IAG 950 EJ25 Subaru Closed Deck Short Block For WRX, STI, LGT, FXT – 950 BHP

Part Details:

The IAG 950 Closed Deck EJ25 Short Block is built for Subaru enthusiasts pursuing extreme power levels where absolute engine stability and durability are required. Based on a fully CNC-machined closed-deck EJ25 case, this short block is engineered to eliminate the common failure points associated with factory open-deck and semi-closed-deck Subaru engines under high boost.

Designed to support builds targeting up to 950 BHP, the IAG 950 is intended for high-horsepower street cars, drag racing applications, and track-focused setups where cylinder stability, head gasket sealing, and internal strength are critical.

Closed Deck & Fire-Lock Design

The foundation of the IAG 950 is a fully machined closed-deck EJ25 case that significantly increases cylinder wall support under extreme cylinder pressure. This design minimizes bore distortion and improves long-term durability in high-boost environments.

To further enhance head gasket sealing at elevated power levels, the block features IAG Fire-Lock™ receiver groove machining. This system is designed to work in conjunction with IAG Fire-Lock™ head gaskets and is a key upgrade for preventing head gasket failure in high-horsepower and high-boost EJ applications.

Engine Internals & Construction

Internally, the IAG 950 is assembled using a carefully selected combination of forged and race-grade components designed to withstand extreme loads and RPM. The block is equipped with IAG-spec JE FSR forged pistons manufactured from 2618 alloy, featuring electroless nickel-plated crowns and ring lands for increased durability under high heat and pressure.

IAG-spec Tuff H-beam connecting rods with ARP 625+ rod bolts are used to provide exceptional strength and rigidity, while high-strength H13 wrist pins further improve reliability in extreme cylinder pressure environments. ACL or King race bearings are used throughout to support consistent oil clearances under demanding conditions.

Every short block is blueprinted, bored, honed, and assembled in-house by IAG technicians to ensure precise tolerances, consistent clearances, and repeatable performance at high power levels.

Reliability & Performance Benefits

At power levels approaching four digits, OEM-style EJ engine architecture becomes a significant liability. The IAG 950 addresses these limitations by combining closed-deck cylinder support, Fire-Lock sealing technology, and forged internals specifically chosen for extreme boost and aggressive tuning.

This short block is designed for builders who require a proven foundation capable of supporting big-turbo setups, E85 fuel systems, and demanding motorsport environments without sacrificing reliability.

Vehicle Fitment Overview

This short block is compatible with turbocharged Subaru EJ25 platforms, including WRX STI, Legacy GT, and Forester XT models. Full year-by-year compatibility is listed in the Vehicle Fitment tab above.

This is a high-performance short block, not a stock replacement. Vehicle configuration, cylinder head selection, and overall build goals should always be verified prior to purchase.

What’s Included

• Brand-new Subaru OEM EJ25 case halves converted to closed deck, bored and honed to 99.75mm
• IAG Fire-Lock™ receiver groove machining (Fire-Lock™ head gaskets required)
• Case machining for 14mm head studs (head studs sold separately)
• IAG-spec JE FSR 99.75mm 2618 forged pistons with electroless nickel-plated crowns and ring lands
• 0.250″ / 0.906″ H13 wrist pins with clips and skirt coating
• IAG-spec Tuff H-beam connecting rods with ARP 625+ rod bolts
• ACL or King race rod and main bearings
• New Subaru nitride-treated STI crankshaft (2017+)
• OEM Subaru case and main bolts

Compression Ratio

• 9.1:1 – EJ255 (D heads)
• 8.8:1 – EJ257 (B, V, W heads) with IAG Fire-Lock™ head gaskets

Required Components

• IAG Fire-Lock™ 0.051″ head gaskets with IAG-spec alloy ring set (PN: IAG-ENG-1741)
• 14mm head studs (sold separately)

Installation & Build Notes

• Professional installation is strongly recommended
• ECU tuning is required
• Supporting modifications (fueling, turbo system, cooling, oiling) are mandatory at this power level
• Final power capability depends on the complete engine build, tuning strategy, and operating conditions

Recommended Supporting Upgrades

• Air / Oil Separator (AOS) – helps reduce oil vapor ingestion and protect the intake system
• Oil pickup and baffle upgrades – improves oil control and reduces bearing failure risk
• Long block installation kits – simplifies installation with required gaskets and hardware
• Engine installation fluid kits – includes break-in oil and coolant for first startup

Recommended Supporting Upgrades

• Air / Oil Separator (AOS) – helps reduce oil vapor ingestion and protect the intake system
• Oil pickup and baffle upgrades – improves oil control and reduces bearing failure risk
• Long block installation kits – simplifies installation with required gaskets and hardware
• Engine installation fluid kits – includes break-in oil and coolant for first startup

Performance Airflow Upgrades

• Corsa Veloce Stradale Rear-Facing Intake Manifold– increases airflow and supports high-horsepower EJ engine builds

This short block is part of our broader engine performance upgrades, designed to support high-output builds with strength, reliability, and long-term durability.