Twin SU PCV

[SloRolla]

1 hour ago, rebuilder86 said:

nah parrot, the fresh air comes from the air filter housing, the PCV doesnt feed into there, if thats how its setup on urs its been setup wrong.
That little meshed filter is supposed to be stoppign solids from entering the PCV breather hose, which should be on the other side of that. Thats why its inside the filter, so that the fresh air supply is filtered.
The pcv valve wont open from the "at rest" backfiring position unless it has vacuum pulling on it.

To get the catch can to work, you must pull the PCV gasses into it, by sucking through the catch can with vacuum.
If you don't have a vacuum source involved in your catchcan setup, you ompletely wasting your tiare cme and risking having nastys building up in the crankcase, , and greatly increasing oil consumption.
If you want to run a catch can setup it has to be like this
Sorry bout the poor graphics haha MS paint can only do so much

 

I wouldn't need vacuum for the cover breather to work with the catch can? I just have the classic small filter on top and seems to work fine, the can would just catch the engine juice and still supply the motor with fresh air, with one like this. https://www.ebay.com.au/itm/Aluminium-Baffled-Engine-Oil-Catch-Can-2x-AN10-Twin-Port-Breather-Filter-Polishe/272950894232?hash=item3f8d241e98:g:gOsAAOSwFO5aFqTp 

I'll be running the PCV like you did in the diagram. just without the can, AltezzaClub gave me the info I needed to set up that.

Edited December 10, 2017 by SloRolla

[rebuilder86]

ok now I'm totally confused.

hehe

You say your just going to run it without vacuum... then say that ur running PCV without the can.. so wheres the can goibg and whats its purpuse?

[SloRolla]

31 minutes ago, rebuilder86 said:

ok now I'm totally confused.

hehe

You say your just going to run it without vacuum... then say that ur running PCV without the can.. so wheres the can goibg and whats its purpuse?

Sorry about that, I am going to  just tap into the manifold for the pcv, giving it vacuum and also to burn off again. I was thinking of running the PCV to the catch can and not having it to the manifold at all. That's where the can was going to be. But now, I will run the rocker breather to a can and have the PCV not connected at all. So the oil and grease from the breather can be caught somewhere

[parrot]

The catch can will run just fine.

You don't need to over think it

[rebuilder86]

none of this is making sense. haha can u draw a diagram of what your doing?

[rebuilder86]

the manifold must be involved if a pcv valve is to be used, or else there is not enough suction to actually pull the PCV valve plubger from the at rest (or backfire) position. if u are not using manifold vacuum at all, and are sending pcv gasses into the air inlet then there should be no PCV valve involved, this would be similar to a turbo pcv setup. like this.

https://goo.gl/images/5vXjKQ

but this is stupid if its not a turbo as there will not be enough suction in the air intake pipe to pull any nastys out.

 

[altezzaclub]

You don't need to run a PCV valve at all, just take gases from the tappet cover to the air filter.  That allows combustion gases to escape out of the sump and get burnt. There is no reason to have the motor venting to atmosphere in that case, you block the second tappet cover vent.

If you want to run a PCV to actually suck gases out when you accelerate, then you need the second vent to allow air to flow in both directions via the air cleaner. Under acceleration the PCV is open and air flows from the air filter into the motor to replace the gases being sucked into the inlet manifold by the PCV line. When your idling and the inlet vacuum is high then the PCV valve is sucked shut and air flows the opposite way in the other vent, dirty gases go from the motor to the air cleaner. This is just like not having a PCV at all, but at idle there is not much blowby. Under acceleration you have maximum blowby and the PCV system is designed to catch that.

Jeremy that turbo diagram could do with more labels, I don't know if their PCV valve port is actually screwed into the inlet manifold, as that wouldn't work. Without a vacuum in the inlet manifold you can't suck the gases out of the motor, and I assume you don't get a vacuum in the inlet with a turbo.

 

 

[rebuilder86]

yeh it is a shit diagram actually, just the only one i could find.

ok at idle, the atd pcv valve doesnt completely shut, it is a restricted leak at this point but still pulls to create negative pressure required in the crankcase.

this wont happen if u juat run a pipe to the intake near the air filter in a N/A car as vacuum is quickly diminished at low rpm by the amount of air supplied in the area near the filter.

I learned an NA car needs vacuum applied to the crankcase or else the compression rings jump off their seats momentarily at the bottom of the intake stroke while in any power on scenario.

There is not enough vacuum at idle or during power near the air filter. it should be a source of fresh air only.

turbo is a different story.

[rebuilder86]

i think the only way u could really settle this is with a dyno test.

one with the pcv valve attached to the manifold (so that the air leak os the same in both tests) but the crankcase left to vent

and one with the pcv in the rocker cover actively pulling like its designed to.

put it this way.

without a vacuum pcv system, the crankcase can at times be greater than atmospheric preasure, and this is bad. with the pcv functioning as designed, with or without a catchcan between the valve and intake, there will always be negative pressure on the crankcase and this will stop backwards blowby up the fresh air supply hose.

the only times it continues to fail and blow oil back up the fresh air line is on decceleration, and this is where i think the whole system is flawed. plus the little bit of loss of good atomising air flow through the venturi for a given rpm due to the induced vacuum leak.

Edited December 12, 2017 by rebuilder86

[altezzaclub]

"ok at idle, the atd pcv valve doesnt completely shut, it is a restricted leak at this point but still pulls to create negative pressure required in the crankcase."

I thought they closed up as the high inlet vacuum at idle sucked the valve closed against the spring. So at idle you still shouldn't have blowby going into the air cleaner through the vent pipe.

In deceleration it should be the similar, high inlet vacuum the same as idle, small amounts of blowby being produced, so it should suck the crankcase clean if its a restricted leak.

Either way, I'm sure the difference won't show up on a dyno!

[rebuilder86]

it does close but not completely. blow through the pcv valve in the direction of flow and ull find it restrictive but not blocked.

this is so that at idle the pxv hose still pulls air out of the cranccase and this is replenished by the air coming from the pipe which goes to the air intake.

1 hour ago, altezzaclub said:

So at idle you still shouldn't have blowby going into the air cleaner through the vent pipe.

this point suggests u may not be 100% on the function of the pipe to the air cleaner. 

u should never have blowby going to the air cleaner, its desigbed to flow away from the air cleaner into the rocker cover  to replenish the air air sucked out by the pcv valve, as per my diagram. 

 

there are 2 seperate functions of the entire system

1. to remove excess pressure and maintain a slightly negative pressure in the crankcase

2. to remove contaminents from the crankcase before they settle into the oil.

If u simply ran an atmospheric vent, number 2 wouldnt happen.

if u ran the system without the manifold suction, number 1 wouldnt happen at high rpm.

[altezzaclub]

"his point suggests u may not be 100% on the function of the pipe to the air cleaner. "

Fair enough-  That galv airbox I had made always has a little oil & condensation water in the bottom seam, so vapour on mine does go from the tappet cover back to the air cleaner. I figured all of the PCV valves worked like that, but either mine is crook or it doesn't suck enough at idle to keep the crankcase at negative presure.

The 4AGEs don't have a PCV valve at all. There is a fixed port into the inlet manifold with a hose from the tappet cover and that's all.

I'm looking forward to making a dry-sump setup for the rally car,  then we have some serious vacuum on the crankcase. That one I will dyno for the difference!

[rebuilder86]

so long as you have a functioning PCV valve your problem is most likely at hard deceleration.
AT hard deceleration, the rpm is fast, but the manifold suction is high, so the PCV valve is closed, and the crankcase becomes a constantly variable pressure pump, and that pressure goes in and out of the breather pipe. Its a good idea to also put a catch can (closed with no filters on it, one line in one line out) in line on this pipe for this very reason.
I'm currently employed working on a system for turbochargers to overcome this issue.
involves vacuum pumps! ask no more.

[rebuilder86]

6 hours ago, altezzaclub said:

The 4AGEs don't have a PCV valve at all. There is a fixed port into the inlet manifold with a hose from the tappet cover and that's all.

yep and thats because it was designed to also work with a supercharger!! (4A-GZE)
In place of a valve, it has a very small opening, the fact that the engine is fuel injected makes a pcv valve less important, as the injectors can be controlled to give more fuel during the idle scenario where vacuum is lost to the PCV leak. saying that, its not ideal, but they just have to have it. These setups are even more notorious for grim all over the throttle plate, because when under boost, it jsut throws pressure through that orifice into the crankcase and back out the breather pipe and all over the throttle plate.

horrible and stupid right?
Well if they had put a PCV valve in it, the valve would last not very long due to the constant pressure slamming the PCV vaalve tumbler seat back against the backfire seat face and this would stop all ventilation as the case would be closed! so the best option is to just throw it all into the throttle body up the fresh air tube.
Again, it can be minimised with catch cans on the fresh air tube to catch any nasty backflowing gasses with oil and gunk in it.