PCV bypass for VW 2.0 FSI Description/DIY (long)

[zoomzoom]

saaber1,
Nice work and great write-up!!
Thanks for sharing.

I do have a question/concern why is use of check valve necessary?

how much back pressure does you cat back exhaust has at WOT?

you will get most blow by at WOT and if that is the time that check valve has to prevent exhaust(due to the back pressure from your cat back) from going into crankcase then you are not getting all the functionality you wanted. Your crankcase will be somewhat pressurized until it overcomes the back pressure of the exhaust...

I guess a good way to test this is to remove check valve and run the hose from exhaust to the cabin and see if you get any exhaust gas out of it during the WOT run?

btw where did you get those freeze plugs?

 

[CBR.worm]

This is an interesting solution to a problem that seems to have been following audi/vw for a long time. My wife has an '04 A4 w/ 1.8t that has had multiple PCV system related failures resulting in all sorts of nastiness from blowing oil seals and popping the dipstick out to excessive sludge. Apparently once the check valve fail the crankcase is subject to turbo boost pressure. Her car now has 55K, and had stuck check valves before 40K and dissolved plumbing by 50K. Doing the work myself I have spent almost $1,000 replacing OE PCV components with new OE PCV components since the warranty expired 2 years ago. Her car has had M1 oil changes every 5K, every other one at the dealership to maintain the 80K sludge warranty. Her ride to work is 14 miles each way at 80mph each day with no traffic and only a couple stops - seems like an ideal life.

I have considered plugging everything and sticking a K&N crankcase breather on the back of the valve cover, but it seems they need some actual fresh air flow to carry out the particulates in the vapor. Maybe a K&N on the front of the valve cover and your line into the exhaust off the back.

We used to do this on bikes, but there were conditions that the crankcase would get pressurized (top end runs typically) and then when you let off the gas all the oil vapor (and some liquid) would dump into the exhaust at once leaving a huge oil cloud behind you. It's amazing how much smoke a teaspoon of oil into the exhaust will make, but I digress.

 

[Turbo_777]

This is an interesting solution. My only concern is that you block out the pipe venting to the turbo intake (behind the motor). This would prevent the venting of PCV gasses under boost since the PCV valve unit channels it that way when under load and under no load it opens and channels the gasses through the intake manifold route. Anyone who wants to see how this works can PM me and I will mail them the VW diagram of how this works.

If you channeled the pipe behind the motor into the exhaust as well, this might work better. I am just not sure what happens to the pressure in the motor as VW designed it to be negitive and when not under load the intake manifold has vacume in it and when boosting the turbo intake pipe (which it the rear one you blocked) is also under vacume.

Just my 2 cents

 

[saaber1]

Originally Posted By: Turbo_777
This is an interesting solution. My only concern is that you block out the pipe venting to the turbo intake (behind the motor). This would prevent the venting of PCV gasses under boost since the PCV valve unit channels it that way when under load and under no load it opens and channels the gasses through the intake manifold route.


That is incorrect. In stock mode the boost from the intake causes the crankcase gasses to be sent to the turbo while car is under boost. When vacuum is present it sends the gases to the intake. In this bypass setup there is no boost acting on the pcv valve it is always under vaccum. I assume you are referring to this diagram:

 

[Turbo_777]

Hi Saaber1,

That is the diagram I was refering to, thanks. I think we are actually saying similar things, just one corretion on what you said.The PCV unit has two valves in it, when there is boost (read pressure in the intake manifold) the PCV acts like a one way valve and stops any flow into the crank case and it routes the flow from the primary oil separator through to the turbo intake (back of the valve cover). Hence I feel that if the rear breather to the turbo intak is blocked off it will create a positive pressure in the crankcase under boost, potentially leading to leaking seals etc.
Your thoughts?

 

[saaber1]

There is no "boost" from the intake manifold in the bypass system. The old line form pcv to intake manifold is removed and the intake manifold port is plugged.

 

[Turbo_777]

Originally Posted By: saaber1
There is no "boost" from the intake manifold in the bypass system. The old line form pcv to intake manifold is removed and the intake manifold port is plugged.


I said "when there is boost (read pressure in the intake manifold) the PCV acts like a one way valve" There most certainly is boost acting on the Intake Manifold Gas Outlet pipe, it gets stopped by the PCV valve.

It is the plugging that I recon will cause problems in the long run as its that pipe that has a vacume in it when under boost conditions, so when you plug it the crancase has no way of venting and thus it will build pressure....look at the diagram...green arrows in particular.

 

[saaber1]

Originally Posted By: Turbo_777

There most certainly is boost acting on the Intake Manifold Gas Outlet pipe, it gets stopped by the PCV valve.


Please take the time to look closer at the bypass setup. There is no intake manifold gas outlet pipe. This is the last time I am going to say it. That line has been removed. There is no boost acting on the pcv.

 

[Turbo_777]

Yes yes, I was refering to the original setup....

Anyway you are detracting from the important part which is the gas outlet at the back...the one you have blocked up...before you have to mention that again.

By blocking that you are preventing the crankcase from being put under vacume when the car boosts and offer no outlet (UNDER BOOST)...so if you are doing a run from standstill to 240km/h you are going to build up some serious pressure in a crankcase that is designed to run in a vacume state....remember the PCV unit will not allow the fumes to vent through that blue hose to the exhaust when you are accelerating. You should at least run that pipe into the exhaust as well.

PM me your email address I will mail you the pics of my setup, Im happy if you post it on here...I just don't know how to post pics onto the forum

 

[saaber1]

What you said is 100% wrong. Either you really don't get it or you are just being a troll. Either way I am not going to waste any more time trying to explain it to you. Go start your own thread instead of cluttering up this one.

