The Role of Head Gaskets in Forced Induction Engines

Head gaskets are among the most critical sealing components in any internal combustion engine. They sit between the engine block and cylinder head, forming a high-pressure seal that keeps combustion gases in the cylinders, coolant in its passages, and oil in its galleries. In a turbocharged Subaru WRX, the demands placed on these gaskets are far greater than in a naturally aspirated engine. The combination of elevated cylinder pressures, higher operating temperatures, and the engine’s unique boxer layout creates a challenging environment where only the best gaskets can survive long-term.

A failure of the head gasket in a WRX can lead to catastrophic damage: coolant and oil mixing, loss of compression, overheating, and potential engine failure. For owners pushing beyond stock power levels, upgrading to a premium gasket like the ARB unit becomes not just a performance upgrade but a reliability necessity.

Why Subaru WRX Engines Are Prone to Head Gasket Failure

The EJ-series and FA-series engines found in the WRX have a well-documented history of head gasket issues, especially in earlier models. The flat-four design means the cylinder heads are mounted horizontally, which creates unique thermal and mechanical stresses. Stock gaskets often use a multi-layer steel (MLS) design, but with thin layers that can fatigue over time. When boost levels are increased from the factory 12–14 psi to 20+ psi, the stock gasket’s clamping force and material strength become marginal. Additionally, uneven torque sequences and improper cooling system maintenance accelerate failure. A successful upgrade must address both the gasket’s construction and the installation procedure.

Understanding ARB Head Gasket Upgrades

ARB head gaskets are engineered specifically for high-performance Subaru applications. Unlike standard replacement gaskets, ARB units are designed to handle sustained high cylinder pressures and elevated temperatures without losing sealing integrity. They are available in various thicknesses to adjust compression ratio, making them a versatile choice for both stock-engine builds and fully forged setups.

Materials and Construction

ARB gaskets are constructed from a proprietary composite material that combines a robust metal core with a high-temperature elastomeric coating. This provides better conformability to surface irregularities than pure MLS gaskets, while still offering the strength needed to resist combustion pressure. The material is engineered to maintain its clamping force through repeated heat cycles, reducing the risk of gasket relaxation that can lead to leaks. The fire ring—the area around each cylinder bore—is reinforced with a thicker stainless steel element to prevent blowout under extreme boost.

Key Differences from OEM Gaskets

The most significant differences between ARB head gaskets and OEM units come down to material quality, thickness options, and sealing surface design. OEM gaskets are built to a cost target and are optimized for normal driving conditions. ARB gaskets use higher-grade alloys in the core and a more resilient outer coating. Additionally, ARB offers gaskets in 0.5mm, 0.8mm, and 1.0mm thicknesses (stock is typically 0.6mm), allowing tuners to fine-tune quench clearance and compression ratio. This is critical when running higher boost on pump gas or ethanol blends.

Power Gains – What to Expect

Head gaskets themselves do not directly generate horsepower. Instead, they enable the engine to safely operate at power levels that would destroy a stock gasket. When correctly installed and paired with appropriate tuning, ARB head gaskets can unlock 30–50+ wheel horsepower gains. The gains come from three main areas: the ability to run higher boost pressure, the capacity to advance ignition timing without detonation, and the ability to hold that power reliably across the entire RPM range.

Real-World Dyno Results

Numerous Subaru WRX owners have documented dyno runs after ARB gasket installation. On a stock-block 2004 WRX with a VF39 turbo upgrade and a conservative tune, swapping from a compromised OEM gasket to ARB units and adding 3 psi of boost resulted in a gain of 36 whp and 42 lb-ft of torque. On a fully built EJ257 with a GTX3076R turbo, ARB gaskets allowed the tuner to run 28 psi on E85, yielding over 500 whp—power levels that would lift the heads or blow out stock gaskets within minutes. These results are consistent across multiple platforms when supporting mods are in place.

How ARB Gaskets Enable Higher Boost and RPM

The primary limitation at high boost is head lifting—where cylinder pressure physically separates the cylinder head from the block, breaking the seal. ARB gaskets, with their reinforced fire rings and higher compressive strength, resist this lifting force. Additionally, the ability to select a thicker gasket slightly lowers compression ratio, which reduces the octane requirement and allows safer high-boost operation. This also permits higher RPM operation because the gasket can maintain its seal under the increased inertia forces generated at 7,000+ rpm.

Installation Guide – Step-by-Step

Installation of ARB head gaskets is not for the faint of heart. It requires meticulous attention to detail, proper tools, and a clean workspace. Subaru boxer engines are particularly sensitive to head gasket alignment and torque accuracy. Below is a comprehensive guide to ensure a successful installation.

Tools and Parts Required

  • ARB head gaskets (correct thickness for your build)
  • ARP head studs or OEM head bolts (recommended to replace)
  • Torque wrench rated for ft-lb and in-lb (calibrated)
  • Engine degreaser and brake cleaner
  • Plastic scraper (do not use metal on sealing surfaces)
  • Straightedge and feeler gauges for checking head flatness
  • Assembly lube for stud threads and washers
  • Coolant and oil for refill

Preparation and Disassembly

Begin by disconnecting the battery and draining the coolant and oil. Remove the intake manifold, exhaust manifold, turbocharger, and all ancillary components that block access to the cylinder heads. Timing belt or timing chain must be removed along with the camshaft gears. Mark all timing components before removal. The cylinder heads can then be unbolted and lifted off. Separate the heads from the block and carefully set them aside. Do not allow debris to fall into the open cylinders.

