IAG 750 EJ25 Subaru Closed Deck Short Block For WRX, STI, LGT, FXT – 750BHP

Part Details:

Designed for high-power Subaru EJ25 builds, the IAG 750 Closed Deck Short Block provides a substantially reinforced engine foundation for applications targeting up to 750 BHP. The closed deck configuration adds critical support around the cylinder walls, helping the engine withstand extreme boost levels where factory open-deck cases quickly reach their limits.

This short block is commonly used in big-turbo street cars, E85 builds, and track-focused setups where long-term durability and head gasket stability are essential.

Closed Deck Design & Strength

A key upgrade over lower-tier EJ short blocks is the fully machined closed deck conversion. By minimizing cylinder wall flex under high cylinder pressure, the closed deck design improves bore stability and helps reduce the risk of head gasket failure commonly seen in high-boost EJ applications.

For aggressive builds running elevated boost, sustained RPM, or advanced fueling strategies, the closed deck layout provides a more stable and reliable starting point.

Engine Internals & Construction

Inside the assembly, the IAG 750 uses IAG-spec Tri-Beam forged connecting rods secured with ARP 625+ rod bolts and paired with ACL or King performance bearings. This rod and bearing combination is engineered to maintain rigidity and stability under extreme engine loads and elevated RPM.

The short block is equipped with IAG-spec JE 99.75mm forged pistons manufactured from 2618 alloy. These pistons are designed for heavy boost applications, improved heat resistance, and increased protection against ringland failure. A flow-optimized dome design supports efficient combustion while handling the stress associated with high-output EJ builds.

Reliability Benefits

As power levels rise, OEM EJ engines often suffer from ringland failure, cylinder distortion, or head gasket issues. The IAG 750 Closed Deck Short Block addresses these weak points by combining reinforced case architecture with forged internal components better suited for extreme cylinder pressure and hard use.

Each short block is assembled using 100% brand-new components, including new EJ25 case halves and a nitride-treated STI crankshaft. Precision machining, strict tolerances, and professional assembly ensure consistent performance and long-term reliability.

Vehicle Fitment Overview

This short block supports turbocharged Subaru EJ25 applications, including WRX STI models. Full year-by-year compatibility is listed in the Vehicle Fitment tab above.

This is a performance short block, not a stock replacement. Vehicle configuration, cylinder head selection, and 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-spec JE FSR 99.75mm 2618 forged pistons with ring set, 0.210″ 9310 steel wrist pins, clips, and skirt coating
• IAG-spec Tri-Beam forged connecting rods with ARP 625+ rod bolts
• ACL or King performance rod and main bearings
• New Subaru nitride-treated STI crankshaft (2017+)
• OEM Subaru case and main bolts

Compression Ratios

• 9.5:1 – EJ255 (D heads) with OEM head gasket
• 8.9:1 – EJ257 (B, V, W heads) with OEM head gasket
• 9.6:1 – S20 heads (no combustion chamber modification) with OEM head gasket
• 9.1:1 – EJ255 (D heads) with 0.039″ JE ProSeal head gasket
• 8.6:1 – EJ257 (B, V, W heads) with 0.039″ JE ProSeal head gasket
• 9.2:1 – S20 heads (no combustion chamber modification) with 0.039″ JE ProSeal head gasket

Installation & Build Notes

• Professional installation is strongly recommended
• ECU tuning is required
• Supporting modifications (fueling, turbo, cooling, oiling) are necessary for high-power operation
• Final power capability depends on the complete 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