Reinforced ARP cylinder head studs Ford 3.5 EcoBoost 3.7 Cyclone

The engines concerned

This model covers two 24-valve Ford V6 engines of the same family: the 3.5 EcoBoost, boosted (3,496 cc, bore 92.5 mm, stroke 86.7 mm), and the naturally aspirated 3.7 Cyclone. The 3.5 EcoBoost powers the Ford Explorer, Flex and GT, among others; the 3.7 Cyclone, the Ford Mustang, Explorer and Taurus. ARP gives its 153-4303 kit for the 3.5 EcoBoost and also lists it for the 3.7 Cyclone.

As built, each cylinder head is held by angle-tightened, single-use bolts (Ford part HL3Z-6065-A for the 3.5 EcoBoost). The ARP studs replace these bolts on both cylinder heads of the V6.

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.

According to the instruction sheet, the gasket and then the head are fitted first; the studs are then screwed into the block by hand, without torque (the hex socket at the end is only for fitting and removal), followed by the washers and the 12-point nuts, run down by hand after lubrication. 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 M11 x 1.5, the ARP2000 studs hold up to 1,000 hp on this V6 engine (calculated estimate).

Technical specifications

Tightening torque

The studs are fitted by hand into the block threads, without a torque wrench. The instruction sheet makes no provision for thread locker. According to ARP, some installers apply a blue one to the block-end thread only; never on the nuts or together with ARP grease, and tightening must be completed before it sets.

The instruction sheet mentions the ARP thread chaser 912-0005 (M11 x 1.5) to chase the block threads if needed, and asks for the washer seats on the head to be cleaned with solvent or brake cleaner.

The washers go on with the stamped face toward the head, which stops them turning during tightening.

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.

The washers go on dry, clean on both faces, onto degreased cylinder head seats; an oil film at this point would distort the tightening.

The torque figures above come from ARP instruction sheet 153-4303, 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 153-4303 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

On an undercut stud, ARP reduces the shank between the two threads. The studs then stretch more evenly from one to the next: the clamping force becomes more consistent and compensates for head gasket compression at installation, which reduces the risk of a blown gasket.

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 screwed in by hand)
Tightening	Angle-tightened, single-use bolts	Three stages up to the torque in the instruction sheet

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:

• EcoBoost or Cyclone V6 with output beyond stock (remap, bigger turbos, added boost)
• 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: HL3Z-6065-A (3.5 EcoBoost)

Why is it the most cost-effective solution?

An EcoBoost V6 fitted from the factory with single-use angle-tightened bolts is calibrated for stock output. Once a build has raised combustion pressure, gasket retention becomes the first weak point. ARP2000 studs hold each head with a more even clamp load; opening a V6 and its two heads again costs far more than this kit.