Reinforced ARP cylinder head bolts and studs Ford JTJA JTJB JQDA JQDB YUDA

The engines concerned

The JTJA, JTJB, JQDA, JQDB and YUDA are the variants of Ford's 1.6-litre turbocharged EcoBoost four-cylinder (1,596 cc, bore 79 mm, stroke 81.4 mm, sixteen valves), fitted to the Fiesta ST, the Focus III and the C-Max II. ARP offers two ARP2000 kits for it: the 251-4302 stud kit and the 251-3702 bolt kit.

Originally, the cylinder head is held by head bolts, which either of these ARP kits replaces.

Reinforced ARP cylinder head bolts and 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.

The 251-4302 stud kit has M10 studs with 12-point nuts, while the 251-3702 bolt kit replaces the original bolts with 12-point head bolts, no nuts. ARP2000 is an ARP proprietary alloy, heat treated to reach 220,000 psi tensile strength, with threads rolled after heat treatment. Standard engine fasteners mostly belong to property classes 10.9 and 12.9 (150,800 to 176,900 psi minimum): ARP2000 therefore offers 24 to 46 % more margin. As an estimate, the M10 ARP2000 studs hold up to 600 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

Technical guide

When assembling, the threads and the bearing surfaces under the nuts and under the bolt heads receive ARP Ultra-Torque lubricant rather than engine oil. The torque and tightening sequence of each kit are to be read in the instruction sheet supplied 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	Reinforced ARP bolts
Fastener	Original head bolt	Stud and 12-point nut	12-point head bolt
Engine block threads	Stressed at every tightening	Preserved: the stud is screwed in by hand	Stressed at every tightening

When to upgrade the cylinder head fasteners

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

• JTJA, JTJB, JQDA, JQDB or YUDA, tuned: boost pressure raised on a 1.6-litre EcoBoost
• 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

Why is it the most cost-effective solution?

On a 1.6-litre EcoBoost run at a higher boost pressure, the original head fasteners limit what the gasket can hold. An ARP2000 kit, in studs or bolts, moves that limit for an outlay far below that of reopening a Fiesta ST or Focus engine after a failed head gasket.