IAG Performance Stage 4 Cylinder Head Package w/ GSC +1mm Valves and S2 Cams 2018-2019 STI Type RA N25 Heads

IAG's Stage 4 Cylinder Head Package utilizes a CNC porting program for the WRX STI heads that was developed over the past five years and tested on the most successful high-horsepower Subaru's. The ported head package starts with brand new WRX STI OEM head castings directly from Subaru of America. The bare castings are visually inspected then fixtured into our in-house Centroid 5-axis CNC Machine, one of the most advanced precision engine machining equipment in the world. The Centroid CNC ports the intake and hard to reach exhaust "dog-leg" port runner. The benefit of CNC porting is not only an efficient way of machining the heads it also offers consistent port results that are hard to achieve by hand. Once the Centroid completes the port process the heads undergo a cam clearance machining process that removes material from the lifter area where large duration cam profiles are known to contact the castings. Short after the heads are drilled to fit larger 1/2" or 14mm head studs which are commonly used in high horsepower builds. Next, the OEM guides are pressed out and replaced in favor of GSC Manganese-Bronze valve guides that are shaped to improve airflow. Once all the new intake and exhaust guides are in place they are diamond-honed in our honing station. The heads are then fixtured in our Serdi 3.0 Valve Guide and Seat Machine to cut all intake and exhaust seats with a multi-angle valve job that suits the flow characteristics of GSC's +1mm valves. At this point, the heads decks are resurfaced using our TS-3000 BlockMate that cuts the aluminum to a smooth even finish. After resurfacing, the heads are ultrasonically cleaned to remove debris and oils from the machining process. The heads are then reassembled using your choice of GSC Billet S2 or S3 camshafts. The Stage 2 cams are intended for vehicles making 500-700 wheel horsepower while the Stage 3's are for drag racing applications intending to make 750-1000 wheel horsepower. During the final assembly, the cams are matched to IAG-Spec Beehive Valve Springs and Retainers along with GSC Viton stem seals then bench-lashed to a tolerance that is close to final specifications.


Stage 4 Ported Head Package Includes:

• (x2) Brand New Subaru OEM Cylinder Head Castings
• (x8) GSC 37mm (+1mm) Intake Valves
• (x8) GSC 33mm (+1mm) SuperAlloy Exhaust Valves
• (x16) IAG-Spec Beehive Springs & Retainers
• (x16) GSC Manganese-Bronze Valve Guides
• (x16) GSC Valve Stem Seals
• (x16) OEM Lifter Buckets
• Your choice of GSC S2 or GSC S3 Billet Camshafts
• IAG Performance CNC Porting
• Multi-Angle Valve Job
• Drilling for compatibility with ½" or 14mm Head Studs
• Machined Cam Lobe Clearance
• Resurface
• Ultrasonic Cleaning
• Bench Lashed

GSC W25 & N25 Camshaft Specs:(2008-20 STI / 2018-20 STI Type RA / 2019 STI)
S2 Billet Cam is intended for 500-700WHP

S3 Billet Cam is intended for 750-1000WHP

Recommendations / Warranty:

• Final lash will need to be set upon the long blocks assembly.
• Assembly and professional installation recommended.
• Workmanship/parts warranty will only be available for professionally installed cylinder heads.