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View Full Version : No Vaccuum For PCV In Intake Before Turbo



alltracman78
10-02-2011, 03:30 PM
Anyone else run into this?
I've got absolutely no vaccuum in my intake before the turbo, so I have zero suction in my PCV system. It's [at least helping to] causing a nice smoke screen if I boost at all.

Larger turbo, no AFM, just an HKS foam filter.
The intake is about a foot long, so it's pretty short.
I'm guessing there's not enough of a restriction at the end of the intake so I don't have any pressure drop, but I'm curious if anyone else has had this problem.

The engine is fine, pulling ~ 18 in/hg, and the turbo spins/spools, so it's not that.

Sang
10-02-2011, 03:32 PM
There is little to no vacuum in that line to begin with on a gen2. Mine has been vented to atmosphere for the past 4 years now.

alltracman78
10-02-2011, 04:37 PM
Any suggestions?
I don't want to make a smoke screen everywhere I go.

I've never had this problem before.
To be fair I've never checked for vaccuum in the intake before either, but I've never needed to.

I also didn't have this problem when I was running my RC stuff, but as soon as I got rid of the AFM it got really bad.

How well do other turbocharged cars pull a vaccuum there?

alltracman78
10-02-2011, 04:44 PM
Just for the record, I actually hooked up a vaccuum gauge [Snap On diag gauge, not a cheap boost gauge] to the intake. It stayed at zero, even under boost. The needle didn't even twitch.

If I can fit the AFM back in there now I may do that, I'm curious what the vaccuum will be [if any].

Luni
10-02-2011, 06:29 PM
Gen 2s have 2 sides to the pcv system. The side at the intake manifold has vacuum on it unless you're boosting. If you're boosting, venturi effect draws shit out the intake side to be reburnt. There isn't going to be any vacuum in the intake. The turbo can't move enough air through that tube to create anything you can register. I can't see how having an AFM or not in there is going to change anything. Check for vacuum at the line attached to the nipple on the valve cover on the passenger side if the engine at idle.

temperacerguy
10-02-2011, 11:18 PM
well, there is a small vacuum in the intake between the turbo and the filter... but as I said, it's small. Like Luni said, the main way the PCV system draws through the PCV is through venturi...
(I have no idea what the "other" side is..... I think he may be including the EGR system in, but on the Gen 2s there is only 1 PCV tube/system)

Now, when most people re-connect their PCV system to the aftermarket intake, they typically just weld in a pipe at a 90 degree angle and call it a day. This WILL work... just not drawing as much venturi as the restrictive Stock system. The stock system is just a slash cut pipe in the intake.

Funny part is I just addressed this issue when helping a friend building a custom twin turbo GTM (custom LS powered mid-engined kit car), and we built the most efficient PCV system we could. Here are the diagrams...

Here's what most do:
http://i236.photobucket.com/albums/ff73/temperacerguy/PVC1.png

Here is what factory is like:
http://i236.photobucket.com/albums/ff73/temperacerguy/PVCslashcut.png

Here is the optimum balance between venturi and restriction in the intake:
http://i236.photobucket.com/albums/ff73/temperacerguy/PVCoptimal.png

Now, with all this being said.... I do not think this is your problem... It sounds like your rings are starting to go.... time to run a compression check, if that comes back fine, start looking at your turbo seals.

alltracman78
10-03-2011, 02:15 AM
Rings should be fine, I did a compression check when I got the car and it was ok.
The turbo seals are starting to go, but it wasn't blowing nearly as much smoke as it does now that I changed the intake [went from RC AFM/K&N filter to HKS pod filter]. Later on tonite I hope to swap the AFM back in and I'm going to measure the vaccuum; I'm curious if there's any difference.
Factory on these is actually the last setup you drew, I hadn't thought about it like that, that's a good idea. Thanks :)
Oh, the second "side" to the PCV that Rob is talking about is a small hose running from the TB to the valve cover. It's a small port right near the oil fill.


Gen 2s have 2 sides to the pcv system. The side at the intake manifold has vacuum on it unless you're boosting. If you're boosting, venturi effect draws shit out the intake side to be reburnt. There isn't going to be any vacuum in the intake. The turbo can't move enough air through that tube to create anything you can register. I can't see how having an AFM or not in there is going to change anything. Check for vacuum at the line attached to the nipple on the valve cover on the passenger side if the engine at idle.
I know how the shit works. :) It's just not working correctly with my current setup [it doesn't seem to be anyways].

Technically I don't think this is the venturi effect. The venturi effect is created when you narrow a portion of a passageway.
There's no narrowing of the passageway [intake].
But I know what you mean. :)
As far as having no vaccuum in the intake at all I would assume there should be at least a small amount. I have ZERO, even while boosting.
The air rushing past the hole[s] should create some small vaccuum in them, as it should pull air out.
Having a filter/AFM will work like a choke in a carburetor. Wide open short fat intake tube will have very little pressure drop between the turbo and the outside air. If you add restriction to the other end [and maybe lengthen the tube] it should create a pressure drop in the tube, just like a choke does on a carburetor. Hopefully this will help pull air out the PCV, just like a choke helps pull extra fuel through a carburetor.

I'll try that other setup, I just can't do it right now.
Hopefully this winter I can sort that out.

Luni
10-03-2011, 05:15 AM
Ive never once measured ANY vacuum in my intake. I have hooked a boost gauge up to it and even when full stock Gen2 (with just a filter), I never got that needle to go anywhere other than zero.

alltracman78
10-03-2011, 03:07 PM
I think you're right about that. I put my intake back how it was [RC AFM/K&N filter] and still measured zero vaccuum.
BUT, I didn't see any smoke last night.
I won't say that was the problem yet, I need to drive the car more to be sure, so we'll see on that.

I wish I had a way to measure airflow in those hoses, I'm really curious about that now.

andy
10-05-2011, 04:52 AM
There wont be any vacuum, just airflow. poking the tube down into the airstream will cause that tube to have a vacuum. However its small. The pvc on my 2jzgte has it piped into the post tb section of the intake.

alltracman78
10-11-2011, 07:51 AM
Just wanted to update this for FYI.

Yes, there is no vaccuum in the intake before the turbo.
I checked with my AFM installed, still no vaccuum.

BUT, once I installed the AFM back in the smoke is gone.
Even after 1/2 hr hiway driving/boost it still doesn't smoke.

SO, the less restrictive intake WAS causing the majority of the smoke.
The turbo is going, but the intake made it much worse. I guess I'll live with the AFM installed for now.

Luni
10-11-2011, 03:11 PM
So, break it down.

Youre saying that the bigger the intake you run, the more smoke you are going to get?

alltracman78
10-11-2011, 06:18 PM
I don't think necessarily bigger; less restrictive should be more accurate.

If your turbo isn't already starting to leak I'm assuming this wouldn't be an issue, but if the seals are on the way out it may cause a problem.

Sang
10-12-2011, 03:07 AM
Have you tried driving around with the vent open to atmosphere with the new intake? If not, then please do and report back.

Because thus far, what you're stating doesn't make any logical sense to me. If there's no vacuum then there's no vacuum...I don't see how a better flowing intake is causing extra pressure at the turbo seals than otherwise. The only way I can even see a possibility is if your new intake is poorly designed and as airflow is going to the turbo some of it is being caught up by the crankcase fitting. This will prevent the crankcase from venting, and also cause a slight pressurization in the crankcase.

alltracman78
10-17-2011, 01:53 PM
I'll keep this updated, I don't always have time to check this stuff right away.

I'm going to get pics of all this stuff so we have a record of it.

alltracman78
10-17-2011, 03:28 PM
Here is how I have the intake/PCV right now.
The AFM is just sitting there, I'm not using it.
No catch can, just tubing and a elbow.

I do have some smoke, but I don't get it unless it idles for a long time [say over 10 min].
It will smoke a little sooner if I boost to like 8 PSI and idle it soon after.
But hiway driving with low boost won't cause it to smoke within 30 sec like the other intake did.

http://i1198.photobucket.com/albums/aa460/alltracman78/IMG_0768.jpg