IAG Performance S20 Street Cylinder Head PackageIAG 550 S20 STREET CYLINDER HEADS PACKAGE FOR WRX STI FXT LGT > POWER RATING The IAG 550 Cylinder Head Package has a power output rating of 550 BHP ENTRY LEVEL STOCK REPLACEMENT HEADS The IAG 550 Cylinder Heads are designed to function as an entry level replacement for stock OEM heads. If your engine has suffered a catastrophic failure which requires replacement of your cylinder heads, or if you don't have OEM heads to start with, the IAG 550 Cylinder