 

[Turbo_777]

This is the description for the TSI motor...much the same principle. Sounds like I was 100% correct.

Page 25...

http://www.arinahnell.com/other/vw/tech/20tsi.pdf

 

[saaber1]

I know you must feel that you have to save face somehow, but linking to a completely different engine with a completely different pcv system is really quite pathetic. Please go back into your hole, Troll.

 

[Gary Allan]

Hmmm...the crankcase is never under vacuum in your system regardless of boost or vacuum status in the intake. It relies totally on positive pressure in the crankcase to be vented into the intake "draft" upstream of the turbo ..essentially what excessive blow by would do in a crankcase that overwhelmed the PCV valve due to volume.

Is that essentially correct?

 

[saaber1]

Gary, if you are referring to the original posted bypass system for the 2.0 FSI, the crankcase is always under vacuum.

In the stock system, while not in boost, the vacuum from the intake pulls exhaust gases out through the pcv. This is done from a line from the pcv to the intake.

The bypass system uses this same principle but uses exhaust instead of the intake as the source of vacuum. In the bypass system I posted above, the bernoulli effect of the exhaust nipple pulls a constant but variable amount of vacuum to the pcv. The line from the pcv to the exhaust takes the place of the old line from the pcv to the intake. As a side note, the pcv acts as a "control" on the amount of vacuum being pulled.

Now talking about the stock 2.O FSI system while under boost: The boost is now present in the intake and you don't want that boost pressure going through the line from the intake to the pcv and thus into the crankcase. The PCV stops this and crankcase gases are "pulled" in pre turbo in the line out the back of the valve cover. As a side note, in cases where the stock pcv system fails, the pcv allows boost to "leak" in on the line from the intake to the pcv, causing an over pressure situation in the crankcase, usually seen by oil coming out the oil filler cap and a loss of power (boost) or mpg.

On the bypass system on the 2.0FSI posted above, there is no longer any line for the boost to go from the intake to the PCV, as the intake is capped. Similary the line out the back of the valve cover is also capped. So it is a very simple system which emulates the stock system when it is running in non boost, and gases are evacuated through the PCV under vacuum. The only difference is that the source of vacuum is different. The whole re-routing gases to the turbo when under boost is abandoned and is no longer relevant as boost cannot go to the PCV.

 

[Gary Allan]

Yes, we're on to the venturi vacuum thing. I've done it myself. I was just trying to figure where Turbo777 got his wires crossed.

 

[saaber1]

Originally Posted By: Gary Allan
Yes, we're on to the venturi vacuum thing. I've done it myself. I was just trying to figure where Turbo777 got his wires crossed.


Righto.

Btw, I appreciated your comments earlier about how if it was unregulated it could pull a high vacuum. Other people have mentioned this on other forums also. There is one guy on another forum that is running this setup without the pcv for a control and he is going to measure his vacuum and report back. It will be interesting to see how much vacuum it pulls with no regulation. Who knows, maybe it will be better with no regulation? It will be interesting to see anyway. I'll add that info to this thread when it comes in.

 

[Turbo_777]

Saaber1, clearly you are offended to behave in such a puerile manner.
Thus you have my unbridled apology for any offence I may have caused you; I hope you could assist me to understand this better as you did for Gay Allan.

Anyway more to the point:
Yes that was for the TSI motor which operates on the same principle as the TFSI and in much the same way, in fact the VW TFSI writeup is the same, and if you look back at what I said previously and what you said to Gary Allan, it’s all very similar. But let’s not dwell on that.

All I was endeavoring to understand is how your system compensates for the vacuum effect that would normally have been generated by the compressor on the turbo so as not to cause a buildup of a positive pressure in the crankcase.

I actually think your system is clever and the one thing I think would finally prove its validity would be (what I’ve been trying to get to in a roundabout way) to see if the vacuum effect generated by the Bernoulli effect of the exhaust nipple is equal or similar to the vacuum of the compressor intake under boost? Have you managed to take these measurements?

Regards
Bryce

 

[Gary Allan]

Quote:
Btw, I appreciated your comments earlier about how if it was unregulated it could pull a high vacuum. Other people have mentioned this on other forums also.


Well, aside from hearing a couple of others mention it (probably in hi-per or racing situations falling under the list of unintended consequences) I experienced it myself. I imagine it's engine specific if there will be an issue.

There are plenty of relatively cheap check valves with any range of cracking pressures/differentials that will act as vacuum breaks. These would need only to be bunged into the suction line. That's if some regulation/limit is required.

I don't race ..so that's just presented in a "if I wanted to that, here's how I'd go about it" kinda way.

 

[Gary Allan]

Quote:
vacuum effect generated by the Bernoulli effect of the exhaust nipple is equal or similar to the vacuum of the compressor intake under boost?


There shouldn't be too much in terms of vacuum on the intake side of the compressor. I doubt that it adds up to more than 10" of W.C.. It would mainly depend on the air filter restriction. Without a throttling point, there can be all the CFM and velocity in the world (well, practical world) and you won't develop a vacuum. The expanding gasses of the exhaust have so much more volume ..therefore more CFM ..and more velocity to produce a higher vacuum with the venturi effect.

Now if one were to install an extractor (venturi/etc.) facing into the compressor intake (downstream on the suction side), then you may develop a vacuum. Otherwise it would be termed a draft.

 

[saaber1]

Originally Posted By: Gary Allan
There shouldn't be too much in terms of vacuum on the intake side of the compressor.

You're right Gary. The measurements I have heard on this engine are about 1-3" Hg.