VTC_CiViC

Ok with all the talk about PCV's in here latley, I got my squirles running around in my head and I thought of something, but first I need a little clarification. I've never been teribly "up" on the exact layout of Honda's PCV system. I know the black box is fed pressure though the large hold in the block where it sits, then up through the baffles to seperate liquified oil and up through the small vacuum tube and valve back into the intake mani. Now here are my two questions:

1. The above layout is true for my SOHC's, but I noticed my GSR has a second vacuum tube on the top of the black box going to a brass port on the back of the block (not the head).. why?

2. Is the pressure within the crankcase enough to force blowby out of the PCV box (I assume yes) therefore negating the need for any kind of draw through assistance, so one could basically just run the top vaccum hose straight to a cannister/collector rather than back to the manifold?

Extra Credit:

Assuming you couldn't evacuate the pressure in the crank suffieciently through the PCV, the pressure would force it's way up through the valve cover and out of the valve cover breather no?


TIA..... and the squirles keep turning

dasher

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VTC_resurected_CiViC &raquo;</TD></TR><TR><TD CLASS="quote">
1. The above layout is true for my SOHC's, but I noticed my GSR has a second vacuum tube on the top of the black box going to a brass port on the back of the block (not the head).. why?</TD></TR></TABLE>

Most likely to provide an alternative route for crankcase pressure to enter the PCV black box if the large lower port is blocked temporarily by oil.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VTC_resurected_CiViC &raquo;</TD></TR><TR><TD CLASS="quote">
2. Is the pressure within the crankcase enough to force blowby out of the PCV box (I assume yes) therefore negating the need for any kind of draw through assistance, so one could basically just run the top vacuum hose straight to a cannister/collector rather than back to the manifold?</TD></TR></TABLE>

Yes, the pressure in the crankcase is enough to force blowby through the PCV line without the assistance of vacuum, especially in turbocharged engines where their is more blowby present. You could simply route the PCV line to the catch-can if so inclined.

A few things to keep in mind:

1) The crankcase pressure will choose to free itself in the most efficient way possible. This means that if you have an extremely inefficient Crankcase evacuation setup on your block most of the pressure will choose to be evacuated through your valve cover breather instead. Personally, I prefer to remove these dirty gases as quickly as possible rather than have them contaminate the head/valve-train with excessive blowby being introduced to the head.

2) Even though the crankcase pressure is enough to free itself without the aid of vacuum, it does so inefficiently and at the cost of increased windage and contamination. Vacuum assistance to evacuate the crankcase will free up horsepower and keep your oil/engine healthier, longer.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VTC_resurected_CiViC &raquo;</TD></TR><TR><TD CLASS="quote">
Extra Credit:

Assuming you couldn't evacuate the pressure in the crank sufficiently through the PCV, the pressure would force it's way up through the valve cover and out of the valve cover breather no?</TD></TR></TABLE>


Yes, and this happens normally on a stock NA honda engine at moderate to high loads anyways.

Tests for proof:
https://honda-tech.com/zerothread?id=697498

dasher

I'm really getting sick of all these PCV threads also..... but at least your thread introduced 1 new question I've come accross in all the years with question # 1(the rest of it is old news).

VTC_CiViC

Excellent

I noticed something in that PCV write-up with regards to the actual PCV valve. I see that the valve is progressive with regards to load and how it opens, but from what I understood, as atmosphereic pressure increases (from vaccum to atmo.) the valve opens more to assist in evacuating blowby, however, how does this work with positive manifold pressure? By simply following that train of though it would appear as if the PCV would remain open during boost and charge the crankcase full of pressurized mixture which in conjunction with natural blowby would equal alot of bad things going on down there. Where in this line of thought did I go wrong?

dasher

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VTC_resurected_CiViC &raquo;</TD></TR><TR><TD CLASS="quote">Excellent

I noticed something in that PCV write-up with regards to the actual PCV valve. I see that the valve is progressive with regards to load and how it opens, but from what I understood, as atmosphereic pressure increases (from vaccum to atmo.) the valve opens more to assist in evacuating blowby, however, how does this work with positive manifold pressure? By simply following that train of though it would appear as if the PCV would remain open during boost and charge the crankcase full of pressurized mixture which in conjunction with natural blowby would equal alot of bad things going on down there. Where in this line of thought did I go wrong?</TD></TR></TABLE>

I'm getting sick of posting this info for the 546135473 time, but here it is again:

This is the way the PCV valve functions:

engine off/backfire --- Low load/Idle --- Medium Load/cruising --- High load/WOT
0/positive pressure---Highest Vacuum--- SLIGHT Vacuum ---- almost 0 Vacuum
PCV Valve closed ---- PCV open slightly-- Valve opens more --- Open all the way

.... So you want to look at the first column under boost conditions(positive pressure) and you will see that the PCV valve will close.

Turbowa

Sorry but I have to chime in on this. I've read almost all the post and there all very informative. BUT there almost all on the D and B series witch have the black box on the back of the engine. Well, mine is the F series (F23a1), 99" accord witch has no black box or a place on the back of the block to tap in to, to vent. Tho only possible place that I've even found as a remote possibility would be to put a nipple in the bolt were the stay hole for the back balancer shaft is. You could get a small fitting in there and vent the crank case directly and not interfer with the balancer shafts. Right now I took the stock PCV valve out and run a line from the valve cover breather and old PCV valve opening together into a catch can and another line into the intake (air filter adapter) before the turbo. So I guess the question is are the 2 vents in the valve cover enough or should I try and tap into the back of the block? I have no big freeze plugs like the D and B series to use. All of the ones on the F23 are for coolant.

dasher

If you are going turbo on that F series i would tap 3 lines out of the valve cover. Or you could tap the block if you know what you are doing.

Turbowa

Cool, thanks. I'll try and see if I can find a nippled fitting for that bolt hole.