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

[nomunic]

Collecting the info?
I'm reaching out to anyone I see having issues or running a full retrofit successfully to try and find trends. I try to keep it updated as much as possible. I've put a few of the problems w/ basic retrofit on there mainly to run VINs for part numbers.

If you mean the 15-16 cars running full retrofit without issues, the PCV modification mentioned here has helped. 1 on track and 2 on the street so far.

Trip report regarding the PCV modification experiment:
https://www.datadrivenmqb.com/tripreports/2024tsccax6



If I recall correctly, you did the retrofit but got some smoking right? Basic or full? I have you down as basic on that page. You may need to burn a hole in the bottom of the PCV to do the same as well.

I've ordered another valve myself so I can get a video modifying it/how not to fuck it up.

I get some smoking on pulls with the mk8 PCV full retrofit on my 17 gti. Smoke on startup typically as well but I believe it’s the valve seals.

 

[DerHase]

I get some smoking on pulls with the mk8 PCV full retrofit on my 17 gti. Smoke on startup typically as well but I believe it’s the valve seals.

PM me your VIN and I'll run it some time tomorrow. Is it a small puff barely visible... or a big plume of smoke like this?

If valve seals are leaking then there's potential that it's pulling more air through the blow-by passage and taking oil with it.

Modifying the valve might hide potentially mask the symptoms on pulls, but I doubt would do anything for smoking on startup.

 

[nomunic]

PM me your VIN and I'll run it some time tomorrow. Is it a small puff barely visible... or a big plume of smoke like this?

View attachment 308419

If valve seals are leaking then there's potential that it's pulling more air through the blow-by passage and taking oil with it.

Modifying the valve might hide potentially mask the symptoms on pulls, but I doubt would do anything for smoking on startup.

Comes out as a puff and then sticks around for a few seconds, definitely not like that lol. 3vw547au5hm012655

 

[DerHase]

So just found out this guy has been making over 700whp on the MK8 full retrofit since March doing 1-2 pulls per day with no problems...

It's a 2017 GTI in the OS group w/ built engine running 43psi on a PTE 6266 v-band 0.83 A/R, ported head etc.

He recently bumped the pressure up to 47psi and has started getting a bit of smoke on long pulls. We're thinking that this is about the limit (for straight line drag use) of an unmodified MK8 valve (in a 17+ engine block), and he's now moving so much blow-by through the block passage that it's taking oil with it.

Similar symptom as these cars smoking on track, but due to different reasons. The smoke he said is subtle (not a massive plume) which leads me to believe he's just overwhelming the block passage.

He's ventilated the the valve to the cam cover just like Jacob's car to see if it sorts his issues out. At this power level I think he's expecting to see 750+ which is bonkers.

*I will say that I think this is a pretty high risk test of the valve and not sure how long I'd expect it to live. I'd probably treat it as a 1-2x per year maintenance item personally. I'm curious to know at what point the plastic case breaks trying to hold back nearly 50psi with lots of heat and cool cycles making it brittle over time. There's the potential for the small check valve (which keeps boost from entering the rest of the valve) to fail and put a large amount of pressure on the crankcase, though I think it would result in a huge power loss (boost leak) as well. Due to the way the valve is laid out, I can't imagine it will put 100% full boost pressure to the crankcase, but it would result in countering the vacuum source and regardless wouldn't be good at those pressure levels.

He's been unable to get anything else to work, including an APR plate which was putting pressure on the crankcase at idle to the point that his turbo was not draining oil, forcing it out at the turbine seal into the downpipe. I personally think something was very wrong with his kit, maybe a collapsed hose or something weird. I would not expect this to be possible at idle, even with a relatively loose built engine. He commented that the MK8 full retrofit has been problem free and functioning like OEM up until he bumped the boost up more.

I've spoken with a few people with 2015 or 16 MY built engines (taking the rings, rear main seal, etc. out of the picture), and they continue to have PCV problems with the MK7 BL or MK8 valves, so I'm actually wondering if there might be a physical difference in the engine blocks in 15-16 vs 17+ that make them more likely to have issues. A narrower block passage, a worse/differently designed coarse AOS, etc. are some possibilities that come to mind.

 

[SaucyMuffin]

Just wanted to follow up with my earlier post. Did an initial oil separator and N80 valve. Didn’t do anything. Did a piston soak with Berryman’s B12. No more smoke. So, for me, that was the issue. Mind feels a little better now since I didn’t want to start diving down a rabbit hole and spend to not find a solution.

