For anyone running pcv block off plates/catch can set ups or knows alot about our pcv

[Savir04]

Hi there, this is a continuation of another thread i got going on, but this is a whole different discussion so i figured id make a thread on this.

The original thread is here http://golfmkv.com/forums/showthread.php?t=159156

I left off with saying how i was going to provide detailed information on our pcv system, I will update that thread as soon as i get this clear on this thread....

My bad for not replying, i've been super tied up and havent had time to reply

Well i was going to make digrams and what knot explaining how the pcv system works in detail but ima skip all that assuming ya'll know exacly how it works...however, ill post up some good informative pcv system goodies upon anyones request.

This following argument is by no means intended to be hostile in any way, this post is all peace and love mahn.

So at this point i have one question...in an after market catch can setup, while the engine is under vacumm only, where does the pcv system obtain the necessary vacum to vent/guide blow by out of the head/crank case?...All after market catch cans ive seen completly remove the front pcv unit and replace it with a block off plate..thus removing the connection between the intake manifold and the pcv system...this means the only source of vacum the pcv system would see is from the rear breather hose connected to the turbo inlet...and the only time the system will see vacum from there is when the is engine under load, which is when the turbo is boosting and sucking mad air from the inlet pipe thus creating vacum in the breather hose....idk if i'am overthinking it, but that can't be good

Vw invested a whole lot of money and time into development for this engine, and i cant justify how it's fine to just remove the only source of vacum the pcv system sees when the engine is NOT under boost...the system is designed so that when the intake manifold is under vacum; it literally SUCKs all the blow by that collects in the valve cover from both the crankcase and head....when running a block off plate, and the engine is under vacum, there is nowhere near enough vacum generated in the turbo inlet to perform the same task the front OEM pcv setup performs...on idle the intake manifold will generate 20hg of vacum while the turbo inlet will generate close to zero hg's of vacum...that's a big difference...it is very clear that vw realized this and saw a problem with using only the vacum generated in the turbo inlet as it's not enough to "suck" / "guide" out blow by while the engine is off boost, that's why they added the front pcv unit connection to the intake manifold, so the pcv system recieves sufficient vacum from the intake manifold while the turbo system is off boost...my theory for VW's reasoning behind this overexcessive requirment of vacum is as follows,..blow by pressure from both the head and crankcase collect in a chamber molded inside the valve cover, this blow by pressure needs to be "sucked" out rather than "pushed" out like on any typical N/A or boosted engine...the 20hg's of vacum genarated in the intake manifold "sucks/guides" out the blow by gases/pressure collected in the chamber molded inside the valve cover when the engine is off boost...when the engine is on boost, the front pcv system is closed/blocked by the front pcv check valve and in this instance vacum generated in the turbo inlet is what "sucks/guides" out all the blow by gasses/pressure......in both instances there is always a strong amount of vacum present in the head; sucking/guiding the blow by out of the valve cover...so like i said, it is clear that for the pcv system to function properly it neeeds to see adaquete vacum while the engine is NOT under load...

I honestly dont see why it would be bad to just let the blow by vent itself out with its own pressure like its done on most engines, but vw clearly sees a problem with that judging by how they designed the pcv system...i kno on most N/A engines and some turbo engines its safe to let it vent with its own pressure without having excess pressure build up in the head, but vw clearly saw a problem with that on our specific engines...i think the problem is that the pcv set up on our engines does not flow free enough to allow blowby from the head and crankcase to vent itself out completly without creating excess pressure in the head, thats why they designed our pcv system in a way that the vacum generated in the intake manifold aids in pulling out the blow by/pressure out of the head...the main thing in mind here is "excess pressure build up in both the head and crankcase"...thats whats trying to be avoided here....also the vacum in the intake manifold is what "guides" the blowby gasses out of the head...if vacum was not present, all the gases/pressure would randomly flow throught the entire head until they eventually find theyre way out...which cant be good

So now, why do after market catch can makers think it is ok to remove the only source of strong vacum the pcv system see's while the engine is NOT under load?...when the engine is under boost the catch cans dont really change anything in the way the pcv system was ment to function, but when the engine is under vacum the catch can set ups completly fuck up the way the pcv system was ment to work....like i said im just trying to educate myself and maybe contribute to helping others understand the pcv system, im not bashing anyone at all by any means, im just curious because im designing a pcv catch can set up that will retain oem functionality (using vacum from the intake manifold to guide/suck out blow by gasses), remove all the crap that goes into our intake valves, and that is trully bullet proof...and im really close but maybe im missing something here, becuase i cant figure out how it is "ok" to remove the functionality of the front pcv valve, reroute everything to the rear with a block off plate, and just slap on a catch can that leads to the rear breather hose...how does the blow by/gasses guide itself out when the engine is under vacum with a catch can? i mean the system was design how its design for valid reasons...how is the vacum generated in the turbo inlet enough to "suck" out this blow by out of the valve cover when the engine is NOT under boost?...in this instance the vacum generated in the turbo inlet is nowhere near the 20hgs of vacum pull found in the intake manifold...the 20hg of vacum that according to vw is neccesary to guide/pull out those gasses/pressure....any help lol? Sorry about the ubber long post.

[Cadbury]

There may be no/little vacuum at the rear port at idle but there is probably less pressure than there is inside the crank case. With this scenario the gases will be drawn to the lower pressure.

An under hood sniffer test is done when some emission tests are performed on a car. Using just the rear port there is a chance some of the blow by gasses will make it past the air filter and into the engine compartment, this would cause the test to fail.

VW knew this and this is probably why the front port is there, so at idle there is no chance for the gasses to make their way into the engine compartment.


-Cad

[BSH Speedshop]

Originally Posted by Cadbury

There may be no/little vacuum at the rear port at idle but there is probably less pressure than there is inside the crank case. With this scenario the gases will be drawn to the lower pressure.

An under hood sniffer test is done when some emission tests are performed on a car. Using just the rear port there is a chance some of the blow by gasses will make it past the air filter and into the engine compartment, this would cause the test to fail.

VW knew this and this is probably why the front port is there, so at idle there is no chance for the gasses to make their way into the engine compartment.


-Cad

There is definitely less pressure in the rear port than the crank case. Otherwise a perfect statement.

[Savir04]

Well i guess there goes my double catch can design, lol, i was overthinking it way too much....thnx for the reply dan, it was a perfect answer, it was the bit of information i was missing....i kinda figured that out myself but i wasent too sure...and thnx bsh for stoping by and confirming...the catch can/block off plate you guys offer as well as other vendors offer is definatly the best solution out there...

one more thing thou...i was speaking to a shop and they said that the oem pcv system provides a lubrication property to our engines...they said its responsible for lubricating certain areas in the turbo system and in the head...valve seats, throttle body valve, DV, wastegate, piping seals, turbo fins, turbo shaft seals, ect....he said it was a bad idea to catch can the system and thus remove this lubrication property the oem pcv system provides...

I think he brought up a good point, but then he failed...he said some statements that really put me to question if he really knows anything hes talking about...he said

1.putting an only vacum block off plate with a catch can is bad because it removes oil in places the engine neeeds, however if you run a catch-can-vent-to-atmosphere-set up this will not be a problem....this is why we only do vent to atmosphere set ups here...

My reply was, as far as lubricating the engine, there is absolutly no difference in a catch can recirculating set up vs catch can vent to atmosphere, if anything a vent to atmosphere set up would completly elliminate any oil in the system vs a recirculating set up...he clearly got owned but still went on making himself look even dumber

2. He argued that there is no chamber in the valve cover where gasses from the head and the crankcase combine to be vented

Owned him again by shwoing him pictures and diagrams clearly showing a molded chamber inside the valve cover.

3.he argued that there is no molded passage on the valve cover that leads from the front of the head towards the rear breather port.

I tripple owned him on this one...there is a sealed passage molded inside the valve cover that leads from the front of the valve cover to the rear port....if im not mistaking, the molded route goes right thru the coil pack inlet sitting on top of cylinder # 2

4.he said that the oem front pcv only has one valve

I explained that the front pcv unit has 3 valves, one master check valve and 2 no return valves...the master check valve blocks boost and the 2 no return valves are responsible for rerouting blow by to the rear while the engine is on boost....he failed to agree...

5.he Said that the pcv system was only for pressure build up in the head, that the crankcase does not produce blow by.

I didnt even reply on this one, At this point i just thanked him and left....

So despite the misinformation he provided he did bring up a good point about catch cans elliminating the lubrication propertied the oem pcv system provides, is this true? And is it something worth being concerned about?

[BSH Speedshop]

I think you know what the right answer is without further input or comment on the info you were given. If we can be of any assistance going forward, feel free to reach out.