Read a few threads about the cars not fueling correctly with a vent to atmos DV, as the ECU thinks there is more air in the system than there actually is. Surely the difference is very small when you look at the ammount of air going into the engine against the ammount of air released by the DV.

 

This only causes a problem at low loads when the airflow is low therefore it doesn't take much air loss to over-fuel.
As soon as you open the throttle it's fine, driving at steady 60 - 80 mph it starts surging and misfiring if the DTA spring is too light.

 

Also when lifting off the amount of air vented through the DV is a very large proportion of the air entering the engine.
Hence vast overfuelling bangs, pops, flames and perhaps future problems with the exhaust valves and the turbine. But it should be fun

 

that's funny though, it all makes sense but all the damn WRXs here in NZ (and there are as many as in Japan, they all en-up here) run with atmospheric DVs. and without problem. PBM (P Bourne's outfit) even fits them or just a cone filter to the original one on both street and comp cars.

????