Post by
Margus »
https://forums.nicoclub.com/margus-u138824.html
Mon Mar 30, 2015 4:17 pm
Hi.
You have all got it a bit wrong.
Venting air through the PCV valve to your intake, only circulates fresh air in your valve covers. Fresh air goes in to the ex.side, and gets sucked out through the intake side, to the intake manifold. The crankcase gets absolutely no fresh air circulation of what so ever. Clean air will never enter there, because there is no vacuum. Only pressure, that gets reliefed through the metal 90degree pipe.
If this pipe is blocked, under boost blowby will force air out through the internal oil return lines. Causing no oil return to the sump, and we all know what happens next. First, oil pump gets dry (common bearing failure), then oil gets pushed out through the valve cover vent holes. Enters your intake piping, next it enters intake manifold and now you have a nice detonation that kills your pistons (common failure).
To prevent it.
Crankcase is not vented, because there is only one (exit) venting point (90degree metal pipe). To vent it, you have to make another venting point, and leave it open in the atmosphere connected with catch can and filter. Then connect original venting point straight to the intake using PCV valve. (yes you can use catch can there, but not necessary).
But under boost all changes. PCV closes, and if blowby occurs, it gets vented out through the seccondary venting point into the catch can and then in atmosph. All goooood but...
Too complicated? yes.
The best and the far easyest way to vent your motor, is to replace the 90degree narrow metal pipe, with bigger one, and connect it to the catch can, and thats it!
There is no need to vent your valve covers into intake with PCV (but you can). Just put filters on both side.
If crankcase venting pipe is big enough, there is no oil return problems from head.
Hope that helps.
Margus