dawes and needle valve for common rail?

[nipagu7]

when the car is on boost and you then take your foot off the throttle , the pressure blow back in the air intake carries engine blowby gasses back past the MAF sensor , after a while this builds up on the MAF sensor and causes it to give false readings . A catchcan greatly cleans up the blowby gasses which in turn keeps the MAF sensor cleaner longer . although it is still advisable to occasionable clean the MAF sensor with MAF sensor cleaner spray occasionally ( i do mine when i do oil changes ) . if the egr is not blocked the catch can does go someway towards helping keep the inlet manifold and valve intake ports clean , as the blowby gasses combine with the egr gasses to stick and clog them up .
if you block the egr it would stop the crud buildup occurring in the first place , and most people would get better fuel economy and more power although you may need to look at a dawse and needle valve arrangement to help control the turbo , which has benifits of allowing higher boost ( more Power ) and better driveability ( more power at lower RPMs )