Andy.F

Just a few thoughts on the need for and merits of an oil catch can and/or PCV systems

The original PCV (Positive Crankcase Ventilation)system does indeed do some good for the engine by ensuring the corrosive gasses are removed from the crankcase and replaced by fresh filtered air.
The Subaru system (MY93-96 - later cars may be different?) has two main phases depending on manifold pressure/vacuum.
Under manifold vacuum conditions (probably 99% of the engines life) there is a non return valve under the throttle body, which allows the 'blow by' vapours to be drawn into the manifold. The vapours are replaced from the vents on the cam covers, supplied from the inlet duct. This provides the circulation of air through the engine, prevents condensation, oil contamination and internal corrosion.
This is indeed a good thing and there is a strong case to retain this system if the car is a daily driver.

Under positive manifold boost conditions, the non return valve under the throttle body closes and the hot 'blow by' gasses (Note - 'blow by' tends to be a cool vapour at low power but a hot gas at high power) are re-routed via a 't' piece to the intake duct for reconsumption by the engine. The cam cover vents may also vent out during this phase.
This is where you can get oil suspended in the gasses finding its way into the induction system......this is a bad thing ! The oil coats the intercooler, reducing efficiency and causes premature det due to lowering the octane of the fuel.

It is possible to 'catch' the suspended oil in a 'catch can' This is a reservoir deigned to reduce the velocity of the gasses, allowing the oil to fall out of suspension. The oil collects in the bottom of the can and the oil free gasses carry on to be either reconsumed by the engine or vented to atmosphere. The catch can will ideally intercept all 3 vent lines although the main culprit on the Subaru would appear to be the central crankcase vent.

The return of gasses from the catch can is also the subject of some debate. If the gasses are reintroduced to the intake system then you are asking the engine to burn an oxygen free mix ! ie you are reducing slightly the amount of oxygen fed into the engine, this can only mean less power. I personally prefer to vent to atmosphere and block off the return to the intake system. There are concerns that this is not very 'green' however the vented gasses are just of the same constitution as your exhaust gasses (assuming you have a decat exhaust)

The EGR (Exhaust Gas Recirculation) system fitted to some cars for emission controls is a different thing altogether.

Depending on where you lead your vent it is possible to get a hint of fumes in the cabin. This is however unlikely as the only time you will vent via this route is during positive boost pressure.....the car is unlikely to be sitting still for very long !!


I have taken my system a step, actually 2 steps, further.

I have removed and plugged the PCV non return valve to eliminate any recirculation of gasses whatsoever. My reasons for this
1 - I don't need the corrosion protection as my car does not get used for short runs or town driving, every outing is a real 'toasting' !! I also change the oil frequently.
2 - I found that I was still getting some oil in the intake plenum, I think this was residual oil in the vent lines being drawn in when I went from boost to vacuum (ie each gear shift) This was giving me some transitional det.

I also bypassed the catch can ! I found that leading 3 bigger bore pipes from each of the breathers, direct to atmosphere, reduced the gas velocity to such a degree that the oil fell out of suspension before getting up the pipe My vents now route up from the take off points, over and down to the anti roll bar area. Once again, as the gasses are basically exhaust fumes then there are no environmental issues.......It is however very 'engine friendly'

Andy

Pavlo

Bored today? Too much time on your hands?

Just wondering....

john banks

Well I left the PCV valve in place and vented the central crankcase line into the can rather than the inlet pipe. The other side of the can has a vent line. All of them and the can are dry at present, which in a way is a good thing but means I might have rearranged my finger and have hassles mounting this expensive coke can somewhere for nothing I have not vented the rocker covers yet.

Bob Rawle

Good post, the later cars are the same as the early cars, the only change I have made to the above is to leave the rocker cover breather in place and install a second PCV valve in it, this then allows air to be drawn into the rocker cover space to ventilate the crank but prevents and pressurised oil film escaping back into the air intake, I originally had the crankcase vents and head vents teed together into my catch can but started to suspect that this was setting up a "double suction" type event which was not good. So now my setup is crankcase to inlet manifold via PCV as normal, crankcase to catch tank and rocker covers to air inlet pipe via second PCV valve.

I get no oil film at all into any part of the intake system and, since the PCV valve closes at the slightest pressure in the manifold, then I get no oil film entering the engine under boost.

Bob

Andy.F

Good idea with the second pcv valve Bob

Paul, I had an email asking about catch cans, just thought I'd copy my reply on scoobynet in case any one was interested.

