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

DerHase

Autocross Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
Alright yeah so because I'd rather install parts than remove them/go back to stock... someone make a shopping list/kit and some idiot-proof instructions for those of us who are a little slow, then shut up and take my money

How to/Basic retrofit w/ part numbers in the video description:


Full retrofit specifics... not really a "how to" but covers the basics/issues encountered when done to an otherwise stock car. Obviously may run into other/different challenges with non-OE charge pipes etc.


Parts list for full retrofit:


You can also use one of the hose clamps that comes with the 90 deg fitting with on the N80 hose to PCV as well... since the barb on the MK8 unit is just marginally larger than the MK7 valve barb.

Also you'll want to use some teflon tape or thread lock on the NPT fittings to seal them.
 
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DerHase

Autocross Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
Also accidentally ordered a BMS catch can. Should be here next week, but will likely not start playing with until after VIR the following weekend.

I'm wanting to put numbers/logs to as much stuff as I can to prove (or disprove) the theories discussed thus far.

BMS due to:
- Plugs into OEM TIP hose... which means the Tiguan hose will also plug right into it.
- In basic retrofit form I can just buy some big ass long hoses to play around with showing how added VOLUME (hose length, which would also translate to can size) affects crankcase pressures. And why with any OEM PCVs... a catch can is bad in general without the Venturi.
- Due to the Venturi being pre-catch-can, it means there will be no delay of vacuum getting to the PCV like there is with any MK7 valve or MK8 basic retrofit... with the added flexibility of MAYBE using longer hoses between the can and TIP to purposely dull the vacuum draw from the TIP, relying more heavily on the Venturi only (which based on the BMS w/ Venturi being far more stable than OEM TIP w/ Venturi... is probably a safe bet).
- Because this removes the primary PROBLEM with a catch can, it means there is really no downside to running one with the Venturi.

Basically the MK8 valve w/ Venturi opens up a LOT of tuning options to dial in PCV vacuum pressure. This is a GOOD thing because it then becomes an adjustable solution regardless of turbo/TIP combo.

Going strictly off of the PCV vacuum source logged on all the TIP/Venturi combinations... I'm going to go out on a limb and say that ideally... we're going to be shooting for -2 to -3.5psi peak at the PCV sensor to keep the crankcase pressure stable but also maintain enough to keep the level under control in transitions.
 

Klrider44

Go Kart Champion
Location
Bucks county PA
Legend - my harness is on its way and just finished fabbing up the venturi to my charge pipe hose. Curious to measure the impact.

In case anyone needs this setup (though keep in mind not many aftermarket charge pipes have a larger silicone hose like EQT): bung fitting 1 fitting 2 hose

View attachment 297564

View attachment 297565
Any pics of how this is routed when installed? This is a viable option instead of the 034 TMD correct? I would rather do this since I already have the EQT charge pipe.
 

Torrid

Ready to race!
Location
Wisconsin
Car(s)
2018 GTI Autobahn

DerHase

Autocross Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
@DerHase Aftermarket PCV replacement? Am I missing something here or are you familiar with this one? It's certainly pricey, but are there any benefits here? I do have concerns with the catch can setup. I stumbled across thing thing from a Humble Mechanic video.

https://www.racingline.com/oil-management-catch-can-mqb-golfr-golfgti-audis3-leoncupra

If the car is a dedicated track-only car... It's probably a good compromise.

Like every other plate system it does away with the vacuum port at idle/low load so every time you stomp on the gas, you're going to have positive crankcase pressure for a few seconds at least. I'm working on getting an APR plate on my car in the next month or so for testing purposes to add to the data.

How well any plate system performs will be relative to how much vacuum the TIP pulls at any given time. Too much and it'll fill a catch can ridiculously fast. Too little and it'll basically allow pressure on the crankcase and you still have the dumb maintenance of constantly emptying it in cooler weather. Excessive crankcase pressure can also potentially fill it up too.

The best part is because it has no diaphragm or regulator, it cannot ever be "ideal" under all driving circumstances.

It's a legit racecar part and works well enough in that application: where you're WOT more than 50% of the time and you're more likely to blow the engine up than ever see 100k miles.
 

