[Homemade WRX]

^^^^the FA20 is a completely different engine from the EJ, so I wouldn't start to speculate. Add that and the fact that direct injection leaves room for more power over port injection; I'm curious to see what head room was left in the engine from the factory. If you've ever tuned or built Subaru's from and engineers approach, you will know there is lots left on the table because of the factory tuning 'around' emissions.


glad to see someone else knowing what a stepped manifold is, however in the US the steeped feature, we just consider to be part of the 'primary' section of a manifold.

for those who don't know, a step is nothing more than the first section of the manifold that is the same ID as the port. It is usually kept short and then 'steps' into a larger ID tube in the primary...with a hard lip. This lip acts as an anit-reversion device. Then the primaries will come into a collect or go into secondaries (tri-y).

As a performance and emissions enigneer, the factory usually leaves a decent amount on the table because of budget and tuning for emissions.