IAG 1000 FA20 DIT Subaru Closed Deck Short Block - 1000 BHP - 2015-21 WRX

The IAG 1000 FA20 DIT Subaru Closed Deck Short Block is built for enthusiasts who want big power without sacrificing reliability. Designed to support up to 1000 BHP, this combination delivers the strength needed for serious boost while maintaining the durability required for real street use. Inside, you’ll find IAG-Spec H-Beam forged connecting rods paired with IAG-Spec JE pistons featuring an electroless nickel-plated coating and H13 tool steel wrist pins. The case is precision-machined to accept our proven Fire-Lock head gasket system and 14mm head studs (sold separately). Each IAG 1000 short block is hand-assembled using ACL or King rod and main bearings for consistent, reliable performance, whether you're street driving, drag racing, or out on the track.

The IAG 1000 FA20 DIT Subaru Closed Deck Short Block uses a precision-machined closed deck conversion to significantly reinforce the factory Subaru case halves. By adding structural support around the tops of the cylinder walls, the design limits cylinder wall movement and reduces the potential for cracking in high-stress areas like the case bolt reliefs. The assembled case halves are machined in our Haas VF-4SS CNC mill to accept IAG Closed Deck inserts, then the block is heated while the inserts are cryogenically cooled so they can be pressed into place for a secure mechanical fit. Once installed, the deck surface is machined to a smooth, mirror finish. Each insert is designed with built-in coolant passages so proper flow to the deck surface is maintained, meaning you get the added strength of a closed deck without sacrificing cooling performance.

The IAG 1000 FA20 DIT Subaru Closed Deck Short Block for the 2015–2021 WRX begins with brand-new Subaru FA20F engine case halves that are precision-machined in our Haas VF-4SS CNC mill to accept IAG Closed Deck inserts, converting the factory open deck into a much stronger closed deck foundation built to handle serious cylinder pressure. Once the inserts are installed, deck plates are bolted on, and the block is bored and honed to 86.25mm using our Sunnen cylinder hone, allowing us to dial in exact piston-to-wall clearances for proper ring seal, quiet operation, and reduced oil consumption. While it’s on the mill, we machine a groove at the top of each cylinder for the Fire-Lock head gasket system and drill the head bolt holes to accept 14mm head studs. From there, the case halves are assembled with a brand-new Subaru FA20 DIT crankshaft, IAG-Spec H-Beam forged connecting rods with ARP 625+ rod bolts, and ACL or King Race rod and main bearings. Finally, every short block is balanced, blueprinted, and sealed with new OEM main and case bolts and factory sealant, delivering a rock-solid foundation built to handle up to 1000 BHP.

The IAG 1000 FA20F Subaru Closed Deck Short Block features our proprietary “Fire-Lock” Head Gasket System. This system has been proven in our record-setting race cars to be the strongest Subaru head gasket system ever produced. To achieve these results, our engineers separated combustion sealing from the oil and coolant sealing functions of a traditional head gasket. Each cylinder is precision-machined with a counterbore step at the top to accept the Fire-Lock ring that mechanically locks into place and creates an extremely secure combustion seal. The independent gasket bodies handle sealing the oil and coolant passages, keeping fluids out of the combustion chamber where they don’t belong. The entire assembly is secured using 14mm head studs for maximum clamping force (Fire-Lock Gaskets and 14mm Head Studs sold separately).

The pistons in the IAG 1000 FA20 DIT Subaru Closed Deck Short Block are built to handle the demands of serious performance use. Developed in partnership with JE, these IAG-Spec pistons are manufactured from 2618 alloy and feature an electroless nickel-plated coating for added durability. Extra-thick ring lands help resist collapse under high cylinder pressure, lateral gas ports to help promote piston ring seal under higher boost, while upgraded .250" wall H13 tool steel offset wrist pins are designed to support power levels up to 1000 BHP without bending or failure. Each piston also includes JE’s Perfect Skirt coating to promote smooth operation and long-term reliability.