From APS website..

http://www.airpowersystems.com.au/wrx/blow.htm

"The large primary vent is designed to plumb back to the standard entry point which ensures the best driveability during cruise conditions and cures the erratic idle and engine's rich condition (on gear changes) problems seen with after market external single venting blow off valves."

I thought this was a VTA dump valve, but it seems to imply that it's a recirc in this section. All new to me this MAF/Dump valve stuff, so can anyone explain.


And I'm not trying to start the usual 'Chav' psssttchhhh debate - I really do want to know

 

Probably a two stage combo recirc/vta lump of junk.

It means your wasting your money and better off sticking with the standard one and spending your money on something advantageous like power/handling/braking/ICE mods