Torrid

Ready to race!
Location
Wisconsin
Car(s)
2018 GTI Autobahn
If the car is a dedicated track-only car... It's probably a good compromise.

Like every other plate system it does away with the vacuum port at idle/low load so every time you stomp on the gas, you're going to have positive crankcase pressure for a few seconds at least. I'm working on getting an APR plate on my car in the next month or so for testing purposes to add to the data.

How well any plate system performs will be relative to how much vacuum the TIP pulls at any given time. Too much and it'll fill a catch can ridiculously fast. Too little and it'll basically allow pressure on the crankcase and you still have the dumb maintenance of constantly emptying it in cooler weather. Excessive crankcase pressure can also potentially fill it up too.

The best part is because it has no diaphragm or regulator, it cannot ever be "ideal" under all driving circumstances.

It's a legit racecar part and works well enough in that application: where you're WOT more than 50% of the time and you're more likely to blow the engine up than ever see 100k miles.
That was the biggest thing I was wondering. How it is when it isn't pushed. I greatly appreciate your time to respond. I think where I have arrived is just preemptively replacing the stock PCV with a new one. I have 55k miles and it may just be cheap insurance. I'm horrible about over thinking these things anyway and running elevated boost levels may have side effects I didn't think of, but I try and do what's best for my engine while at the same time modifying.
 

DerHase

Autocross Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
That was the biggest thing I was wondering. How it is when it isn't pushed. I greatly appreciate your time to respond. I think where I have arrived is just preemptively replacing the stock PCV with a new one. I have 55k miles and it may just be cheap insurance. I'm horrible about over thinking these things anyway and running elevated boost levels may have side effects I didn't think of, but I try and do what's best for my engine while at the same time modifying.

I can say without a doubt that ridiculous high flow TIPs are 100% ruining the OE PCV ability to function.

OEM, APR (or at least my $46 Epman Amazon TIP), or Unitronic seem to be “not that bad” while still offering increase in flow.

BMS hands down is fucking terrible and will never allow the diaphragm to close (under load). Only at idle/out of boost.
 

Torrid

Ready to race!
Location
Wisconsin
Car(s)
2018 GTI Autobahn
I can say without a doubt that ridiculous high flow TIPs are 100% ruining the OE PCV ability to function.

OEM, APR (or at least my $46 Epman Amazon TIP), or Unitronic seem to be “not that bad” while still offering increase in flow.

BMS hands down is fucking terrible and will never allow the diaphragm to close (under load). Only at idle/out of boost.
Yeah, I don't think the piggyback ones that retain the stock PCV is the answer. I've seen based on your data that the valve can't cope with the extra airspace. I wonder about the plate style PCV deletes. I was looking at the Racingline setup because I love their attention to detail on construction, but I'm not 100% convinced this old school straight PCV setup is right for a turbocharged vehicle that isn't track only. The GTI is my first turbo car so this PCV design is completely new to me. I'm used to a crankcase vent going straight to the intake tube with LS V8s which is my background and for obvious reasons that's not what we have here. It's not a surprise that VW has done many revisions as they've honed this approach. Obviously they're going into this to be the most reliable setup for the car they sell. I just wonder how this is affected by tuned cars and wonder if I would benefit from another solution. What adds to my scenario is that I see a lot of highway miles, but I also push the car hard when I can. I'm not sure at this point that either setup is ideal for how I drive the car. I've done a lot of reading into your data and I'm really pleased to see that you'll be testing the APR plate. It's not that I think any aftermarket company has the perfect solution for my use case, but I also wonder how much of VW's solution is shaped and hindered by emissions restraints. Going aftermarket in general skews these results and adds other variables beyond the standard emissions requirements.

I was getting some smoke and smell from under hood when it got cold which got worse after my deer strike. According to the body shop that is fixing my car they found the washer fluid reservoir to be cracked and leaking onto the radiator. I'm thinking this was cracked before the accident and with it being winter washer fluid it had a fairly high smoke/gas point. There was an odd smell under hood I could not place that wasn't oil or coolant. It almost smelled like rubber. It got much worse after the accident. There's obviously a lot of variables in a street car, but all of this has now been replaced and I'll have the car back at the end of the week. I've not had any increase in oil consumption compared to before the IE Stage 1 tune so it may be all for nothing anyway.