 

[tmw2442]

Just wanted to follow up with my earlier post. Did an initial oil separator and N80 valve. Didn’t do anything. Did a piston soak with Berryman’s B12. No more smoke. So, for me, that was the issue. Mind feels a little better now since I didn’t want to start diving down a rabbit hole and spend to not find a solution.

Assuming you changed the oil afterwards; glad it worked but...please, tell us you did an oil change within a drive or two at the absolute most, after the b12 soak. Maybe even a change, then a couple days of driving and other change to flush everything.

 

[SaucyMuffin]

Umm yeah, of course the oil was changed after a couple miles to test. After 500 I installed another new oil filter as well. Should do the trick for a while. However I have been reading about HPL’s Engine Clean and following up with their oil since my weekly mileage of driving has dropped tremendously. I’d say if anyone noticed some slight puffing at start, try it, very easy to do and lots of positive information and results on various auto brands.

 

[bbroecker37]

I just completed the MK8 PCV retrofit on my 2016 GTI. I haven't done the full retrofit yet. I'm still on the stock IS20 turbo but plan to upgrade to the GT2260S soon. So the 034 turbo muffler with the test ports won't work with the new turbo. Do you guys think the stock plastic charge pipe is thick enough to drill and tap for the venturi?

 

[nomunic]

I just completed the MK8 PCV retrofit on my 2016 GTI. I haven't done the full retrofit yet. I'm still on the stock IS20 turbo but plan to upgrade to the GT2260S soon. So the 034 turbo muffler with the test ports won't work with the new turbo. Do you guys think the stock plastic charge pipe is thick enough to drill and tap for the venturi?

I’m facing this issue rn, probably better off buying a charge pipe kit with a port. No matter what I do I can’t get the barb to stay in even with jb weld

 

[fretburnr]

Stock turbo inlet pipe also?

Could probably get away with replacing with an updated stock one (AP revision). I do suspect that the BM from a Golf R would be the equivalent of the MK7 "upgrade" for a GTI like the BL craze but for the cars w/ the PCVs that breathe on the cam cover (15-18 CXCA/CXCB).

https://www.datadrivenmqb.com/drivetrain/just-the-tip-testing

Watch from the 22:36 time stamp to visualize what's going on:

While that's focused on turbo inlet pipes.. you can see the wild difference between any of the full retrofit vs the basic retrofit even on stock TIP:

View attachment 308139

The bottom graph is the important one. Any time that the crankcase vacuum isn't leveled off around -0.7 to -0.9ish psi... the diaphragm is open meaning volume of air that will potentially move oil along with it.

While there haven't been any issues with 2017s yet (all retrofits were successful AFAIK), I'd either do the full retrofit or just keep a stock MK7 style valve. If you're not doing the full retrofit then it's basically just a lateral move IMO.

If you stick with MK7 valves, the AP is likely best, though I suspect the BM will work as good or better just based on being the same design type and meant for a higher performance application (like BL vs BK for 2019+ GTIs).



Maybe, maybe not. I mean stuff can also just fail. If cleaning it off and it comes right back in a short amount of time or you have any other seal issues then I'd look into it a bit more.



IMO: If you're tracking the car then you really want to make sure the diaphragm stays closed as much as possible. That means you either run an OEM TIP + the appropriate MK7 PCV or MK8 basic retrofit and hope there are no issues or run the full retrofit with the following caveats:

2015-16 GTI or 1.8T: I'd hold off on the retrofit until further notice

2017-18 GTI or 1.8T: Very likely good to do the retrofit, but I would either do the full retrofit from the beginning or do an AP valve (plus BMS catch can if you really want - everything else on the market is trash)

2019+ GTI or 1.8T: MK8 retrofit basic is probably a lateral move vs just replacing with another MK7 valve, but gives you the flexibility to do the full retrofit in the future.

2015-17 R: Not a ton of data just yet to know one way or the other. I don't think I'd bother with a basic retrofit at all, go straight to full retrofit or get a new BM valve.

2018 R: Bit of a question mark but should be good to do whatever. Uses the same pistons/rings as the 2019 does, but uses the cam cover venting PCV stock. Again if you have no intention of doing the full retrofit I'd just do a replacement BM valve.

2019 R: Should be good to go on basic or full retrofit. Most up to date valve per VW is the BL for reference.

The reasoning behind wanting the full retrofit if feasible is pretty well shown here. Running a stock TIP will be better than the BMS one used, but it will still be far less optimal than the full retrofit (again, assuming it's not a 2015-16 GTI or 1.8T... with varying levels of "risk" pending other models/years).

