Another forced induction vacuum question

[gamefreakgc]

This is true sort-of for a stock N/A engine, for a forced induction set up it's a good idea to pull a little extra vacuum on the crankcase for a better delta across the ring seal and it also helps with windage in the crankcase created by the pistons pushing on the positive pressure caused by blowby. positive crankcase pressure is the enemy in a forced induction rig. this is basically a passive setup. Short of running an external vacuum pump this is the best way of creating system vacuum in the crank case. with this setup you should be able to feel the vacuum at the dipstick hole.

Here's some good reading on it...
Tech: How External Vacuum Pumps Free Up Horsepower - EngineLabs

Isn't also the air intake under a vacuum though at throttle? And it'd be clean air coming in as well.

 

[angus]

Isn't also the air intake under a vacuum though at throttle? And it'd be clean air coming in as well.

It is but not the same.

The PCV system is designed so that at light load and idle the PCV valve uses manifold vacuum to pull out of the right valve cover - at higher throttle angles (i.e. less vacuum) the PCV valve will not have any vacuum but the airflow in the intake "should" compensate by creating vacuum although it won't make that much and not consistently like the intake manifold will.

If you really wanted a catch can, a sealed unit run inline in the PCV hose would be the best - unless, as I said before - the engine has issues.

 

[gamefreakgc]

It is but not the same.

The PCV system is designed so that at light load and idle the PCV valve uses manifold vacuum to pull out of the right valve cover - at higher throttle angles (i.e. less vacuum) the PCV valve will not have any vacuum but the airflow in the intake "should" compensate by creating vacuum although it won't make that much and not consistently like the intake manifold will.

If you really wanted a catch can, a sealed unit run inline in the PCV hose would be the best - unless, as I said before - the engine has issues.

Yeah that's how mine is routed with my supercharger.