I've noticed that the OCC lines on my 07 MCS have a significantly smaller diameter than the stock Valve Cover to intake tube. The stock piece looks to be about 1" or so, while the aftermarket OCC lines are only 3/8". This is a 0.785in^2 cross sectional area compared to a 0.11in^2 area, ultimately resulting on a ~86% decrease in volume. In order for the mass flow rate to be the same (the same volume of air traveling through the PCV hose in a given amount of time), the velocity of the air needs to be increased proportionally. This would require a increase of vacuum/pressure to do this. Anyone else have any thought on this? I see that many of these OCC's that are sold have a way smaller tubing diameter that looks like a big restriction point to me. Just thinking about how changing this parameter might affect the overall dynamics of the intake system and give rise to a rich running condition.

 

the OEM hose is ~3/4" .. replacing it with 1/2" hose did not result in ANY vacuum or boost change..none.

 

Im not saying it would change vacuum or boost, just wondering if it would cause a rich condition since the ECU is expecting a certain amount of air from the pcv system. Not stating anything directly, just wondered if anyone brought this issue up before. Thanks for the feedback though!

 

well my train of thought is: if vacuum doesnt change, the amount of air/flow/pressure/CFM should remain the same no matter what.

*PCV airflow is not monitored by ECU either. It can only read/see manifold pressure & vacuum (if its an N18 it can see oil pressure too). If you have a PCV issue (leak or blockage) the manifold pressure and vacuum pressures are affected..this is what triggers CEL condition for PCV.