IAG 1150 2.5L Subaru Closed Deck Short Block For WRX, STI, LGT, FXT – 1150 BHP

Part Details:

The IAG 1150 Closed Deck EJ25 Short Block represents the highest tier of engine foundation for Subaru EJ25 applications, built for extreme horsepower and competitive motorsport use. Rated for builds targeting up to 1,150 BHP, this short block is engineered to handle sustained high boost, elevated RPM, and severe engine loads where lower-tier EJ blocks reach their limits.

Designed for drag racing, big-turbo street builds, and serious track applications, the IAG 1150 combines a reinforced closed-deck case with race-grade internals and precision machining to deliver maximum strength, stability, and long-term durability at extreme power levels.

Closed Deck, Pinned Mains & Fire-Lock Design

At the core of the IAG 1150 is a fully CNC-machined closed-deck EJ25 case that provides exceptional cylinder wall support under extreme cylinder pressure. To further enhance bottom-end rigidity, the case is machined for 9.5mm pinned mains and line-honed, reducing main cap movement under heavy load.

For head gasket sealing at extreme boost 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 critical for maintaining combustion sealing in high-horsepower, high-boost EJ builds.

Engine Internals & Construction

Internally, the IAG 1150 is assembled using race-focused components selected for maximum strength and durability. The short block features IAG-spec JE FSR forged pistons manufactured from 2618 alloy, with electroless nickel-plated crowns and ring lands for improved resistance to heat and detonation. High-strength H13 wrist pins are used to support extreme cylinder pressure and high RPM operation.

IAG-spec +2mm Tri-Beam connecting rods with ARP 625+ rod bolts provide exceptional rigidity, while an IAG-spec billet crankshaft replaces the factory-style unit to further increase strength and reliability in extreme power applications. ACL or King race bearings and ARP main bolts complete the bottom-end assembly.

Each short block is fully blueprinted, bored, honed, and assembled in-house by IAG technicians to ensure precise tolerances, consistent oil clearances, and repeatable performance at the highest power levels.

Reliability & Performance Benefits

At power levels exceeding four digits, OEM-based EJ engine architecture becomes a significant limitation. The IAG 1150 addresses these challenges by combining closed-deck cylinder support, pinned mains, Fire-Lock sealing technology, and billet rotating components to create a foundation capable of withstanding extreme boost and sustained competition use.

This short block is intended for builders who require maximum reliability in aggressive motorsport environments where failure is not an option.

Vehicle Fitment Overview

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

This is a race-focused performance short block, not a stock replacement. Vehicle configuration, cylinder head selection, and overall build strategy 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
• Machined for 9.5mm pinned mains and line-honed
• IAG Fire-Lock™ receiver groove machining (Fire-Lock™ head gaskets required)
• Machined for 14mm head studs
• IAG-spec JE FSR 99.75mm 2618 forged pistons with electroless nickel-plated crowns and ring lands
• 0.250″ / 0.927″ H13 wrist pins with clips and skirt coating
• IAG-spec +2mm Tri-Beam connecting rods with ARP 625+ rod bolts
• ACL or King race rod and main bearings
• IAG-spec billet crankshaft
• ARP main bolts

Compression Ratio

• 8.5:1 – EJ255 (D heads)
• 8.2:1 – EJ257 (B, V, W heads) with standard thickness head gasket

Required Components

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

Installation & Build Notes

• Professional installation is mandatory at this power level
• ECU tuning is required
• Comprehensive supporting modifications (fuel system, turbo system, cooling, oiling) are essential
• 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

Performance Airflow Upgrades

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

Learn more about IAG Performance engine and reliability solutions