The IAG Stage 4 Extreme Short Block starts with brand new Subaru 2.5L EJ25 engine case halves. The case halves are split and the main webs are CNC machined in our Haas VF-4SS CNC mill for 9.5mm pins to reduce distortion and movement of the case in extreme conditions. The case halves are then reassembled and IAG machines the case to accept the IAG CLOSED Deck Inserts that transform the block into a solid deck. The unique inserts feature small passages that allow needed coolant flow to the deck surface. Next the case is CNC drilled and tapped to fit 14mm head studs. Utilizing larger 14mm head studs with ARP nuts and washers, reduces the chances of the heads lifting under extreme boost conditions. Our program then incorporates cutting o-ring grooves around each bore of the case. The short block is then Deck Plate bored and honed to 99.75mm in our in-house Sunnen SV-10. IAG‘s in house honing process is able to set custom piston to wall clearances to best fit your needs. The modified case halves are then assembled using a new 2012+ Subaru 2.5L heat-treated STI crankshaft (or Manley Billet add $1300) that is matched to ACL or King race main bearings. Custom IAG TRI-BEAM +2mm connecting rods by Manley and ARP2000 rod bolts are utilized along with ACL or King race rod bearings. The case halves are sealed with OEM sealant and ARP main bolts. IAG Spec 99.75mm Custom Forged Pistons by Manley with .210 inch wrist pins are chosen to finish the Stage 4 Extreme short block. IAG‘s custom pistons feature a lightweight design while increasing strength where you need it and are designed to work exclusively with the IAG +2mm Tri-Beam connecting rods. The wrist pin is short and is made from strong tool steel. The pin piers are profiled to increase pin boss strut. IAG‘s pistons feature a 25% larger oil ring for reduced oil consumption and added gas ports that aid ring sealing in high boost conditions. Finally, copper wire is installed into the o-ring grooves that adds an additional seal around the combustion chamber.
Stage 4 Extreme Closed Deck Includes:
Additional Options Available:
8.5:1 on D Cylinder Heads (EJ255)
8.2:1 on B, V and W EJ257 Heads with standard thickness gasket.
Head Gasket Recommendations:
*IAG Recommends JE Pro Seal .039 inch head gaskets for B and D casting cylinder heads.
*IAG Recommends Cosworth 1.1mm head gaskets for all V and W casting cylinder heads.
The IAG Stage 4 Extreme Short Block has power output rating of 1000BHP.
*All IAG short blocks are balanced and blueprinted.
Hardware / Seal Option:
Not planning on reusing your original short block service plugs and covers? IAG offers a simple comprehensive cover and seal kit that includes the (3) OEM wrist pin plugs, (3) OEM wrist pin plug washers, (1) OEM separator cover, (6) OEM separator cover bolts, (1) OEM wrist pin service cover, (1) OEM wrist pin service cover O-ring and (2) OEM wrist pin service cover screws. *If you are reusing your original wrist pin service plugs and covers always replace the (3) OEM wrist pin plug washers and (1) wrist pin service cover O-ring before installing a short block to avoid potential leaks.