Does the Head Stud Kit for G16E-GTS include a head gasket?

No. The HKS Head Stud Kit for G16E-GTS contains four M12 center studs, four M11 side studs, matching 12-point flange nuts and washers, molybdenum grease and the installation manual. HKS designed the studs to seal best with its grommet type head gasket, which is sold separately.

Does the kit fit the GR Corolla and the GR Yaris?

Yes. HKS USA lists part 22999-AT001 for the 2023 to 2025 GZEA14H GR Corolla, and HKS Japan lists it for the GXPA16 GR Yaris built from September 2020 to March 2024. Both cars use the G16E-GTS, so owners of later or other models should confirm fitment first.

Why upgrade from the factory head bolts?

HKS changed the stud material so it resists elongation even under excessive boost pressure. When fasteners stretch, the head can lift under combustion pressure and the gasket starts to leak. The bottoming design also lengthens the engaged thread in the block and spreads the stress.

Is installation a home garage job?

No. HKS states that installation must be done by a professional. The work means cleaning and possibly tapping the block threads so each stud bottoms, greasing every stud, nut and washer, and torquing in stages to the HKS sequence, with an extra step for grommet type gaskets.

Is a tune needed after fitting the studs?

No, not for the studs themselves. Head studs change the clamp load on the head gasket and do not affect airflow or fueling. Builds that pair them with the HKS BCD HC-TT STEP3 Pistons and Rods or more boost do need engine management tuning.

Description

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Description

HKS Pro Head Stud Kit for G16E-GTS Toyota GR Corolla

HKS’s Pro Head Stud Kit for G16E-GTS Toyota GR Corolla replaces the cylinder head fasteners on the three-cylinder engine with ARP Custom Age 625+ studs, four M12 center studs and four M11 side studs, all of the bottoming type. HKS developed the studs to add to the sealing of its grommet type head gasket for the G16E-GTS, where combustion pressure runs high. The kit suits a build with raised boost, a bigger turbo or new internals.

Development and Testing

Each stud threads to the bottom of its hole in the block, so the engaged thread is longer and stress spreads out, allowing a higher axial force. HKS controls the correct torque from that bottomed position, and changed the stud material so the studs resist elongation even under excessive boost. Carburized washers with an enlarged seat surface resist deformation under clamp load.

Features

ARP Custom Age 625+ material chosen for tensile strength, fatigue life and corrosion resistance
Bottoming stud design with longer engaged threads in the block
Carburized black oxide washers with an enlarged seat surface
Dedicated HKS molybdenum grease for assembly, also sold separately as 22999-AK002

Specifications

Center studs: 4, M12 x 1.25
Side studs: 4, M11 x 1.25
Nuts: 8, 12-point flange
Washers: 4 M12 and 4 M11
Material: ARP Custom Age 625+
Shipping Weight: 3.7lb (1.7kg)

Applications

Toyota GR Corolla: GZEA14H | 2023-2025 | G16E-GTS
Toyota GR Yaris: GXPA16 | 2020-2024 | G16E-GTS

Notes

No head gasket is included; HKS designed the studs to seal best with its grommet type head gasket
HKS USA lists the kit for the GR Corolla, while HKS Japan lists the same part number for the GXPA16 GR Yaris built from September 2020 to March 2024; both use the G16E-GTS
Professional installation by an experienced engine builder is required
The block threads may need a thread tap correction so each stud bottoms fully
With a grommet type gasket, the HKS manual for the Head Stud Kit for G16E-GTS adds a loosen-and-retighten step at initial tightening
Head studs do not add power, and any boost or power increase they support requires engine management tuning
This part is intended for off-road or competition use where emissions laws apply, and the buyer is responsible for checking local regulations

Frequently Asked Questions

Does the Head Stud Kit for G16E-GTS include a head gasket? No. The HKS Head Stud Kit for G16E-GTS contains four M12 center studs, four M11 side studs, matching 12-point flange nuts and washers, molybdenum grease and the installation manual. HKS designed the studs to seal best with its grommet type head gasket, which is sold separately.
Does the kit fit the GR Corolla and the GR Yaris? Yes. HKS USA lists part 22999-AT001 for the 2023 to 2025 GZEA14H GR Corolla, and HKS Japan lists it for the GXPA16 GR Yaris built from September 2020 to March 2024. Both cars use the G16E-GTS, so owners of later or other models should confirm fitment first.
Why upgrade from the factory head bolts? HKS changed the stud material so it resists elongation even under excessive boost pressure. When fasteners stretch, the head can lift under combustion pressure and the gasket starts to leak. The bottoming design also lengthens the engaged thread in the block and spreads the stress.
Is installation a home garage job? No. HKS states that installation must be done by a professional. The work means cleaning and possibly tapping the block threads so each stud bottoms, greasing every stud, nut and washer, and torquing in stages to the HKS sequence, with an extra step for grommet type gaskets.
Is a tune needed after fitting the studs? No, not for the studs themselves. Head studs change the clamp load on the head gasket and do not affect airflow or fueling. Builds that pair them with the HKS BCD HC-TT STEP3 Pistons and Rods or more boost do need engine management tuning.

About HKS

HKS is a Japanese performance engineering brand founded in 1973 and headquartered in Fujinomiya, Shizuoka, with a long-standing reputation for developing high-quality aftermarket parts and motorsport-proven technology for enthusiast and professional applications. Known for innovations in turbocharging and engine performance, HKS produces a broad range of components including exhaust systems, turbo kits, electronics / engine management, and suspension solutions, with product development heavily influenced by decades of involvement in racing disciplines such as circuit time attack, drag, and drifting.

Additional Information

The Bulletproof Automotive website contains many thousands of products purchased in multiple different currencies. All of the prices are entered manually and accurately at the time of entry. Due to the consistently fluctuating international exchange rates, at times prices may not be able to be honored at their original intended rate. We apologize for any inconvenience this may cause, unfortunately our website is unable to compensate dynamically for what can at times be volatile changes in the cost of items due to currency values fluctuating, changes in prices from suppliers, changes in shipping and import duties, and other factors. Rest assured that any order you place on line will be at zero risk to you in this area. If in the event your order cannot be fulfilled at the original intended website price we will offer you a 100% refund, no questions asked. We will continue to do our best to maintain updated prices and we will always continue to offer our price match guarantees as well to ensure our prices are always the best for you. In short, prices may change without notice. It is always advised to give us a call prior to placing your order online to confirm availability and to confirm current pricing.

Shipping Policy

Items that are in stock in the US, either at Bulletproof’s warehouse or at a supplier’s warehouse, are generally delivered within 7-10 days. Special order items from overseas take considerably longer. As a courtesy Bulletproof offers delivery estimates to our customers which take into consideration manufacturer availability and shipping schedule. These estimates represent our best guess based on previous orders from the manufacturer and do not in any way imply a guaranteed delivery window. Many manufacturers work in a “just in time” inventory system and often take 2-20+ weeks to produce an item once an order is submitted. All deliverable items are then sent to our Japanese warehouse. Bulletproof ships a minimum of one full ocean freight container every month from Japan, oftentimes more than one a month. Ocean freight takes an average of 4 weeks. Typically it breaks down to one week in Japan for paperwork and customs, two weeks by boat and one week in US customs/clearance. Due to the wide number of variables between manufacturer and shipping schedules, delivery estimates are simply just that – estimates. We attempt to estimate conservatively and we usually deliver faster than our estimates suggest. It is not Bulletproof’s policy to guarantee delivery time of any special order item, this is impossible for us to do. By ordering you acknowledge that there is no required delivery ETA and an order may not be canceled or altered due to manufacturing or shipping delays, all ETA’s are provided as a best guess only. Please review the full Terms & Conditions here.

BP Pricing Difference

We do pricing a little differently on our JDM brands and we believe in making things simple and clear. No hidden fees or surcharges. Every price you see includes the shipping cost to our office in Los Angeles, California and all the associated taxes/duties/fees for bringing the products into the US. The only shipping you ever pay is from our facility in the US to your location. Be wary of resellers that don’t include the cost of international shipping in their pricing on JDM parts. While we believe we’ll always have the lowest all-in price on JDM products, we offer a price match guarantee for all authentic parts purchased from authorized dealers as well. For many international customers, it’s much more affordable to ship from the USA than from Japan directly, as the air freight and ocean freight costs are typically much less. However, for customers looking to ship directly from Japan outside of North America, or domestically in Japan, we can provide pricing specifically for that scenario. Please do not hesitate to contact us with any pricing questions or concerns. Please email us at sales@bulletproofautomotive.com with any inquiries.

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HKS Pro Head Stud Kit for G16E-GTS Toyota GR Corolla [22999-AT001]

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HKS Pro Head Stud Kit for G16E-GTS Toyota GR Corolla

Development and Testing

Features

Specifications

Applications

Notes

Frequently Asked Questions

About HKS

Reviews