Reinforced ARP cylinder head studs MINI BMW Peugeot Citroën N12B16 N13B16 N14B16 N16B16 N18B16 EP6

The engines concerned

The N12B16, N14B16, N16B16 and N18B16 are the 1.6-litre inline four-cylinder petrol engines (1,598 cm³, 77 mm bore, 85.8 mm stroke) of the Prince family, developed jointly by BMW and PSA. The N12B16 and N16B16 power the MINI Cooper and One (R55 to R61); the turbocharged N14B16 and N18B16 power the Cooper S and the John Cooper Works. The same engines, used by PSA under the codes EP6, EP6C, EP6DT, EP6DTS and EP6CDTX, power Peugeot and Citroën models (207, 208, 308, RCZ, C3, C4, DS3, DS4); the N13B16, also listed by ARP, powers BMW 1 Series and 3 Series models.

As standard, the cylinder head is held by M10 main bolts, 145 mm long (reference 11 12 7 560 274, Torx bolt set), supplemented by M8 bolts of 95 and 35 mm. The M10 bolts are tightened to 30 Nm, then 90° and a further 90°; the M8 bolts of 95 mm to 15 Nm, then 90° and a further 90°; the M8 bolt of 35 mm to 30 Nm. This angle tightening permanently stretches the bolts: they are single-use.

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.

ARP kit 201-4304 contains 13 fasteners in ARP2000: 10 M10 studs with 12-point nuts, 2 M8 studs (no. 11 and 12) and 1 M8 bolt (no. 13). According to its instruction sheet, the studs are first hand-threaded into the block, the cylinder head is fitted next, then the nuts are torqued, which gives a higher preload. 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 %. In M10 x 1.5, the ARP2000 studs hold up to 600 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

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.

A stud that opens into a water jacket receives ARP thread sealant on its block-side threads.

After the three stages for the M10 studs no. 1 to 10, the two M8 studs no. 11 and 12 are tightened to 47 Nm, then the M8 bolt no. 13 to 34 Nm.

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.

According to the instruction sheet, ARP lubricant is also applied to the washers, as on the threads.

Source of these values: ARP instruction sheet 201-4304, revision current at the time of publication. The official instruction sheet applies if any discrepancy appears; it covers the entire procedure and the tightening sequence. Read the ARP 201-4304 instruction sheet

Technical guide

To obtain the intended preload, ARP assembly grease must be present on the threads and under the nuts: the torque figures in the table are established with it.

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 (30 Nm + 90° + 90°)	Torque only, in 3 stages
Block threads	Stressed at every tightening	Preserved (stud fitted hand tight)

When studs become necessary

Standard fasteners remain suitable as long as the engine keeps its original combustion pressure. They reach their limits in the following cases:

• Higher boost pressure on the turbocharged engine, or forced induction added to the naturally aspirated engine
• Compression ratio raised for more power
• Reinforced MLS head gasket, which requires a high and even preload
• Cylinder head that has already lifted or gasket that has already leaked
• Racing or track use, with repeated heat-ups and frequent teardowns

Vehicle compatibility

OEM reference: 11 12 7 560 274

Why is it the most cost-effective solution?

Tightening to torque then angle stretches the original head bolts for good. Reinforced, the ARP2000 fasteners cope with a much higher combustion pressure, even with a turbo: the risk of gasket leaks or breakage drops, and with it the risk of a repair 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: