Andy
03-25-2011, 08:53 PM
I see allot of talk lately about catch-cans and vacuum pumps. I decided to touch on the subject a little.
In factory form, the crankcase has 2 holes to the atmosphere. One has a PCV valve on it and the other is open. Basically what happens is that engine vacuum sucks air through the pcv valve and the vent next to the oil cap is what allows air to travel through the crankcase. The reason for this is that you never want to pressurize the crankcase as it will blow out gaskets and hurt performance. Ideally you want some vacuum or no vacuum at all but never pressure.
With boosted applications, air cannot be sucked through the pcv valve because the manifold is pressurized. In addition to that, pressurized cylinders will leak some boost past the gap in the piston rings into the crankcase. Since you are pressurizing the crankcase, you need to get that air back out otherwise it will begin to blow out of the breather next to the oil cap. The best method for doing this is with a vacuum pump. So here is the scenario.
1. Eliminate the pcv valve and run a hose from where the pcv valve was to a catch-can and then from a catch can to a vacuum pump and from the vacuum pump into the atmosphere. This will maintain a vacuum on the crankcase preventing it from pressurizing and also preventing oil from spewing out of the breather next to the oil cap. Make sure that the breather has a filter on it as that is where the air will be sucked in. On my particular combo, that breather is gone and I have a breather on the valve-cover.
I hope this helps and makes sense. Anyone running a boosted application should consider this mod.
This site will help explain it further.
http://www.gzmotorsports.com/street-pump-kits.html
In factory form, the crankcase has 2 holes to the atmosphere. One has a PCV valve on it and the other is open. Basically what happens is that engine vacuum sucks air through the pcv valve and the vent next to the oil cap is what allows air to travel through the crankcase. The reason for this is that you never want to pressurize the crankcase as it will blow out gaskets and hurt performance. Ideally you want some vacuum or no vacuum at all but never pressure.
With boosted applications, air cannot be sucked through the pcv valve because the manifold is pressurized. In addition to that, pressurized cylinders will leak some boost past the gap in the piston rings into the crankcase. Since you are pressurizing the crankcase, you need to get that air back out otherwise it will begin to blow out of the breather next to the oil cap. The best method for doing this is with a vacuum pump. So here is the scenario.
1. Eliminate the pcv valve and run a hose from where the pcv valve was to a catch-can and then from a catch can to a vacuum pump and from the vacuum pump into the atmosphere. This will maintain a vacuum on the crankcase preventing it from pressurizing and also preventing oil from spewing out of the breather next to the oil cap. Make sure that the breather has a filter on it as that is where the air will be sucked in. On my particular combo, that breather is gone and I have a breather on the valve-cover.
I hope this helps and makes sense. Anyone running a boosted application should consider this mod.
This site will help explain it further.
http://www.gzmotorsports.com/street-pump-kits.html