IAG 800 FA20 DIT Subaru Closed Deck Short Block for 2015-21 WRX – 800 BHP

Part Details:

The IAG 800 FA20 DIT Closed Deck Short Block is a reinforced engine foundation designed for 2015–2021 Subaru WRX models targeting higher power levels than the factory FA20 architecture can reliably support. Rated for builds up to 800 BHP, this short block is engineered for high-boost applications where increased cylinder stability and durability are essential.

By combining a closed-deck conversion with forged internals and upgraded machining, the IAG 800 provides a strong and dependable platform for big-turbo street builds and track-focused applications pushing beyond the limits of open-deck FA20 engines.

Closed Deck Design & Case Machining

Each IAG 800 FA20 short block starts with brand-new OEM Subaru FA20 case halves that are converted to a closed-deck configuration. This reinforcement dramatically improves cylinder wall support, reducing bore distortion under high boost and helping prevent common failures associated with elevated cylinder pressure.

The case is also machined for improved oiling and then bored and honed to 86.25mm, ensuring proper lubrication and consistent clearances under high load and RPM.

Engine Internals & Components

The rotating assembly features IAG-spec forged pistons measuring 86.25mm, designed to withstand increased cylinder pressure while maintaining reliability for high-performance street and track use. These pistons are paired with carbon steel wrist pins and a matched ring set for dependable sealing under boost.

IAG-spec H-beam connecting rods secured with ARP2000 rod bolts provide a significant strength upgrade over factory components. ACL or King XPG rod and main bearings are used throughout to support consistent oil clearances and durability. A new OEM Subaru FA20 DIT WRX crankshaft completes the assembly.

Reliability & Performance Benefits

As power levels increase beyond moderate upgrades, open-deck FA20 short blocks can become a reliability concern. The IAG 800 Closed Deck FA20 DIT addresses these limitations by reinforcing the cylinder structure and upgrading internal components to better handle sustained boost and higher RPM operation.

This short block is well-suited for aggressive street builds, track days, and high-output turbo setups where long-term reliability is a priority.

Vehicle Fitment Overview

This short block is designed for Subaru WRX models equipped with the FA20 DIT engine. Full year-by-year compatibility is listed in the Vehicle Fitment tab above.

This is a performance short block and not a stock replacement. Vehicle configuration, supporting modifications, and tuning goals should always be verified prior to purchase.

What’s Included

• Brand-new OEM Subaru FA20 case halves converted to closed deck
• Case machining for improved oiling
• Bored and honed to 86.25mm
• IAG-spec 86.25mm forged pistons with ring set
• 0.150″ x 2.250″ carbon steel wrist pins
• IAG-spec H-beam connecting rods with ARP2000 rod bolts
• ACL or King XPG rod bearings
• ACL or King XPG main bearings
• New OEM Subaru FA20 DIT WRX crankshaft
• OEM Subaru case and main bolts
• OEM oil plug pre-installed at oil pan location

Compression Ratio

• 10.5:1 compression ratio with standard head gasket thickness

Installation & Build Notes

• Professional installation is strongly recommended
• ECU tuning is required
• Supporting modifications (fuel system, turbocharger, cooling) are necessary for higher power levels
• Final power capability depends on the complete build and tuning strategy

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