Reinforced ARP cylinder head studs Toyota 3S-GE 3S-GTE

The engines concerned

The 3S-GTE is Toyota's 2.0-litre, 16-valve turbocharged inline four-cylinder (1,998 cm³, 86 mm bore and stroke), built from 1986 to 2007 alongside its naturally aspirated counterpart, the 3S-GE. The 3S-GTE powers the Celica GT-Four and the MR2 Turbo, among others. ARP lists the 3S-GE, 3S-GTE and 3S-GE BEAMS for kit 203-4204, and the 3S-GTE alone for kit 203-4207.

According to our manufacturer data, the original 3S-GTE head fasteners are tightened to torque and then through an angle.

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 stud kits with nuts are offered for these engines: the 203-4204, in 8740 with a 10 mm thread, and the 203-4207, in CA625+ with an M10 x 1.25 thread.

According to the instruction sheets, the studs are screwed into the block by hand first; the cylinder head is fitted afterwards, then washers and nuts are tightened to torque in the manufacturer's order.

ARP makes these fasteners in 8740, a chrome-molybdenum steel whose tensile strength reaches 190,000 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.

CA625+ (Custom Age 625+) is a super-alloy that ARP rates at a typical tensile strength of 260,000 to 280,000 psi, with long fatigue life and high toughness. It is fully resistant to atmospheric corrosion and oxidation, and ARP states it is immune to both hydrogen embrittlement and stress corrosion. As a reference point, standard engine fasteners mostly belong to property classes 10.9 and 12.9, i.e. a minimum tensile strength of 150,800 to 176,900 psi.

These 8740 studs in 10 mm are calculated to handle up to 500 hp on this four-cylinder engine (calculated estimate). In M10 x 1.25, the CA625+ studs hold up to 600 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

For both 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.

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 also receive ARP lubricant, as stated in the instruction sheet.

The torque figures above come from ARP instruction sheets 203-4204 and 203-4207; only the official sheet in force applies, including for the full procedure and the tightening sequence. Read the ARP 203-4204 instruction sheet ; Read the ARP 203-4207 instruction sheet

Technical guide

All torque values on this page are given with ARP assembly grease on the threads and under the nuts; another lubricant would make them wrong.

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	8740 studs	CA625+ studs
Tightening method	Torque then angle (3S-GTE)	Torque only, in 3 stages	Torque only, in 3 stages
Block threads	Stressed at every tightening	Preserved (studs fitted hand tight)	Preserved (studs fitted hand tight)

When studs become necessary

The original fasteners are sized for the engine as it leaves the factory. They need to be reinforced when:

• Higher boost pressure on the 3S-GTE, or a turbo added to a naturally aspirated 3S-GE
• The compression ratio rises as the build progresses
• The original gasket is replaced by a reinforced MLS gasket, which requires a high and uniform preload
• The engine has already suffered a lifted head or a gasket leak
• Competition use imposes severe heat cycles and regular head removals

Vehicle compatibility

Why is it the most cost-effective solution?

The original head fasteners are sized for stock power: as soon as combustion pressure rises, the gasket and the fasteners are the first to suffer. Reinforced in 8740 or CA625+, ARP fasteners withstand a clearly higher pressure; the risk of a failed gasket or a broken bolt drops, and with it the risk of a repair costing far more than the kit.