tekka01

::Warning:: somewhat long post ahead

I just got my krank vents not too long ago, and I'm planning on doing a catch can install along with them. I have one concern though before I do all this...since the front krank vent on the breather now only allows flow away from the valve cover, I was wondering if it would be smart to insert the krank vent between the breather and the stock airbox, or instead, do one of the two things in the illustrations below instead.

1) T the line coming from the pcv and breather together (since both now flow away from the valve cover) ->catch can ->krank vent -> intake manifold


2) front breather -> krankvent ->vent to atmosphere; pcv->catch can ->krank vent->intake manifold


My main concern is that since the front breather now flows away from the valve cover, that blowby will escape into the intake if I just leave it routed to the stock airbox. Let me know your opinions please, I just want to make sure I'm doing this right.

SpitfireS

IMO option #1 is not good because you want the crank case to be able to release pressure at all times, even when the intake manifold is not sucking (IOW doens't have a lower pressure then the crank case)
Release it filtered into the atmosphere (as in option #2) or into the stock airbox (OEM ).

fperra

The first picture won't flow any blowby under boost. It would be the same as sealing the front valve cover vent. The second picture is how mine is set up, but instead of a breather you could pipe it back to the intake before the throttle body.

tekka01

by keeping it oem, and piping the line back to the intake after the krankvent, is my concern of blowby getting into the intake false? I'm having a hard time understanding this since the front krankvent only allows flow away from the valve cover, wouldn't this mean that more blowby could get through the front? Sorry for the dumb questions

SpitfireS

tekka01 Posted on Feb 1 2007, 11:19 PM
No, that is not false, it is correct.
But it is NO CONCERN as it was designed to be that way.

In the unmodified OEM situation, the front intake, the one without any kind of valve, has a dual purpose.

#1 - When the pressure in the intake manifold is lower then in the crank case, caused by a closed throttle valve while the engine is revving, there is a flow towards the intake manifold, but no (or very very little) vacuum is created because there is filtered air, coming from the black rubber intake pipe between air filter and TB where there isnt's a low pressure as it is before the TB, flowing into the crank case through the forward intake.

#2 - When the perssure in the intake manifold is higher then or equal to the pressure in the crank case the OEM PCV valve is closed, any pressure build-up in the crank case caused by blowby is then released into the black rubber intake pipe between air filter and TB.

With both Krank Vents installed correctly #1 changes.
(That's why you bought the damn things in the first place )
The forward Krank Vent does not allow flow into the crank case anymore.
Period.
The lower pressure in the intake manifold starts to create a vacuum (or as low as the pressure in the intake manifold is) in the crank case.
Once the pressure is equal the Krank Vent inline with the OEM PCV valve is closed maintaining the vacuum in the crank case.
Until there is blowby again.

With both Krank Vents installed correctly #2 changes only in a small detail.
The blowby has to open the Krank Vent to release the pressure build-up.
The Krank Vents need very little pressure to open so that is no concern.

tekka01

great info....thanks a bunch for all your help!