• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

Guide to the Volvo PCV system (With video).

^ love this idea. I wonder what the power difference is between venting to atmosphere versus catch can. On one side there is fresh air,but with no vacuum aid. Then dirty air, but lower crank case psi due to vacuum. Anyone ever dyno this?
 
so, all catch cans with a filter on top vent into the atmosphere?
and why would you put a filter on it, or is it when the turbo is spooling it could also draw air in from that point?
 
VQ said:
http://www.pbase.com/stealthfti/pcv

Breather004.jpg


Other Ways to improve PCV breathing.
Click to expand...

Hi,

Can someone tell me where I can get one of these for my 940 2.3 turbo? Many thanks

Martin
 
Negative crankcase pressure

What is the deal with negative crank case pressure. My b230ft runs completely different at idle with an open to atmosphere pathway. I tried to google it and the internet experts that work at dollar tree started to chime in everywhere, so now I am confused...

I first read that the crankcase is supposed to maintain a little negative crankcase pressure so that it sucks oil vapors back into the combustion chamber and if there is no neg pressure maintained, you will burn alot of oil.

Next I read that is completely false, b/c engines used to be open to atmosphere.

The first theory might be true as that restriction nipple we have may give "a little" neg pressure but not alot.

So what is the consensus? Have a catch can that is vented to atmosphere? Keep the restrictor in line somewhere? Please lets pick this one apart... my 740 is an endurance race car and nothing more, and don't want to find out its eating oil or causing problems while at 120.

Thanks,
Shawn
 
Last edited:
sshawn said:
What is the deal with negative crank case pressure.
Click to expand...

New/Rebuilt engines will have negative pressure in crank case.

if there is no neg pressure maintained, you will burn alot of oil.
Click to expand...

On Volvos, with moderate blowby, the engine does not burn that much oil, but dumps it overboard on the ground surface.

Blowby means combustion gases are escaping into crankcase, and this makes the oil "dirty" sooner.
 
I guess my next question is... if there is vacuum, where is the air mass going? Instead of blow-by, would it be... "suck-by" and becoming a part of the combustion stroke?

84B23F said:
the engine does not burn that much oil, but dumps it overboard on the ground surface.
Click to expand...

What do you mean dumps overboard? Due to leaks from engine seals? Vented catch can not catching? Or oil mixed in with the air/fuel and not igniting?

Thanks,
Shawn
 
sshawn said:
...if there is vacuum, where is the air mass going?
Click to expand...

Not if...when piston is moving downward when intake valve is open, it is sucking air...from intake and a pinch from crankcase. It is sucking, and if intake valve-inserts were not installed, that piston would be sucking oil into piston's chamber also. Hence, there is a big suction force when piston is moving downward when intake valve is open.

When rings are wore out, combustion gases pass right thru into crankcase and creates blow-by.

What do you mean dumps overboard?
Click to expand...

On engines with blow-by, its best to not replace seals (unless there is a real issue). When seals are replaced, this increases total crankcase blow-by pressure. And when done, oil will come out of valve-cover cap and via flame-trap and go in to intake hose.

Here, read this post: oil issue from flame trap ,oil separator box.
 
One other thing to consider is that tube off the bottom of the oil seperator that goes down into the crankcase.

The last 3 redblocks I've taken apart all had issues with this thing...it was all twisted up and stopped up. No way oil or vapor was getting through that tube.

Cut the tube short, so there was just enough for the PCV box to sit in, no more problems.
 
propav8r said:
One other thing to consider is that tube off the bottom of the oil seperator that goes down into the crankcase.

The last 3 redblocks I've taken apart all had issues with this thing...it was all twisted up and stopped up. No way oil or vapor was getting through that tube.

Cut the tube short, so there was just enough for the PCV box to sit in, no more problems.
Click to expand...

That. I cut mine off when I was doing oil pump o rings.
 
propav8r said:
One other thing to consider is that tube off the bottom of the oil seperator that goes down into the crankcase.

The last 3 redblocks I've taken apart all had issues with this thing...it was all twisted up and stopped up. No way oil or vapor was getting through that tube.

Cut the tube short, so there was just enough for the PCV box to sit in, no more problems.
Click to expand...

I did this. should I worry about any ill affects not that I really give a **** anyways.
 
84B23F said:
If engine still has negative pressure in crankcase, here comes the dirt/etc.
Click to expand...

Why would dirt come in? Any way you recirculate it, it should be post filter. Even when I just had an open tube, I didn't have any ill effects. Cars used road draft tubes for decades before hydrocarbon emissions became a concern.
 
propav8r said:
Why would dirt come in? Any way you recirculate it, it should be post filter. Even when I just had an open tube, I didn't have any ill effects. Cars used road draft tubes for decades before hydrocarbon emissions became a concern.
Click to expand...

You should see the draft tubes on our morgans, didnt notice one till I took one straight on in the ear when changing the oil a few months ago.
 
You must log in or register to reply here.
Back
Top