I look forward to your test results of the APR plate and I'll stand by for the time being overthinking my next mod like I always do. 🤣
 

yakev724

Go Kart Champion
Location
NYC
Car(s)
2015 S3
How is this holding up? Was thinking about going this route since I have the EQT pipe and don’t have a Venturi yet. Just the MK8 valve and Tiguan hose

Any pics of how this is routed when installed? This is a viable option instead of the 034 TMD correct? I would rather do this since I already have the EQT charge pipe.

Unfort. haven't been able to test thoroughly/log yet but have done a few pulls and it seems to be solidly in place and not leaking. You want the hose to be about as long as an iphone and barb angled a bit towards the firewall. Don't drill the hole in the charge hose too far from the edge, as it'll be tricky to get a wrench on it to tighten (though I needed to use an adjustable so maybe just a me problem).

Will try to take some logs this week, only time there isn't traffic here is at 5 am :)

IMG_0367.jpegIMG_0369.jpegIMG_0370.jpeg
 

DerHase

Autocross Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
Yeah, I don't think the piggyback ones that retain the stock PCV is the answer. I've seen based on your data that the valve can't cope with the extra airspace. I wonder about the plate style PCV deletes. I was looking at the Racingline setup because I love their attention to detail on construction, but I'm not 100% convinced this old school straight PCV setup is right for a turbocharged vehicle that isn't track only. The GTI is my first turbo car so this PCV design is completely new to me. I'm used to a crankcase vent going straight to the intake tube with LS V8s which is my background and for obvious reasons that's not what we have here. It's not a surprise that VW has done many revisions as they've honed this approach. Obviously they're going into this to be the most reliable setup for the car they sell. I just wonder how this is affected by tuned cars and wonder if I would benefit from another solution. What adds to my scenario is that I see a lot of highway miles, but I also push the car hard when I can. I'm not sure at this point that either setup is ideal for how I drive the car. I've done a lot of reading into your data and I'm really pleased to see that you'll be testing the APR plate. It's not that I think any aftermarket company has the perfect solution for my use case, but I also wonder how much of VW's solution is shaped and hindered by emissions restraints. Going aftermarket in general skews these results and adds other variables beyond the standard emissions requirements.

I was getting some smoke and smell from under hood when it got cold which got worse after my deer strike. According to the body shop that is fixing my car they found the washer fluid reservoir to be cracked and leaking onto the radiator. I'm thinking this was cracked before the accident and with it being winter washer fluid it had a fairly high smoke/gas point. There was an odd smell under hood I could not place that wasn't oil or coolant. It almost smelled like rubber. It got much worse after the accident. There's obviously a lot of variables in a street car, but all of this has now been replaced and I'll have the car back at the end of the week. I've not had any increase in oil consumption compared to before the IE Stage 1 tune so it may be all for nothing anyway.

I look forward to your test results of the APR plate and I'll stand by for the time being overthinking my next mod like I always do. 🤣

Bottom line if you’re not tracking the car at all then any kind of plate is a dumb solution as you’ll then be putting (light) pressure on the crankcase at all times you’re out of boost. There are multiple people running the MK8 basic retrofit pushing 450-550whp with no problems on the street. I suspect they’ll need the Venturi for track use though like @yakev724 .

I beat the shit out of my car on track for 20 min at a time and have had zero issues in basic or full retrofit configuration (with stock TIP). If you’re not seeing 260F+ oil temps you’re not really stressing the car that much (and assuming you’re not testing the strength of the stock bottom end parts - not really stressing in the same way).

There’s really nothing else to it. There are countless people who have issues with any of the plate systems. Knowing what I know now, it’s likely correlated to the TIP they’re running not being a good match for whatever other clusterfuck of a setup they have. The TIP vacuum testing will possibly be even more relevant for people with plates because there is no regulator to dial down the vacuum.

