Reinforced ARP cylinder head studs Toyota 2JZ-GE 2JZ-GTE 1JZ-GTE

The engines concerned

The 2JZ-GE and 2JZ-GTE are Toyota's 3.0-litre, 24-valve inline six-cylinder engines (2,997 cm³, 86 mm bore and stroke): the first is naturally aspirated, the second turbocharged. The 2JZ-GTE powers the Supra (JZA80) and the 2JZ-GE the Lexus GS300 (JZS147). The 1JZ-GTE, a 2.5-litre turbocharged inline six (2,492 cm³, 86 mm bore, 71.5 mm stroke), is part of the application list of kit 203-4702.

As standard, the 2JZ-GE and 2JZ-GTE cylinder head is secured by 14 head bolts (Toyota part number 90910-02102), tightened to 34 Nm and then through two 90° stages.

Reinforced ARP cylinder head studs

Cylinder head fasteners work constantly: they hold the head tight against the block, crush the gasket to the right value and hold back the push of the gases at every combustion. If they lose even a little tension, the gasket starts to leak.

Three ARP stud kits with 12-point nuts are offered: 203-4205 and its undercut version 203-4702, in 8740 and 7/16", plus 203-4301 in CA625+ and M11 x 1.25. The studs are screwed into the block by hand, the cylinder head and gasket are fitted next, then the nuts are torqued, which gives a higher preload. In 7/16", the 8740 studs hold up to 900 hp on this six-cylinder engine (calculated estimate). On this six-cylinder engine, the limit of the CA625+ studs in M11 x 1.25 lies at 1,100 hp (calculated estimate).

Technical specifications

Tightening torque

For all three kits: no torque is applied to the studs as they go into the block: they are screwed in by hand. The instruction sheet leaves the option of thread locker to mount them permanently, provided tightening is done before the product hardens.

If the studs open into a water jacket, the instruction sheets call for an ARP sealant on their threads.

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.

The torque figures above come from ARP instruction sheets 203-4205, 203-4702 and 203-4301; only the official sheet in force applies, including for the full procedure and the tightening sequence. Read the ARP 203-4205 instruction sheet; Read the ARP 203-4702 instruction sheet; Read the ARP 203-4301 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 available grades

ARP undercut studs

An undercut stud has a reduced-diameter shank. This profile, ARP explains, spreads stretch more evenly across the studs: the cylinder head is clamped with a steadier force, gasket compression is better compensated and the gasket is less likely to fail.

The ARP brand

Gary Holzapfel, a former aerospace engineer, created ARP (Automotive Racing Products) in the early 1970s to tackle engine failures caused by insufficiently strong fasteners in racing. Today the brand develops and manufactures thousands of parts in California, available in several material grades as needed.

Advantages over the original bolts

Criterion	Original head bolts	Reinforced ARP studs
Tightening method	Torque then angle (2JZ: 34 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:

• 2JZ-GE: higher boost pressure, or a turbo 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: 90910-02102

Why is it the most cost-effective solution?

The original head fasteners do not last long once power climbs sharply. Reinforced fasteners in 8740 or CA625+ withstand a much higher combustion pressure: the risk of a failed gasket or a broken bolt drops, and with it the risk of an expensive engine rebuild.

Consider a reinforced head gasket

Reinforced fasteners are only fully worthwhile with a head gasket able to resist the same pressure. We offer the following part for this engine: