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

Part Details:

The IAG 1150 High Compression Closed Deck EJ25 Short Block is designed for Subaru EJ25 builds that demand extreme power while prioritizing faster spool and improved throttle response. Rated for builds targeting up to 1,150 BHP, this short block combines IAG’s CNC-machined closed-deck reinforcement with high-compression internals to deliver maximum cylinder stability under high boost.

This configuration is ideal for big-turbo street cars and competitive motorsport applications where responsiveness and power delivery are just as important as ultimate strength.

High Compression Closed Deck Design

Unlike standard compression short blocks, the high compression IAG 1150 is engineered to improve off-boost response and turbo spool characteristics. The fully machined closed-deck EJ25 case provides superior cylinder wall support, helping the engine withstand elevated cylinder pressures associated with high boost and increased compression ratios.

This makes the high compression variant a strong choice for drivers seeking sharper throttle response and improved drivability without sacrificing the durability required for extreme horsepower.

Engine Internals & Construction

The IAG 1150 High Compression short block is assembled with race-grade components selected to handle extreme engine loads. It features IAG-spec JE FSR forged pistons manufactured from 2618 alloy, with electroless nickel-plated crowns and ring lands for enhanced heat resistance and durability. The high-compression piston design supports improved combustion efficiency while maintaining strength under boost.

IAG-spec +2mm Tri-Beam connecting rods with ARP 625+ rod bolts provide exceptional rigidity, while high-strength H13 wrist pins support sustained high RPM and cylinder pressure. An IAG-spec billet crankshaft further increases bottom-end strength, complemented by ACL or King race bearings and ARP main bolts.

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

Reliability & Performance Benefits

At elevated compression ratios and boost levels, OEM-based EJ engine architecture quickly becomes a liability. The IAG 1150 High Compression short block addresses these challenges by combining closed-deck cylinder support, pinned mains, Fire-Lock sealing technology, and billet rotating components to deliver reliable performance in demanding environments.

This short block is intended for builders who want maximum power capability with enhanced responsiveness for aggressive street or motorsport use.

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 high-performance, race-oriented 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 high-compression pistons with electroless nickel-plated crowns and ring lands
• 0.250″ wall / 0.927″ diameter 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

• 9.9:1 – EJ255 (D heads)
• 9.5:1 – EJ257 (B, V, W heads)

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
• Supporting modifications (fuel system, turbo system, cooling, oiling) are essential
• High compression setups require careful tuning and fuel selection
• 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

Learn more about IAG Performance engine and reliability solutions