What’s a lot harder to capture is the fact that the BMS TIP is putting 0.20psi on the crankcase for about 10 seconds every time you’re taking off from a stop. Any plate system will be worse because at least the OEM PCV gets to start out at -0.8 to -0.9psi. Plates will all be positive at idle with no volume of vacuum storage to help.

If/when it’s released, I’d only really consider the Radium plate. They actually do real R&D, not just copy the looks of TCR stuff and sublet to the lowest bidder on AliExpress.

(This isn’t meant to be taken personally- but it’s frustrating knowing that some degree-less idiot former mechanic has done more R&D for the PCV system on this platform than any of the aftermarket parts companies. The PCV thing is just part of it. Don’t get me started on oil coolers, bump-steer, or CSF radiators 😅

Like really - HOW does any aftermarket company not see the hump inside the OEM TIP and not think “Gee, maybe that’s there for a reason?”)


/rant
 
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Klrider44

Go Kart Champion
Location
Bucks county PA
Unfort. haven't been able to test thoroughly/log yet but have done a few pulls and it seems to be solidly in place and not leaking. You want the hose to be about as long as an iphone and barb angled a bit towards the firewall. Don't drill the hole in the charge hose too far from the edge, as it'll be tricky to get a wrench on it to tighten (though I needed to use an adjustable so maybe just a me problem).

Will try to take some logs this week, only time there isn't traffic here is at 5 am :)

View attachment 299271View attachment 299272View attachment 299273
Very nice, thank you for the info. I’ll be going this route.
 

Nineeightyone

Autocross Champion
Location
Pennsylvania
Car(s)
Scooty Puff Jr
Bottom line if you’re not tracking the car at all then any kind of plate is a dumb solution as you’ll then be putting (light) pressure on the crankcase at all times you’re out of boost. There are multiple people running the MK8 basic retrofit pushing 450-550whp with no problems on the street. I suspect they’ll need the Venturi for track use though like @yakev724 .

I beat the shit out of my car on track for 20 min at a time and have had zero issues in basic or full retrofit configuration (with stock TIP). If you’re not seeing 260F+ oil temps you’re not really stressing the car that much (and assuming you’re not testing the strength of the stock bottom end parts - not really stressing in the same way).

There’s really nothing else to it. There are countless people who have issues with any of the plate systems. Knowing what I know now, it’s likely correlated to the TIP they’re running not being a good match for whatever other clusterfuck of a setup they have. The TIP vacuum testing will possibly be even more relevant for people with plates because there is no regulator to dial down the vacuum.

What’s a lot harder to capture is the fact that the BMS TIP is putting 0.20psi on the crankcase for about 10 seconds every time you’re taking off from a stop. Any plate system will be worse because at least the OEM PCV gets to start out at -0.8 to -0.9psi. Plates will all be positive at idle with no volume of vacuum storage to help.

If/when it’s released, I’d only really consider the Radium plate. They actually do real R&D, not just copy the looks of TCR stuff and sublet to the lowest bidder on AliExpress.

(This isn’t meant to be taken personally- but it’s frustrating knowing that some degree-less idiot former mechanic has done more R&D for the PCV system on this platform than any of the aftermarket parts companies. The PCV thing is just part of it. Don’t get me started on oil coolers, bump-steer, or CSF radiators 😅

Like really - HOW does any aftermarket company not see the hump inside the OEM TIP and not think “Gee, maybe that’s there for a reason?”)


/rant
Sounds like a solid reason to swap back to the factory TIP for the time being.

Can't wait for the bump-steer thread -- let's get some of that knowledge out there, because we've come so far from 'lower == better'
 

tigeo

Autocross Champion
Sounds like a solid reason to swap back to the factory TIP for the time being.

Can't wait for the bump-steer thread -- let's get some of that knowledge out there, because we've come so far from 'lower == better'
Finger width gap measurements bro.
 

Nineeightyone

Autocross Champion
Location
Pennsylvania
Car(s)
Scooty Puff Jr
Finger width gap measurements bro.
Autocross is what brought me to raise my coilovers when I had my JSW, and I purely went with the 'eyeball the control arm angle' approach and even then handling was significantly improved. I can't imagine how much better it would've been had I actually known what I was doing.
 
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