Thank you very much. This is extremely helpful. I've watched the videos and the live CC pressure data on track tells the whole story IMO.

At this time, I'm on 100% stock hardware, so stock TIP, no TMD, etc. I don't plan to change any hardware unless I have to, in order to stay SCCA street-class legal. I wasn't planning on a TMD but if it's needed for reliability I'll make the concession.

Is the difference between Basic and Full retrofit just the TMD with NPT fittings? Just clarifying; it looks like we need to add that vacuum source pre-turbo to use the venturi that would otherwise be unused in the basic retrofit? I'm basing this on your parts list here https://www.datadrivenmqb.com/mk8pcv and info here https://www.datadrivenmqb.com/drivetrain/pcvtechtalk

Also, I presume for the full retrofit, we'll need some 5/16 vacuum hose to plumb to the venturi (in place of the cap that's used in the basic retrofit)?

 

[nomunic]

Thank you very much. This is extremely helpful. I've watched the videos and the live CC pressure data on track tells the whole story IMO.

At this time, I'm on 100% stock hardware, so stock TIP, no TMD, etc. I don't plan to change any hardware unless I have to, in order to stay SCCA street-class legal. I wasn't planning on a TMD but if it's needed for reliability I'll make the concession.

Is the difference between Basic and Full retrofit just the TMD with NPT fittings? Just clarifying; it looks like we need to add that vacuum source pre-turbo to use the venturi that would otherwise be unused in the basic retrofit? I'm basing this on your parts list here https://www.datadrivenmqb.com/mk8pcv and info here https://www.datadrivenmqb.com/drivetrain/pcvtechtalk

Also, I presume for the full retrofit, we'll need some 5/16 vacuum hose to plumb to the venturi (in place of the cap that's used in the basic retrofit)?

Not sure about the rules for the SCCA but if you’ll want the full retrofit (which is reportedly an upgrade over stock) then you’ll need that vacuum source. Best way to get that is through a tmd with the barb attached. Otherwise you’ll be trying total stock charge pipes which is annoying

 

[Ambitorus]

Found out during an HPDE that I'm getting quite a bit of oil coming out of the PCV assembly itself. This recess next on the left side of the PCV pretty much filled up with oil over the course of a session and you can see where it's getting blown up over the coil packs as well.

Is this also a known issue with the Mk7 PCVs? This is a 2018, have not verified exactly which version of the PCV this is. I'm planning on doing the full retrofit anyway, so I'm not overly worried, but was curious if this is a symptom of the same problem. Aftermarket inlet & TIP so yes I am aware the root cause of the issue is me.

Also, for the full retrofit, is the 034 TMD really necessary or can I just tap into boost on the stock outlet coupler with one of these?

 

[bbroecker37]

Found out during an HPDE that I'm getting quite a bit of oil coming out of the PCV assembly itself. This recess next on the left side of the PCV pretty much filled up with oil over the course of a session and you can see where it's getting blown up over the coil packs as well.View attachment 309242

Is this also a known issue with the Mk7 PCVs? This is a 2018, have not verified exactly which version of the PCV this is. I'm planning on doing the full retrofit anyway, so I'm not overly worried, but was curious if this is a symptom of the same problem. Aftermarket inlet & TIP so yes I am aware the root cause of the issue is me.

Also, for the full retrofit, is the 034 TMD really necessary or can I just tap into boost on the stock outlet coupler with one of these?

I noticed I had a leak around where the hose connects to the PCV. I also had a little bit of oil on one of my spark plugs.

I’m also wondering if the stock coupler is big enough to install one of those bungs.

 

[DerHase]

I just completed the MK8 PCV retrofit on my 2016 GTI. I haven't done the full retrofit yet. I'm still on the stock IS20 turbo but plan to upgrade to the GT2260S soon. So the 034 turbo muffler with the test ports won't work with the new turbo. Do you guys think the stock plastic charge pipe is thick enough to drill and tap for the venturi?

I wouldn't bother. Would want to just get some charge pipes that have a 1/8npt bung on them already for ease of install. You'll want to run a 1/8npt to 1/4in barb fitting, run 1/4in rubber hose to a 1/4 barb to 3/8 barb adapter, to 3/8 hose at the Venturi itself. Clamps/zip ties/etc on all connections because you don't want it blowing off under boost.

