So just had my engine rebuilt and started it today! So far so good.

Spec: 2003 evo 8 rebuilt engine, Manley rods, weisco pistons, kelford 272's, buscher 20G.

vac at idle is about 10-12 - doesn't appear to have an vac leaks.

so while the engine is running, I raised the throttle just gradually and the BOV is opening. The vac hose is connected to the intake manifold, and I took it apart and it has the white spring inside. Any ideas why this is happening.

 

What spring is in it?

Is it a Q or older 50mm?

 

Appears to be an 8 PSI ~

 

The OEM BOVs ARE open when the engine is idling.

So if an aftermarket one is going to perform as well as a stock one, it should be open too.

 

check the spring

 

The low vaccum at idle is caused by valve over lap from cams. Normal.

The bov is opened with vaccum. So when part throttle there is still vaccum so it will be somewhat open. Since the engine has part vaccum at part throttle.

 

It's just bad tuning. Vac at idle should be 18 to 20 inches. Only a bit less with wild cams.