[Mk2] [Turbo] Catch Can Confusion

[Freebird]

Ok so I have been doing some research and not coming up with a definitive answer as to how best to fit a catch can. I’m running a 1996 Gen3 Turbo as an occasional road car and race car and the air intake to the turbo has become very sooty so I think fitting a catch can will be a good move. So after reading many opinions there is no clear correct way to fit, what follows is my reasoning, I would like to know what you think cheers:

The PCV valve opens due to the vacuum in the intake. true or false?

My understanding is that it does therefore if I remove the pipe going to the inlet, block the inlet side and vent the pipe to the crankcase through the catch can to atmosphere the PCV valve will not open. Therefore I need to remove the PCV valve and vent the crankcase to the catch can and through a filter to atmosphere.

So let the debate begin

[djpkins]

whts a PCV valve? it makes no difference at all to my rev 2 turbo whether I run a catch can and vent or recirculate...

[jimGTS]

Just vent the stock catchcan to atmosphere via a breather filter. Job done.

[garry goodall]

whts a PCV valve? it makes no difference at all to my rev 2 turbo whether I run a catch can and vent or recirculate...

the PCV valve is whats located on the rocker cover, is basically a one way valve that opens to vent blow by gasses when under boost.....

i think

[calum4492]

i thought u pcv valve was 2 allow the the hot and pressured air out of the crank casing

i think lol

[irish_dan]

It is. Doesn't have to be under boost though.

[Freebird]

You see my problem? No one seems to really know for sure.
The PCV valve (positive crankcase ventilation valve), as I understand it, opens when there is a vacuum applied from the inlet. In which case if you plumb it into a catch can with a filter it will never open as you have lost the vacuum supply. Can someone please tell me if this logic is correct?

[djpkins]

See what your saying there old fruit, but surely there wouldn't be a vacuum from "breather pipe exit - induction pipe inlet" anyway.
The valve you mention...on a rev3+ is a grey plastic plug in type that locates next to the filler cap....blow it and should shut, suck it and...lol...see....if that's closed then the breather pipe is just to relieve the pressure isn't it...bit like an exhaust.
Why do you want a catch can? I tried one on my rev2 to see if anything pooled up in it but it remained dry so I put it back to stock...I've seen quite a few with a wee filter on the rocker box and a blocked up intake but i don't see the point unless you have bespoke IC pipework etc.
It's like digging a hole to fill another hole and then finding something to fill that with.

[Freebird]

Well I want a catch can for two reasons.
1. don't want warm gasses going back into the engine
2. the inlet pipes are coated with soot from the oil vapourand I don't want that either

[jimGTS]

The rev3+ already has a catchcan as standard, there is no reason to fit another one in it's place.

As I've already said. Stick a filter on the stock catchcan, block the hole left on the inlet to the turbo and that's it. Cleaner ic pipes and inlet pipe.

[RyanRs]

PCV stands for 'Positive Crankcase Ventilation' ..there is no 'Valve' in the name. On the Gen3 + there is a catch can with 3 pipes, one is a vapour return (to the air filter box), the small bottom one is an oil drain for collected oil to return to the head and the small large pipe goes to the cam cover to collect vapours and release crankcase pressure. For this part i suggest detaching the pipe that connects to the airbox, block off the airbox end and attach a small vent filter to the disconnected pipe. Leave the other two pipes in place.

There is also a small pcv hose connected on the cam side of the cam cover, to a 1 way valve and into the intake manifold. This enables vacuum to suck vapours whilst off boost but seal once on boost. I suggest removing this hose completly, block off the intake manifold and put a filter on the cam cover end.

If you want an aftermarket catch can then remove the stock catch that i have talked about above, block off the small oil drain pipe, then run both the cam cover hoses to your new catch can. Still make sure you block off the inlet manifold PCV pipe (with the one way check valve) and block off the air filter vapor line. Make sure you get a Catch can with large ports as most have small 16mm (iirc) ports which will be too restrictive causing oil vapour pressure to leak at the dipstick and turbo seals.

[Steve Horrocks]

Exactly what Jim & Ryan say!

[Freebird]

Great thanks guy's, so bear with me here, what then is the gray plastic thing on the cam cover by the oil filler that the pipe attaches to is that not a valve? and the other pipe should the valve be removed?

Cheers

[djpkins]

"there is also a small pcv hose connected on the cam side of the cam cover, to a 1 way valve and into the intake manifold. This enables vacuum to suck vapours whilst off boost but seal once on boost. I suggest removing this hose completly, block off the intake manifold and put a filter on the cam cover end."

covered by ryan.

[Steve Horrocks]

There's a plastic 90 degree connector that pushes into a rubber grimmer near te oil filler cap. This is the line for the vacuum to the brake servo.

[Shmed]

There is also a small pcv hose connected on the cam side of the cam cover, to a 1 way valve and into the intake manifold. This enables vacuum to suck vapours whilst off boost but seal once on boost. I suggest removing this hose completly, block off the intake manifold and put a filter on the cam cover end.

Ryan, have you got any pics of this in place? I think I get it, but I'm not sure. If this also feeds the brake servo, won't that impact the brakes?

[nickg07]

There's also a hose without a valve that goes from the cam cover to the hot pipe, what's this for?

if looking from the back of the car to forward its on the left hand side of the engine,

[jimGTS]

That doesn't attach to the cam cover itself.

That's part of the a/c vsv. Follow the pipe and you'll see it goes to a part attached to the firewall then a pipe to the back of the inlet manifold

[Shmed]

The original thread was from 2011, I was just wondering because I was reading another forum and a guy was having issues where his brakes didn't 'bite' hard after long periods of acceleration (no vac). He found out that a check valve wasn't working between the intake and the brake servo. My brakes seem similar, they aren't great after long pulls, but get better, then get worse again. Just wanted to check I hadn't done anything wrong with the brake servo vac line.