Reinforced ARP cylinder head studs Toyota G16E-GTS

The engines concerned

The G16E-GTS is Toyota's 1.6-litre, 12-valve turbocharged three-cylinder engine (1,618 cm³), fitted to the GR Yaris, the GR Corolla and the Lexus LBX Morizo RR. ARP offers a single stud kit for it, the 403-4302, in CA625+.

As standard, the G16E-GTS cylinder head is secured by head bolts, which this kit replaces.

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.

For this three-cylinder the ARP catalogue lists the 403-4302 kit, in CA625+. 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. As an estimate, this CA625+ kit suits tuned G16E-GTS engines beyond the original output.

Technical specifications

Tightening torque

Technical guide

When assembling, the threads and the nut bearing faces receive ARP Ultra-Torque lubricant rather than engine oil. The torque and tightening sequence are to be read in the instruction sheet supplied with the kit.

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
Engine block threads	Stressed at every tightening	Preserved: the stud stays in place

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:

• Tuned G16E-GTS in a GR Yaris or GR Corolla: boost raised beyond stock
• 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

Why is it the most cost-effective solution?

On a tuned G16E-GTS, the original head fasteners limit the pressure the gasket can hold. CA625+ studs push that limit back, for an outlay that bears no relation to reopening a turbocharged three-cylinder.

Consider a reinforced head gasket

To get the most out of reinforced fasteners, pair them with a head gasket that withstands the same pressure. Here is the gasket we offer for this engine: