(Senior Member)
11/30/18 04:27 PM
Inline pcv route

I'm trying to clean up the hoses under my hood.

If I were to put a 90 barb on the top port connected to a T on the side of the valve cover and then a bigger barb and hose going to my catch can, what size hoses would be adequate to vent the system property ?

(Carbon Fiber Cage)
12/01/18 04:56 PM
Re: Inline pcv route

There's a little more info needed for something like that. Typically, there is no such thing as "too big". If you're stock boost with a stock ring gap engine, you could probably get by with 3/8"(#6) hoses. If you have a looser setup, I'd say 1/2(#8) minimum, preferably 5/8" (#10)

(Senior Member)
12/08/18 05:42 PM
Re: Inline pcv route

ok, Yeah So this is what Was going for. and the sizes I settled on.

small hose 12mm id
large hose 16mm id
t is 3/8" npt
valve cover opening is 1/4" npt

16mm hose will go to turbo inlet pipe.

(Senior Member)
02/16/19 11:44 AM
Re: Inline pcv route

Is there a problem not using the intake manifold and a check valve for a second source of vacuum?

I'm being told that the using only the nipple on the pre-turbo pipe is not adequate during idle, cruse, and quick throttle close.

How much of an issue and what symptoms will I have?

I kind of screwed my self because I mounted my fuel hoses very close to the intake manifold pcv orifice and don't know if I can still fit I nipple fitting in the stock location.

I would really like some experienced opinions before I charge all these systems. I don't want to cause weird driveability issues became I will most likely never be able to figure them out at that point.

(god hates stupid people)
03/01/19 06:00 PM
Re: Inline pcv route

I'm not running off the intake manifold anymore, because in general the PCV starts having an issue with big boost levels. I have a sealed can, both lines go from the VC to the catch can, it's baffled, and then I run to the turbo inlet. I don't really see how the vacuum at the compressor is going to be significantly lower than what's in the intake manifold since all the air going through the manifold is first routing through the turbo. Perhaps someone smarter than I can comment on that, but in the end, I don't have any way to really revise it so I'm not going to worry.

If it helps, all my lines for the catch can are -10 (iirc that's .5" ID)

(well bread and nobly conceived)
03/07/19 03:38 AM
Re: Inline pcv route

In case anybody hasn't read it, here's an excellent article on the PCV system in general.

Under the normal configuration, when the IM is under vacuum, air is drawn in from the intake snorkel through the left facing port, through the valve cover, and into the IM through the PCV valve. This steady flow of fresh, metered air, keeps the crank case well ventilated. It also explains why PCV systems can affect idle stability, because the air flowing through the PCV is in addition to the BISC and ISC, so changes to the PCV must be compensated with changes to the BISC setting. And, as we know, under boost, the PCV closes and the flow direction reverses, so that blow-by is expelled into the pre-turbo intake and ingested through the engine. This is where your catch can or oil-separator come in, to collect oil during flow reversal under boost.

Depending on the application, an alternative configuration might be a good idea, but in general there are two problems with eliminating the IM vacuum source. First, the vacuum in the pre-turbo intake track is relatively weak compared to the IM, so you don't get nearly as much suction under normal driving conditions. And second, the VC is no longer 'ventilated', in the sense that there's no fresh air being drawn in. The slight vacuum from the pre-turbo inlet will relieve any pressure built up from blow-by, but there's no way for fresh air to get into the crank-case. As such, this configuration is good for relieving high crank-case pressures caused during heavy load, but generally does a poor job of keeping the oil clear of steadily accumulating hydrocarbons and other combustion byproducts. Hence why it is recommended for 'race-only' applications where you change the oil often and spend relatively little time under 'normal operating conditions'.

(both buccal and lingual)
04/04/19 10:27 AM
Re: Inline pcv route

Great article and explanation on PCV routing.

How much would elminating the side of valve cover to pre-turbo breather effect idle/driveability? From the article this appears to be purely crankcase ventillation effects, yes?

Also, a catch can in the PCV loop should not have a breather filter on it, correct? I believe this is an obvious "correct" answer but I'm asking because I had purchased and installed a RRE catch can in I think 2000 or so that has a breather filter on it. Don't think this is a good thing.

Essentially my PCV system as it sits is all messed up.


(well bread and nobly conceived)
04/04/19 11:28 AM
Re: Inline pcv route

No part of the PCV system should be open to atmo as this will lead to unmetered air being ingested through the PCV valve.

The pre-turbo-to-side-cover port is for ventilation when the IM is under vacuum. But under boost, the PCV valve closes and the pre-turbo port becomes the relief valve for positive crank-case pressure. Blocking it off can cause dipstick blowout and potentially an engine fire.

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