Killer B Motorsport 4-1 Holy Header Exhaust Manifold 2 Bolt 2002-2014 WRX / 2004-2021 STI

The Killer B Motorsport Holy Header was developed using state of the art CAD software & simulations to determine optimal design to increase power as much as possible throughout the rev range. Short as possible primaries with a single secondary significantly decrease header volume allowing exhaust gas pressure to build quickly. Symmetrical 4-1 design maintains high and consistent exhaust velocity as RPMs rise. You can expect faster spool up time compared to long primary/double secondary designs. A difference you will immediately notice in throttle/boost response and the ability to hold more power higher into the revs. Cast Collector. The collector is thick walled cast 347 (321) stainless. The casting removes several welds, each weld removed is one less flow disruption (reduced turbulence). The casting has features milled into it that assure the primary tubes fit VERY concentric every time. Using a casting allows the collector to be designed as a true high velocity merge vs tubing t