Reinforced ARP cylinder head studs FORD MAZDA L3-VE L3-VDT

The engines concerned

Mazda's 16-valve 2.3-litre four-cylinder (MZR), listed by ARP as the Duratec 2.3 for Ford, comes in two versions. The L3-VE, a naturally aspirated 2,261 cc, powers the Mazda 3 (BK), Mazda 6 Estate (GY) and MPV III, as well as the Ford Escape (R1) sold in Asia and Oceania. The L3-VDT, its turbocharged version with an 87.5 mm bore and a 94 mm stroke, powers the Mazda 3 MPS, Mazda 6 MPS and CX-7.

As standard, on the L3-VDT, the cylinder head is held down by cylinder head bolts (Mazda part L3K9-10-135A, set of 10, single use), tightened in five steps according to the 2010 Mazdaspeed3 workshop manual: 3 to 11 Nm, 13 to 17 Nm, 43 to 47 Nm, then twice 88 to 92°. The ARP studs replace these bolts.

Reinforced ARP cylinder head studs

Every combustion cycle pushes the cylinder head upwards. The head fasteners resist it by keeping a constant clamping pressure on the gasket; if that pressure drops, the seal is no longer guaranteed.

Two ARP part numbers are offered: the 151-4204, listed by ARP for Ford's Duratec 2.3, and the 218-4702, listed for Mazda's MZR 2.3, both in 8740 and 10 mm in diameter. According to the instruction sheets, the studs are screwed into the block by hand before the head is fitted; the nuts are then tightened in three equal passes, after the threads, nuts and washers have been lubricated with ARP Ultra-Torque. ARP makes these fasteners in 8740, a chrome-molybdenum steel whose tensile strength reaches 200,000 psi. To put this figure in context, original engine fasteners generally belong to classes 10.9 and 12.9, whose minimum ranges from 150,800 to 176,900 psi. On this four-cylinder engine, the limit of the 8740 studs in M10 lies at 500 hp (calculated estimate).

Technical specifications

Tightening torque

For both kits: 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.

According to the sheets, ARP thread sealer is applied to the block-side threads where the studs open into the 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 instruction sheet also calls for ARP lubricant on the washers.

This torque value comes from ARP instruction sheets 151-4204 and 218-4702; the official sheet in force prevails for the whole procedure, including the manufacturer's tightening order. Read the ARP 151-4204 instruction sheet; Read the ARP 218-4702 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 (L3-VDT: 3 to 11, 13 to 17, 43 to 47 Nm, then twice 88 to 92°)	Torque only, in 3 passes
Block threads	Stressed at every tightening	Spared by hand-tight fitting

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:

• L3-VE or L3-VDT built for fast road or track use (turbo kit, modified engine map, raised boost pressure)
• 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: L3K9-10-135A

Why is it the most cost-effective solution?

A standard L3-VDT, the 260 hp turbo of the Mazda MPS models, works with a margin set for series output. As soon as boost pressure or the engine map changes, the head and the gasket are the first parts to suffer. ARP 8740 studs keep the head pressed down with a steadier clamping load; reopening an engine for a blown gasket costs far more than these kits.

Consider a reinforced head gasket

Reinforced fasteners and the head gasket work together: the gasket must hold the same pressure as the fasteners. The matching gasket for this engine: