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Understanding the MK7 PCV function, retrofitting the MK8 PCV, and why catch cans are bullshit(IMO)

tigeo

Autocross Champion
I'm not familiar with how it transitions into the turbo.

Basically the main difference between the Epman or Unitronic TIPs (which hurt vacuum, but not completely throwing it out the window like the BMS did) is that they have a smooth transition into the compressor housing. Whereas the BMS (and the CTS V2 which tested very low peak TIP vacuum levels with a gauge).

I don't think that vacuum level is directly correlated to airflow but moreso the port location and transition into the compressor housing. I PREDICT that the parts with a large dia and then necks down into the compressor (with the PCV on the large diameter portion) are more likely to give less vacuum on the TIP.

Look at Jeff's testing of outright flow on the things I've at least gotten TIP vacuum levels on...

https://mygolfmk7.com/turbo-inlet-pipe/

View attachment 299436

It goes Stock > APR > CTS Cast (V2) > BMS in order of flow.

Based on this (which was determined that the gauge is pretty damn close to accurate with all OTHER configurations later on when I fitted the PCV sensor):

https://www.datadrivenmqb.com/drivetrain/venturicrankcasetesting

View attachment 299437

The most the CTS V2 (granted, with an intake as well) ever pulled was -0.48psi at it's peak. Based on the difference of me testing with OEM TIP + airbox vs OEM TIP bare (with no filter or tube or anything), there could be another 0.6psi of negative pressure AT THE MOST. So we'll call it -1psi at best.

Whereas the Unitronic pulled -1.8psi at peak, and the Epman pulled -2.2psi at it's peak.


Obviously this is a bit of a stretch, assuming APR = Epman... but in order of vacuum:

Stock > Epman/APR > Unitronic > CTS Cast (V2)

So the CTS flows less than the Unitronic, AND produces less vacuum.


And of course people on the FB pages and stuff are acting like the sky is falling as predicted. Bottom line for anyone not tracking their cars, this will largely never show up as a real problem. Just wanted to make people aware of how to go about fixing their problems... rather than throwing junk PCV plates at them.
Let the peasants eat cake. Where are they losing their minds?
 

DerHase

Autocross Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
Let the peasants eat cake. Where are they losing their minds?

People all concerned about needing to change their TIPs on cars that don't see track.

And PMs (on FB) from people who "I've been running x TIP and never had problems with it"... like yeah. Driving in a straight line isn't as stressful on the PCV as tracking. By a long shot.


Like... I mentioned it multiple times that actual "problems" are almost never going to be experienced on the street. Unless you have actual tangible problems... your setup could be "less than ideal" but don't worry about it. Even the OEM system blips into positive pressure for a split second taking off from stops.

Is it great? No.

Now if you're putting actual pressure on the crankcase during a pull... I suspect bigger turbos/crazy boost MIGHT actually increase in crankcase pressure if the amount of blowby exceeds the additional airflow of the turbo suctioning on the PCV system.

But if it balances out to at least "not positive" in the meat of the pull, it's probably fine "enough" on the street. Hell, @Diggs24 has been on the MK8 basic retrofit for a few months now.

Doing the full retrofit is NOT meant for people who want to extract every single last horsepower from their car on the edge of reliability. Adding WGDC isn't the way to do that. If choosing a new (hybrid) turbo, I DO think that upsizing the compressor a tad (exactly like what the MK8 turbos seem to have done) could be done to account for this, but it just plain isn't necessary for that kind of application. You COULD run the Venturi on the street and block it off at the track if you really wanted to. A simple ball valve could make it dead easy to do. I have one to play with, but it's kinda on the heavy side and don't think I want it bouncing around.
 

tehfalcon

Passed Driver's Ed
Location
United States
People all concerned about needing to change their TIPs on cars that don't see track.

And PMs (on FB) from people who "I've been running x TIP and never had problems with it"... like yeah. Driving in a straight line isn't as stressful on the PCV as tracking. By a long shot.


Like... I mentioned it multiple times that actual "problems" are almost never going to be experienced on the street. Unless you have actual tangible problems... your setup could be "less than ideal" but don't worry about it. Even the OEM system blips into positive pressure for a split second taking off from stops.

Is it great? No.

Now if you're putting actual pressure on the crankcase during a pull... I suspect bigger turbos/crazy boost MIGHT actually increase in crankcase pressure if the amount of blowby exceeds the additional airflow of the turbo suctioning on the PCV system.

But if it balances out to at least "not positive" in the meat of the pull, it's probably fine "enough" on the street. Hell, @Diggs24 has been on the MK8 basic retrofit for a few months now.

Doing the full retrofit is NOT meant for people who want to extract every single last horsepower from their car on the edge of reliability. Adding WGDC isn't the way to do that. If choosing a new (hybrid) turbo, I DO think that upsizing the compressor a tad (exactly like what the MK8 turbos seem to have done) could be done to account for this, but it just plain isn't necessary for that kind of application. You COULD run the Venturi on the street and block it off at the track if you really wanted to. A simple ball valve could make it dead easy to do. I have one to play with, but it's kinda on the heavy side and don't think I want it bouncing around.
Any idea why the Tiguan uses the Venturi in the first place?
 

hans611

Lost
Location
Miami
Car(s)
'16 Golf R 6MT
Basically the main difference between the Epman or Unitronic TIPs (which hurt vacuum, but not completely throwing it out the window like the BMS did) is that they have a smooth transition into the compressor housing. Whereas the BMS (and the CTS V2 which tested very low peak TIP vacuum levels with a gauge).

I don't think that vacuum level is directly correlated to airflow but moreso the port location and transition into the compressor housing. I PREDICT that the parts with a large dia and then necks down into the compressor (with the PCV on the large diameter portion) are more likely to give less vacuum on the TIP.

I have the 034 TIP... what do you think this bottleneck on the PCV is doing? lol, probably making it even worse....?
It also has a rough transition to the compressor housing like the CTS or BMS....

1708119598564.png
 

Roald

Go Kart Champion
Location
Ohio
Car(s)
GTI mk 7 2017
So I lost track of the catch can thing…
I have a 100% stock intake and I’m still getting clouds on the hard left hand turns.
Should I still be considering a CC?

I don’t have any plans to “track” the car. It’s DD in stop and go city traffic for me and autox during the summer.

I have been getting a decent amount of oil cap seep, and some seeping around the rear valve cover near the cap.
 

GTI_Owner

Go Kart Champion
Location
USA
Car(s)
2016 GTI
But how will the Blaze intake do with it's mongo integrated TIP. This is the real question. 🤣🤣🤣
Unless they have specifically designed the attachment to generate a vacuum it will likely have less vacuum than the traditional port location since it is further upstream.
034-intake-pressure-drop-test.jpg

I have the 034 TIP... what do you think this bottleneck on the PCV is doing? lol, probably making it even worse....?
It also has a rough transition to the compressor housing like the CTS or BMS....

View attachment 299501
It is approximately equivalent to another aftermarket TIP I've measured that is similar in design to the BMS TIP. If you are splitting hairs the 034 measured a slightly greater vacuum at the same airflow rate.
 

yakev724

Go Kart Champion
Location
NYC
Car(s)
2015 S3
Jumped the gun on pcv sensor/harness. My car doesn’t have SAI 🤦‍♂️

If anyone wants it PM me, will let it go for cheap.
 

GTIfan99

Autocross Champion
Location
FL
So I lost track of the catch can thing…
I have a 100% stock intake and I’m still getting clouds on the hard left hand turns.
Should I still be considering a CC?

I don’t have any plans to “track” the car. It’s DD in stop and go city traffic for me and autox during the summer.

I have been getting a decent amount of oil cap seep, and some seeping around the rear valve cover near the cap.
No, you should retro fit a mk8 PCV.
 

DerHase

Autocross Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
So I lost track of the catch can thing…
I have a 100% stock intake and I’m still getting clouds on the hard left hand turns.
Should I still be considering a CC?

I don’t have any plans to “track” the car. It’s DD in stop and go city traffic for me and autox during the summer.

I have been getting a decent amount of oil cap seep, and some seeping around the rear valve cover near the cap.

Tuned it no?

That’s gone over near the beginning of the video. That affects it too.

I’m at VIR currently testing my theory with the “worst” TIP I tested now. Doesn’t guarantee the BMS will smoke, but I’m logging crankcase pressures with both basic and full retrofit. With a rear facing GoPro to check for smoke.

My car hasn’t smoked with the MK8 PCV period in the last 6 months, so we’ll see if the basic retrofit + BMS TIP can make that change.

2 sessions in with full retrofit and it with zero issues running 2:13s on last years brakes and tires.
 

Torrid

Ready to race!
Location
Wisconsin
Car(s)
2018 GTI Autobahn
No, you should retro fit a mk8 PCV.
I'll be keeping an eye on this oil issue. I have the Racingline oil cap and the upgraded red and green seals that are available online. If I see any other oil I think I'll do the MK8 upgrade. I can't say because I hit a deer less than a week after replacing the cap and I did not see any other oil seepage at the time. It's been a month now and I still do not have the car back, but I should have it Monday. I just watched your video from a few days ago as I've been quite interested in what's going on here. As much as I'd be quick to blame the IE Stage 1 tune, I noticed it before I installed the tune and thought it was odd. I only noticed oil from the cap.

As I watched the video that was my main question, which you did mention recommending the MK8 upgrade. If I have any other oil pushing issues obviously the next step should be replacing the PCV and as far as I'm concerned, if I'm going to be in there anyway, I'll just convert to the MK8 setup especially if you do consider this to be a worthwhile upgrade. I'm glad I found this thread and watched your videos because I had originally thought I would have been in need of a catch can, but as much road use as my car sees I now see that would overall cause me more issues.
 

yakev724

Go Kart Champion
Location
NYC
Car(s)
2015 S3
Believe these are the ECU SAI sensor pins, ordered what I need to rig up a harness for my (non-SAI) car to run a PCV pressure sensor in its place/log via simos, hopefully it works off the bat. Will report back.

1708366210977.png
 

DerHase

Autocross Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
I'll be keeping an eye on this oil issue. I have the Racingline oil cap and the upgraded red and green seals that are available online. If I see any other oil I think I'll do the MK8 upgrade. I can't say because I hit a deer less than a week after replacing the cap and I did not see any other oil seepage at the time. It's been a month now and I still do not have the car back, but I should have it Monday. I just watched your video from a few days ago as I've been quite interested in what's going on here. As much as I'd be quick to blame the IE Stage 1 tune, I noticed it before I installed the tune and thought it was odd. I only noticed oil from the cap.

As I watched the video that was my main question, which you did mention recommending the MK8 upgrade. If I have any other oil pushing issues obviously the next step should be replacing the PCV and as far as I'm concerned, if I'm going to be in there anyway, I'll just convert to the MK8 setup especially if you do consider this to be a worthwhile upgrade. I'm glad I found this thread and watched your videos because I had originally thought I would have been in need of a catch can, but as much road use as my car sees I now see that would overall cause me more issues.

As far as I can tell the oil cap is designed to vent in the case of excess crankcase pressure. Even an OEM bone stock car will have small periods of positive pressure on the crankcase. Mostly in taking off from a stop. If you do it at a "normal" pace - you're usually hovering right around 0psi manifold pressure. There's no vacuum from the TIP yet, but the intake blue path vacuum source is also gone. The stock car is "meant" to tolerate it to some extent. It just so happens that basically everything we do to it makes it worse.


The Venturi still has this same specific weakness, but the difference is as soon as you're in any kind of boost, it is able to draw the crankcase down. I don't think it's a big deal for the diaphragm to be open under very low load type situations, but in theory if one were pussyfooting it in a VERY long sweeper it might be possible to induce problems. I tried driving the car with that in mind in basic retrofit form to see what goes on with crankcase/PCV pressures in basic retrofit form.

Here's a little preview of what I'll be looking over for the next week or so...

I ran it for 2 sessions Saturday morning in full retrofit form. Zero problems. Zero oil consumption. With the BMS TIP.

Then ran it with the BMS TIP in basic retrofit form for 2 sessions... I didn't get it to smoke profusely like I was somewhat expecting. There wasn't any notable KR - the highest knock avg I recorded all weekend was -1.125... but looking at the crankcase sensor:

1708391784170.png




When checking the oil after those sessions... it was dribbling oil from the cap venting.

1708392106505.png



And for comparisons sake out of the same corner (T17/Hog Pen leading onto the front straight)... here's what's going on with the Venturi fitted:

1708392220991.png
 
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