing Products) was born in the early 1970s from the initiative of Gary Holzapfel, an engineer from the aerospace industry, determined to eliminate engine failures caused by weak fasteners in motorsport. The company designs and manufactures thousands of parts in California, in several material grades suited to each use.

Advantages over the original bolts

Criterion	Original head bolts	Reinforced ARP studs
Block threads	Stressed at every tightening	Preserved (studs fitted in the block, tightening on the nut)
Tightening	On the bolt head	On the 12-point nut, in three stages

When studs become necessary

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

• S63B44 with raised boost, through a remap or replacement of its turbochargers
• 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

OEM reference: 11 12 7 607 557

Why is it the most cost-effective solution?

The original head bolts are sized for a production engine. Stronger, ARP fasteners in ARP2000 or CA625+ cope with a far higher combustion pressure, turbos included: the gasket holds better and the risk of breakage recedes, sparing you a repair costing much more than 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: