Why Upgrade to ARP Head Studs on a Subaru WRX?

The factory head bolts on a Subaru WRX are designed for stock power levels and normal driving conditions. Once you start increasing boost pressure, adding a larger turbo, or running higher cylinder pressures, the clamping force of factory bolts can become insufficient. This leads to head gasket lift—a condition where the cylinder head lifts slightly under combustion pressure, allowing coolant and exhaust gases to mix. ARP head studs are the go-to solution for preventing this failure. Made from high-tensile materials like 8740 chromoly steel, they provide a much higher and more consistent clamping load than OEM bolts.

For any WRX owner planning to push beyond stage 2 power levels, upgrading to ARP studs is a critical reliability improvement.

Unlike bolts, which are torqued into the block, studs are threaded into the block and then nuts are torqued onto them. This design reduces thread distortion and allows for more accurate torque readings. The result is a stronger, more reliable seal that can withstand the thermal and mechanical stress of hard driving and track use.

ARP Head Studs vs. Factory Bolts: Key Differences

Clamping Force Consistency

Factory head bolts use a torque-to-yield (TTY) design. They are stretched during installation and can only be used once. Over time, the clamping force can relax, especially after thermal cycling. ARP head studs are reusable and maintain their clamping force even after multiple disassemblies. They are torqued using either a specific torque number or a stretch gauge, ensuring consistent load across all fasteners.

Material and Strength

ARP uses aircraft-grade alloy steel, typically rated at 200,000 psi tensile strength for their standard studs and up to 220,000 psi for their custom-age 625+ series. Factory bolts are generally weaker and more prone to fatigue under high boost. ARP studs also feature a rolled thread design (rather than cut threads) which eliminates stress risers and increases fatigue life.

Installation and Reusability

Once factory TTY bolts are torqued to yield, they cannot be reused safely. ARP studs can be removed and reinstalled multiple times, making them ideal for engines that are frequently disassembled for inspection or upgrades. They also make head removal easier since the studs stay in the block, aligning the head during installation.

Cost Breakdown for ARP Head Stud Installation on a Subaru WRX

The total cost varies by region, shop rates, and whether you do the work yourself. Below is a more detailed breakdown for a typical WRX (EJ or FA engine):

ItemEstimated Cost
ARP Head Stud Kit (Subaru WRX specific)$200 – $350
Head Gasket Set (OEM or aftermarket multi-layer steel)$150 – $300
Engine Oil, Coolant, Sealer, and Other Fluids$80 – $150
Machine Work (if head resurfacing is needed)$100 – $250
Labor (professional shop, 6–10 hours)$600 – $1,200
Total Estimated Range$1,130 – $2,250

If you are performing the work yourself, the cost drops to roughly $400–$700 for parts and fluids. However, consider that a head gasket job on a Subaru boxer engine requires specialized tools and careful attention to alignment.

Step-by-Step Installation Process

Installing ARP head studs on a Subaru WRX is an involved process that requires removing the cylinder heads. Below is a detailed guide. Always consult the factory service manual for your specific model year (e.g., 2002–2014 EJ20/EJ25 or 2015+ FA20).

Tools and Supplies Needed

  • ARP head stud kit (with lubricant)
  • Torque wrench (ft-lb and in-lb) rated for ARP specifications
  • New head gaskets (OEM or MLS type)
  • Socket set, ratchets, extensions (including 12-point sockets for stud nuts)
  • Torque angle gauge (if using ARP's recommended method)
  • Engine oil, coolant, thread sealant for block threads
  • Shop towels, brake cleaner, scraping tool for gasket removal
  • Feeler gauge for checking deck flatness (optional)

Step 1: Prepare the Engine

Disconnect the battery. Drain engine oil and coolant. Remove the intake manifold, turbo assembly, exhaust components, timing belt/chain cover, and any accessories blocking cylinder head access. On most WRX engines, you will also need to remove the valve covers and camshaft sprockets. Label all connectors and hoses.

Step 2: Remove the Cylinder Heads

Unbolt the factory head bolts in the reverse of the tightening sequence (usually loose from the outside in). Lift the cylinder heads off the block. Be careful not to damage the dowel pins or mating surfaces. Place the heads on a clean surface. Check the head deck for warpage using a straightedge—warpage beyond 0.003 inches requires resurfacing.

Step 3: Clean and Inspect Block and Head Surfaces

Use a plastic scraper and brake cleaner to remove all old gasket material from the block deck and cylinder head surfaces. Do not use metal scrapers that could gouge the aluminum. Chase the head bolt holes in the block with a thread chaser (not a tap) to remove any debris or corrosion. Blow out the holes with compressed air.

Step 4: Install ARP Head Studs

Apply ARP recommended thread lubricant (usually supplied with the kit) to the block threads and the lower portion of the stud. Do not lubricate the upper threads where the nut will go—ARP specifies that the nut threads should be dry or lubricated as per their instructions. Hand-tighten each stud into the block until it bottoms out. Use a hex key or stud driver tool to fully seat the studs. Do not overtighten; they should be snug but not torqued.

The studs should protrude evenly above the deck.

Step 5: Install New Head Gaskets

Place the new head gaskets onto the dowel pins on the block. Ensure proper orientation (many MLS gaskets have a top/bottom marking). Do not use any sealer on MLS gaskets unless specified by the manufacturer. For EJ engines, consider using OEM Subaru gaskets or high-quality aftermarket units like Cometic or Six Star.

Step 6: Reinstall Cylinder Heads

Carefully lower the cylinder head onto the gasket and dowel pins. Make sure the head sits flush. Install the ARP washers (if included) and then the nuts. Do not tighten yet.

Step 7: Torque the ARP Head Studs to Specification

Refer to the ARP instruction sheet for your specific stud kit. Typical torque specs for a Subaru WRX ARP stud are:

  • ARP standard studs: 80 ft-lbs final torque in three steps (30, 60, 80 ft-lbs) using ARP lubricant on bolt threads.
  • ARP 625+ studs: 85–90 ft-lbs final torque.

Follow the factory tightening sequence (typically starting from the center and working outward in a spiral). Some ARP kits recommend a specific sequence; stick to that. After torquing all nuts to final spec, wait 30 minutes and re-torque to ensure the clamping load has stabilized.

Important: Do not use a torque angle gauge with ARP studs unless the instructions explicitly say so. Over-torquing can stretch the studs and compromise their strength.

Step 8: Reassemble the Engine

Replace timing components, valve covers, intake manifold, turbo, and all other parts in reverse order of disassembly. Use new gaskets where applicable. Refill with fresh engine oil and coolant. Prime the oil system before starting (disconnect the fuel pump relay and crank the engine until oil pressure registers).

Step 9: Start and Check

Start the engine and allow it to reach operating temperature. Check for coolant leaks, oil leaks, and abnormal noises. Listen for head gasket seepage. After the first heat cycle, re-torque the head studs once the engine has cooled (optional but recommended by some tuners). Perform a compression test to confirm even cylinder pressures.

Performance Benefits of ARP Head Studs on a WRX

Higher Boost Capability

The most immediate benefit is the ability to run higher boost pressures safely. With stock head bolts, many WRX owners report head gasket failures at boost levels above 20 psi on a turbocharged EJ. ARP studs allow 25–30 psi without gasket lift. This is essential for larger turbos like the Garrett GTX3076R or stock-frame upgrades.

Reduced Head Gasket Failure Rate

Even at moderate power levels, the clamping force of ARP studs reduces the likelihood of a blown head gasket. The uniform load distribution prevents localized lifting that can occur with factory TTY bolts. This is especially important for engines that see track time or aggressive daily driving.

Improved Engine Longevity

By keeping the cylinder head tightly sealed, combustion pressure is better contained. This reduces stress on the block, pistons, and rings. The engine runs cooler because there is no combustion gas leakage into the coolant passages. Many high-mileage WRX builds credit ARP studs for enabling 100,000+ miles of reliable high-boost operation.

Consistent Torque After Multiple Heat Cycles

Factory TTY bolts lose some clamping force after the first heat cycle. ARP studs maintain their torque more consistently, especially when using the recommended moly lube. Some tuners recommend a cold re-torque after the first 500 miles to ensure everything is settled.

Compatibility with Aftermarket Head Gaskets

Upgraded aftermarket head gaskets (like multi-layer steel or copper) require higher clamping forces to seal properly. ARP studs provide that force, making them necessary for any serious engine build. Without studs, even the best gaskets can fail.

Common Mistakes to Avoid

  • Not cleaning the block threads properly: Oil or debris in the threads can cause false torque readings and insufficient clamping. Always chase and blow out the holes.
  • Mixing lubricants: Use only the lubricant provided by ARP or specified in the instructions. Using engine oil or anti-seize can alter torque values by 20–30%.
  • Skipping the wait-and-re-torque step: Some studs relax after initial torquing. Waiting 30 minutes and re-torquing ensures a stable clamping load.
  • Using the wrong torque sequence: The tightening pattern must be followed to avoid warping the head. Never tighten from one end to the other.
  • Reusing old head gaskets: Always use new head gaskets when installing ARP studs. Used gaskets may have compression set and will not seal reliably.

Which ARP Head Stud Kit for Your WRX?

ARP offers several kits specifically for Subaru EJ and FA engines. The most common are:

  • ARP 260-4201: For 2002–2014 Subaru WRX/STI (EJ205/EJ257). Standard 8740 chromoly, 200,000 psi. Good for up to ~600 whp on stock sleeves.
  • ARP 260-4202: Same as above but with 625+ material (220,000 psi). Recommended for high-boost or nitrous applications.
  • ARP 260-4205: For FA20DIT WRX (2015+). Uses a unique stud length due to the different deck height.

Always verify your engine code before purchasing. Most WRX and STI engines from 2002–2014 use the same stud set (EJ series), but the FA20 requires a different kit. Check your VIN or engine serial number.

Conclusion

Installing ARP head studs on a Subaru WRX is not a simple bolt-on—it requires removing the cylinder heads and careful attention to detail. However, the payoff in reliability and boost headroom is well worth the effort. Whether you are building a 400 whp daily driver or a 600 whp track monster, ARP head studs provide the clamping force needed to keep the head gasket sealed under extreme conditions. Combined with a proper tune and supporting mods, they are one of the most effective upgrades for ensuring your EJ or FA engine stays together at high power levels. Always follow the manufacturer’s instructions, use quality gaskets, and consider professional installation if you are not comfortable with engine tear-down.

With ARP studs, your WRX engine will be ready for whatever boost you throw at it.