Andy

David_Wallis

what does a pcv look like?? I thought the pipes just went direct and the 'reason why' was called pcv??

Its probably too early for me..

David

john banks

Looks like a bit of nasty Subaru black plastic connecting three black hoses together on mine.

Andy.F

PCV is the name for the system, the PCV valve which I think you are referring to David ? is a steel valve screwed into the intake plenum, just below the throttle body (original one that is )It is a one way valve that allows crankcase vapours in to the manifold but stops the pressure escaping during boost.

dowser

Thanks Andy,

I guess my email prompted this

I'm still undecided though - nice looking re'routing of pipes to bottom of car, or bodged up catch tank system.

My car has just gone from being a daily driver, but it doesn't spend it's whole life being caned either...and am concerned about negative effects over time of having this crap lurking in the engine.

I'm off to look at the system to try and get a better idea - especially Bob's suggestion

Richard

David_Wallis

cheers andy... I know which you mean...

David

Mr J

BOB So you attached the crankcase to the can and what about the cans second attachment ??
Should it only vent to the air or ???

Were do you get hold of a second PCV ??

Regards
Jan

Mr J

BTT

Bob Rawle

vent to air via a K & N crank case filter ... pcv from your dealer maybe ..

Bob

Mr J

Thanx Bob

Cheers
Jan

Adam M

can someone come up with a graphical representation of what I should do breather system wise?

Have been giving this some thought, but hadnt considered providing a fresh air vent to replace that which is coming out.

Intended to do away with recirc system and block of all holes in inlet tract and inlet manifold relating to oil breathers as well as fitting a catch tank.

Dont want to be dripping oil on the road!

plus dont want to find pools of oil under car as they may make me paranoid about my newly built engine.

Mr J

Yeah I agree with you Adam, it sure would be nice to "see" what to do

Jan

dowser

Just to bring this back to life

Fitted the Cusco solution over the xmas period...along with a new inlet pipe. So far I've just done the crank line.

While the Cusco is nice and shiny, it's a pretty ill thought out bit of kit IMHO. A 3rd input/output would have been nice....and nowhere on the box does it mention the Impreza...

The bore of pipe provided is way too small to easily attach to the crank 3-way T-piece hiding just under turbo inlet....I didn't do myself quite as much damage as JB did (you'll have to do a search ), but on a scale of 1-10 I'd give the inlet pipe/catch can a '27'.....

Bob - the stock PCV valve seems to screw into the manifold (haven't removed it yet - but I do have a spare manifold now ), did you use an OE valve for your rocker cover's 'one-way' mod? And does the filter you stuck on the Cusco outlet get gummed up (I'm currently returning mine to inlet....thought I'd try the green approach first ).

Cheers
Richard
PS: I installed my tank on the turbo side turret - seemed best fit, but maybe only on LHD cars?

john banks

Mine still has no oil in

dowser

Lol! I wouldn't like to think getting that pipe on was a waste of time..... Old stuff was all coated, and i/c needed a clean again. It's coming from somewhere...

Richard

john banks

Maybe high boost reduces my blowby - not Somehow my intercooler pipes are clean maybe by magic, maybe the oil mist goes out the exit pipe Andy F style? Don't know, but with everything the timing is pretty good.

Andy.F

Nice pics John Did Santa bring someone a digi camera

john banks

Yes having a little play. Shows up the dirt quite well doesn't it

Andy.F

Scoobynet server >>> prepare for overload

dowser

Jeez - I'd be embarrased to show a piccy of my engine bay....you could eat your dinner off yours

Richard

john banks

Using my own webspace for the fotos. I was in two minds whether to put the piccies up since I thought it was dirty - well look at some of Alan Garrod's pictures and you'll see what I mean.

AlanG

Like this one??





Alan

EvilBevel

That's not an engine, that's an E.R.

[Edited by EvilBevel - 12/27/2002 4:52:44 PM]

NINJA

alan what intercooler are u running or is that custom pipework it looks like aps but better

Tone Loc

iTrader: (1)

Correct me if im wrong but that look to be a Hyperflow intercooler.

Tony.

AlanG

Correct Tony, it's a Hyperflow intercooler.

Had it on a year now, no issues with pipework, which I believe some folks have had with the APS.

Checked for pressure drop the other day ( due to other work ongoing at moment) and pleased to say it's negligible, maybe max 1/2 to 1 psi?


Alan