Surface Preparation – Critical

This step determines success or failure. Both the engine block deck and cylinder head mating surfaces must be absolutely clean and free of old gasket material, oil, and coolant residue. Use a plastic scraper to remove all traces of the old gasket. Follow with a green Scotch-Brite pad and brake cleaner to shine the surfaces. Check the block deck for warpage using a straightedge and feeler gauge; maximum allowable is 0.002 inches across the entire surface. If the block deck is warped, the block must be decked before proceeding. Similarly, check each cylinder head for flatness; experience shows many used EJ heads are slightly warped and need resurfacing.

Installing the ARB Gasket

Place the new ARB gasket onto the clean block deck. Pay attention to orientation—most ARB gaskets have a marking indicating “top” or “this side up.” The gasket should sit perfectly centered over the cylinder bores and all coolant/oil passages. Do not use any sealant unless specified by ARB (some coatings are designed to seal dry). Gently tap the gasket into position with a soft mallet if needed.

Torquing the Head Bolts Correctly

If using ARP head studs, follow the manufacturer’s torque sequence and values. Typically, ARP studs for Subaru require a three-step process: first to 30 ft-lb, then 60 ft-lb, then a final angle of 90 degrees on each bolt. If using OEM TTY bolts, they must be replaced with new ones and torqued to factory specifications using a torque-angle gauge. Always work in the factory-specified tightening pattern (usually a progressive inward-outward sequence).

Reassembly and Initial Start-Up

Reinstall the timing belt/chain, set valve timing, and reassemble all components in reverse order. Fill with fresh coolant and oil. Before starting, crank the engine with the ignition and fuel injectors disabled to build oil pressure. Then start the engine and let it idle for 15–20 minutes to allow the gasket to bed in. Check for coolant leaks and listen for any unusual sounds. A second torque re-check after initial heat cycling is recommended if using studs.

Supporting Modifications for Maximum Gains

Winning the head gasket lottery is only part of the equation. To realize the 30+ hp gains, the rest of the engine system must support the higher output.

Engine Tuning and Fuel System

An upgraded head gasket alone will not increase power. A proper tune from a Subaru specialist is mandatory. The tuner will increase boost, adjust fuel maps, and optimize ignition timing. On pump gas (93 octane), 20–22 psi is a safe limit with ARB gaskets; on E85, 25–30 psi is achievable. The fuel system must keep up: larger injectors (at least 1,000 cc/min), a high-flow fuel pump (e.g., AEM 50-1000 or Walbro 450), and possibly an upgraded fuel pressure regulator.

Upgraded Turbo and Intercooler

To see the full 30+ hp gain, a larger turbocharger is typically necessary. A VF39 or VF48 hybrid can support 300–350 whp, but a BorgWarner EFR or Garrett GT series will push beyond 400 whp. With higher boost comes higher intake air temperature; an upgraded front-mount intercooler (FMIC) or a larger top-mount intercooler is essential to prevent detonation. The ARB gaskets ensure the engine can handle the thermal and pressure load, but the intercooler must keep charge air cool.

Cooling System Upgrades

High boost generates substantial heat. A high-flow water pump, larger radiator, and oil cooler help maintain consistent operating temperatures. Overheating is the enemy of any head gasket upgrade; combining ARB gaskets with a 170°F thermostat and an aluminum radiator provides a safety margin. Additionally, using a coolant additive like Water Wetter can reduce hot spots.

Common Pitfalls to Avoid

  • Incorrect gasket thickness: Using a gasket that is too thick or too thin can alter the quench clearance and compression ratio, causing detonation or poor performance. Measure your piston protrusion and select the appropriate ARB gasket thickness.
  • Neglecting head studs: Reusing old head bolts or studs is a common mistake. OEM TTY bolts lose clamping force after one use. Always upgrade to ARP head studs for reliable clamping.
  • Skipping surface flatness check: Many DIY installers assume the block and head are flat. A 0.003-inch warp can cause a leak around the fire ring. Spend the time to check and resurface if needed.
  • Incorrect torque sequence: Torquing in a random order or using too much force on one bolt can distort the head. Always follow the manufacturer’s sequence and final angle.
  • Ignoring cooling system: Running high boost with a clogged radiator or weak water pump will quickly overheat the engine and compromise the gasket seal.

Cost Considerations and ROI

An ARB head gasket set for a Subaru WRX runs between $150 and $250, depending on thickness. Compare that to the cost of a complete engine rebuild after a gasket failure ($2,500–$5,000+). Even if you pay a professional shop $1,000–$1,500 for installation, the total investment is under $2,000. For a 30+ whp gain and much higher reliability, the return on investment is excellent. Many owners find the upgrade pays for itself by preventing future engine damage, especially when running a Stage 2 or Stage 3 setup. For those looking at ARB’s official website for technical details, and for community builds on iWSTI forums, the consensus is clear: it’s one of the smartest upgrades for a boosted Subaru.

Conclusion

ARB head gaskets are a proven solution for turbocharged Subaru WRX owners seeking both power and peace of mind. By enabling higher boost levels, protecting against head lift, and offering flexibility in compression ratio selection, these gaskets unlock genuine 30+ horsepower gains when paired with proper tuning and supporting modifications. The installation requires mechanical competence, but the result is an engine that can deliver its power reliably track day after track day. For anyone planning to push their WRX beyond stock limits, upgrading to ARB head gaskets is not just an option—it is the foundation of a durable high-performance build.