IAG / Crest CNC Billet Aluminum EJ25 Subaru Case Halves For WRX, STI, Forester XT & Legacy GT

The IAG Performance / Crest CNC Billet Aluminum EJ25 Case Halves are the same premium-grade case halves used in our cutting-edge Stage X Billet Short Block, which has revolutionized the Subaru performance tuning market by reinventing the EJ and addressing virtually every weakness that exists in max-power builds. The EJ25 Case Halves are engineered to eliminate case flex in high-power EJ builds, making it possible to reliably run at a power output rating of 1150+BHP. With features like radiused coolant and oil galleries to improve flow, a 4-bolt bottom end for added strength, and replaceable iron sleeves that make rebuilds easier, these case halves offer a rock-solid foundation to build upon.

The IAG Performance / Crest CNC Billet Aluminum EJ25 Case Halves are machined by Crest CNC (formerly Willall), renowned for their precision-machined billet aluminum engine blocks and components. With Crest’s proven track record of producing blocks that endure the rigors of high-output engines, these case halves provide an unbeatable foundation for those pushing the limits of performance.

The IAG Performance / Crest CNC Billet Aluminum EJ25 Case Halves are engineered with numerous advanced features that enhance strength and reliability. The halves are precision machined from solid 6061-T6 aerospace aluminum billet and reinforced with Darton Ductile Iron Sleeves. An advanced hard anodized coating protects against marking and staining, while their enhanced strength and stiffness far surpass the stock case, making them an excellent choice for high-power builds. Additionally, increased material thickness has been strategically added in all known weak points, particularly around the head studs and bottom end location, enhancing the block's resilience.

Additional innovations featured in the IAG / Crest CNC Billet Aluminum EJ25 Case Halves include a unique 4-bolt bottom end design that provides extra strength and stability. The case's bolt threads are rolled, rather than conventionally cut, ensuring a solid grip on hardware. The halves also maintain full cooling system operations, while incorporating the use of radiused coolant and oil galleries for improved flow and less foaming and/or turbulence. Finally, the Case Halves feature compatibility with all factory engine bay ancillaries (i.e., AC/PS/etc.).

The IAG Performance / Crest CNC Billet Aluminum EJ25 Case Halves can be machined to accommodate the optional IAG Fire-Lock system. Our proprietary "Fire-Lock" receiver groove machining is designed for compatibility with our IAG "Fire-Lock" Head Gaskets. 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 firmly above the deck, providing a superior seal. The separate gasket bodies take care of sealing oil and coolant passages, while keeping them out of the combustion chamber. 14mm Head studs hold the assembly together. (IAG "Fire-Lock" System, Head Gaskets and Head Studs Sold Separately).