!00% agree with Griffo and it's not just for GDI engines.
The effect on "regular" engines is that the crankcase gasses enter the inlet manifold and "dilute" the nice clean inlet air thus slightly reducing the potential power output.
By venting the crankcase to air (either with a catch tank or without) you clean up the intake gasses and can more reliably tune the ECU for optimum running.
However, I'm not sure that doing this on later emission controlled cars will not affect the MOT.
Sure they don't do a full sealed chamber emission test and the standard emission test will not pick up the loss of the PCV system but they are supposed to check that the emission control systems are intact.
On later cars, would it show up a fault code of some description.
I thought I read somewhere that the ECU can detect faults in the emission control system. Could be wrong on that though.
