IAG 950 EJ25 Destroked 2.35L Closed Deck Short Block For WRX, STI, LGT, FXT - 950BHP

IAG’s 950 EJ25 2.35 L Destroked Closed Deck Short Block delivers track-level power, supporting up to 950 BHP, while still offering the dependability needed for everyday driving. This hand assembled block is based off of our IAG 950 short block, and features a 2.0L FHI crankshaft, custom IAG Spec +2mm H-beam forged connecting rods and ARP 625+ rod bolts. Also included in the assembly are JE 99.75mm FSR 2618 custom pistons that have been treated with electroless nickel-plating, creating a hard-wearing surface that offers detonation resistance and heat reflection. This short block strikes the perfect balance for street use along with high-revving racing applications, offering unmatched reliability and longevity.

Featuring a shorter stroke, these +2 rod engines reduce piston speeds, optimizing the rod-to-stroke ratio and increasing piston dwell time at top dead center. This results in improved combustion efficiency and reduced stress on engine components at high RPMs. In terms of performance, this means increased power output, extended ring life, and the ability to rev up to 8,500 RPM making this short block an ideal choice for track days, rally events, or drag racing applications.

The IAG 950 EJ25 Short Block starts with brand new Subaru 2.5L engine case halves. Our expert machinists machine the assembled case halves in our Haas VF-4SS CNC mill to accept the IAG Closed Deck inserts, transforming the block into a solid deck. Next, a deck pair of deck plates are attached and the short block is bored and honed to 99.75mm in our in-house Sunnen SV-30 computer controlled cylinder hone. IAG's in-house honing process allows us to set custom piston to wall clearances to ensure quiet operation and reduced oil consumption. The Haas mill also cuts a groove at the top of each cylinder to accept the Fire-Lock™ head gasket rings and drills each head bolt hole for 14mm head studs. The modified case halves are then assembled using a new 2.0L FHI crankshaft, custom IAG Spec +2mm H-beam forged connecting rods and ARP 625+ rod bolts, along with JE 99.75mm FSR 2618 custom pistons. IAG Short blocks feature ACL rod and main bearings and are all balanced and blueprinted. Finally, the case halves are sealed with new OEM main/case bolts and sealant.

The IAG 950 EJ25 2.35L Destroked 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 the combustion chamber sealing from the fluid sealing aspects of the head gaskets. Our machinists carefully machine a lip at the top of each cylinder to accept the "Fire-Lock™" ring. With the ring locked in place, it stands proud above the deck, providing a superior seal. The separate gasket bodies take care of sealing oil and coolant passages and keeping them out of the combustion chamber. 14mm Head studs (Not Included) hold the assembly together.

Our innovative closed deck system significantly increases the strength of the OEM case halves. This process supports the cylinder walls at the top of the case in order to prevent flexing and possible cracking where the case bolt reliefs are cut into the back of the cylinder wall. During the installation process, we machine the assembled case halves in our Haas VF-4SS CNC mill to accept the IAG Closed Deck inserts. Once the case has been machined we heat it in an oven while freezing the specially machined inserts with liquid nitrogen. The inserts are then pressed into place and then machined to a mirror finish. Our distinctive inserts feature small passages that allow needed coolant flow to the deck surface. This means that the closed deck system does not affect the block's cooling ability and will not cause overheating, even in daily drivers.

The IAG 950 Short Block features JE 99.75mm FSR 2618 custom pistons, engineered to deliver outstanding performance for both street driving, as well as for drag and rally racing applications. These pistons feature thicker ringlands and are treated with electroless nickel-plating, resulting in a stronger piston that can stand up to highly boosted applications. Additionally, they come equipped with .240" H13 tool steel wrist pins, providing a significant upgrade over standard chromoly pins, ensuring enhanced reliability under extreme conditions.

A common failure point of the OEM Subaru short block are the piston ringlands. The metal ledges on the pistons that hold the compression rings in place can withstand regular usage but are prone to failure when used with modified components. Cracked or broken ringlands often lead to increased oil consumption and eventual bearing failure if the oil is not closely monitored. In contrast, the increased ringland thickness on the custom JE pistons used in the IAG 950 Short Block are designed to match up to 950’s capabilities, ensuring durability and reliability even under high-performance conditions.

The OEM EJ25 pistons continue to be produced using a hypereutectic cast design. This casting method is susceptible to irregularities in both the casting process and the materials used, leading to potential weaknesses in the pistons. This is where our custom JE pistons come in; forged from a durable 2618 T6 Alloy with a unique silicone additive, these JE pistons effectively absorb the direct shock and impact of combustion. Engineered to withstand ringland damage due to detonation and preignition, they feature a higher strength material and have been custom designed to feature thicker ringlands.

Our team of certified Subaru specialists at IAG Performance takes great care in assembling each IAG 950 Short Block. These specialists have now built over 14,000 Subaru engines and counting. Equipped with an advanced selection of tooling and state-of-the-art equipment, we guarantee the quality of all our engine blocks. Each block is meticulously crafted and thoroughly checked, ensuring the highest standards of quality assurance. IAG’s hand-assembled Short Blocks make it easy to upgrade your EJ25 Subaru engine, just leave the technical work to us, and we’ll provide you with a superior short block that’s ready to install.