Reinforced ARP main studs for Ford EcoBoost 2.3

The Ford engine concerned

This kit is designed for the 2.3-litre Ford EcoBoost four-cylinder, 16 valves, turbocharged with direct injection, found in the Focus RS (Mk3) and Focus ST (Mk4), the Mustang (S550), the Ranger, the Explorer and the Bronco.

Reinforced ARP studs for main bearings

Each main bearing takes a share of the loads the connecting rods pass on at every combustion. Pulled downwards, the main cap tends to slide on its parting line: over time the mating faces brinell and the bearing bore loses its shape.

The ARP2000 studs in this kit, in M10 x 1.25, replace the original main cap fasteners of the 2.3-litre EcoBoost. Once the block threads are cleaned, they are screwed in by hand, with no torque applied. The washers are degreased on both sides, then fitted with the stamped face against the cap. Threads and nut undersides receive ARP Ultra-Torque lubricant, and the ten nuts are tightened with a 16 mm socket in three rising passes, in the manufacturer's order: 33, 67 then 94 Nm. Only the nut turns, which gives a preload truer to the torque read.

These fasteners are made from ARP2000, an ARP-specific alloy steel that reaches 220,000 psi tensile strength after heat treatment; the threads are rolled afterwards. Compared with classes 10.9 and 12.9 of the original fasteners, from 150,800 to 176,900 psi minimum tensile strength, the margin ranges from 24 to 46%. The ARP2000 studs in M10 x 1.25 hold up to 1,100 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

Each stud goes into the block screwed in by hand, with no torque at all. The instruction sheet for this kit mentions no thread locker.

The nuts are tightened in the sequence the manufacturer specifies for the main caps; the instruction sheet supplied with the kit describes the full procedure.

Values taken from the ARP 151-5407 instruction sheet in force at the date of publication; the official instruction sheet prevails should any difference appear. Read the ARP 151-5407 instruction sheet

Technical guide

The torque figures given only apply with ARP assembly grease, never with engine oil.

The ARP brand

ARP, short for Automotive Racing Products, was born in the early 1970s on the initiative of Gary Holzapfel, an engineer from the aerospace sector, in response to the engine failures caused in racing by inadequate fasteners. Today the brand produces thousands of part numbers in California, offered in several materials depending on the application.

Advantages over the original bolts

Criterion	Original main bolts	ARP studs
Tightening	Bolt screwed into the block, turning under torque	Nut alone turns, tightened in three passes
Block thread	Takes the rotation of the bolt at each assembly	Stud placed by hand, no effort
Positioning the caps	Cap to be held while screwing	Cap guided by the studs

When studs become necessary

• 2.3-litre EcoBoost remapped or running higher boost pressure
• Focus RS or Mustang aiming for more than 400 hp
• Bottom end opened for a rebuild
• Main caps that shift or tired block threads
• Repeated sporting driving, track, rally or drag

Vehicle compatibility

Why is it the most cost-effective solution?

The 2.3-litre EcoBoost, already turbocharged from the factory, gains power quickly with a simple remap, and its main caps then take more than the standard fasteners were designed for. These ARP2000 studs offer a comfortable preload margin for a price out of all proportion to that of a bottom end to replace.