I’m facing this issue rn, probably better off buying a charge pipe kit with a port. No matter what I do I can’t get the barb to stay in even with jb weld

This is the main problem. While *I* have a PCV sensor... if a fitting were to leak you'd probably never know it and you risk overspinning the turbo... which is a big problem on the 2260 in particular.

Thank you very much. This is extremely helpful. I've watched the videos and the live CC pressure data on track tells the whole story IMO.

At this time, I'm on 100% stock hardware, so stock TIP, no TMD, etc. I don't plan to change any hardware unless I have to, in order to stay SCCA street-class legal. I wasn't planning on a TMD but if it's needed for reliability I'll make the concession.

Is the difference between Basic and Full retrofit just the TMD with NPT fittings? Just clarifying; it looks like we need to add that vacuum source pre-turbo to use the venturi that would otherwise be unused in the basic retrofit? I'm basing this on your parts list here https://www.datadrivenmqb.com/mk8pcv and info here https://www.datadrivenmqb.com/drivetrain/pcvtechtalk

Also, I presume for the full retrofit, we'll need some 5/16 vacuum hose to plumb to the venturi (in place of the cap that's used in the basic retrofit)?

TECHNICALLY the MK8 full retrofit is not "legal" for SCCA street class. Call a dealer (NOT some online parts look up!) and verify by VIN which is the latest revision.

It is PROBABLY:
AP for all 15-18 GTI and all 15-21 1.8L
BM for all 15-18 Golf R
BK for all 19+ GTI
BL for 19 Golf R

If you keep the stock TIP, the stock system while not "great" should work. I SUSPECT on the BK AND BL ONLY valves you could ventilate those MK7 valves to the cam cover to help keep oil from being pulled up the block passage like I've been doing on the MK8 valve. If you ever replace the TIP, then this setup will still not be doing you any favors for crankcase pressure, but it should still be more resistant to pushing oil up the passage. This modification should NOT be done to the AP/BM valves because they already only breathe on the cam cover. I THINK the problem with those valves is they have no way to drain any oil mist that DOES make it inside, and so they build up crap inside over time.

That said, I don't think anybody will give you shit for running a MK8 basic retrofit. This is what the SCCA solo national champ used last year for STH where it's also technically not legal (though catch cans are as long as the stock PCV isn't replaced.

SCCA rules are dumb and I will die on that hill

Found out during an HPDE that I'm getting quite a bit of oil coming out of the PCV assembly itself. This recess next on the left side of the PCV pretty much filled up with oil over the course of a session and you can see where it's getting blown up over the coil packs as well.

Is this also a known issue with the Mk7 PCVs? This is a 2018, have not verified exactly which version of the PCV this is. I'm planning on doing the full retrofit anyway, so I'm not overly worried, but was curious if this is a symptom of the same problem. Aftermarket inlet & TIP so yes I am aware the root cause of the issue is me.

Also, for the full retrofit, is the 034 TMD really necessary or can I just tap into boost on the stock outlet coupler with one of these?

Someone else has had problems trying to use that fitting I think. If you have an 18 R it should be a BM, otherwise if GTI/1.8 it should be an AP valve.

I would strongly recommend the 034 TMD only because it greatly simplifies things and it allows you to use the OEM Tiguan hose without any issues.

For track use I think I'm recommending people ventilate the valve from the get go, though obviously that's kind of irreversible. Throwing it on and seeing what happens is probably the best bet initially, can always cut later if issues are encountered. I'm currently putting stuff together to publish info on that, personal life stuff with my parents has kind of taken priority for the time being though.

PCV failure is generally just ingesting oil and some light leaks (maybe) - your leak looks like it could be much worse, like cam cover, etc. I'd clean it off REALLY good to figure out exactly where it's coming from.

I noticed I had a leak around where the hose connects to the PCV. I also had a little bit of oil on one of my spark plugs.

I’m also wondering if the stock coupler is big enough to install one of those bungs.

Again this sounds more like a cam cover seal issue. Could be from small bits of pressure on the crankcase many times over the course of time, or just time to reseal.

Just go straight for the 034 TMD. Unless you have a big turbo that can't accept a TMD like that, there's really no reason to waste time trying other stuff IMO. It allows the Tiguan hose to be used without any fuss.

 

[Ambitorus]

For track use I think I'm recommending people ventilate the valve from the get go. I'm currently putting stuff together to publish info on that, personal life stuff with my parents has kind of taken priority for the time being though.

"Ventilate the valve from the get go" as in do the full retrofit only and don't bother with the basic, yeah?