silent running

I posted a different thread about my broken OE inlet pipe (MY98 WRX) but after a bit of mulling it over, I've whittled it all down to this:

Is there any downside (performance, longevity etc.) to having the breather system 'closed' when on boost and working as standard the rest of the time?

Off boost, my breather system will work as Subaru intended - vapours are pulled into the manifold through the PCV, via the crankcase, from the rocker covers which are supplied by metered/filtered fresh air from the inlet pipe. Only mods are a one way valve to allow air to be drawn out of the inlet but not back in, and a one in/one out catch tank just before the PCV valve.

On boost, the PCV will shut as it's supposed to, as will the one way valve in the side of the inlet, effectively closing off the breather system entirely. There is no longer any direct crankcase-to-inlet pipe connection. The only route for oil vapours is via the PCV valve when the manifold's drawing a vacuum.

I've kept it as short and concise as I can, but I don't know what effect having the breathers closed on boost will have e.g. oil pressures, ring seal, power developed etc. If there will be no difference, I'll leave the system as described above.

ZEN Performance

on boost is when you need the engine to breath the most, block them at your peril. Better to route them to atmosphere so you're not ingesting air from the crankcase into the inlet.

silent running

That's the problem Paul; I *can't* currently route them back into the inlet because the plastic port snapped. No other option, apart from closing the system on boost, seemed that it would leave the AFR the same i.e. there would be an imbalance between what was going in through the rockers from the inlet and what was being vented out through the crankcase.

Let's say I leave the crankcase breather hose open, I know I get a slight vacuum I can feel at idle, presumably this is from the open PCV pulling in partially from the crankcase and partially from the open air i.e. unmetered, unfiltered air. Hence AFR goes slightly leaner whenever there's a vacuum at the manifold? At a guess, on boost there will be positive pressure in the crankcase which wouldn't be a problem as it will just vent out.

Correct, or not?

ZEN Performance

aaaaah I see.

Route breathers to atm, preferably via a catch can, and block the ports on the inlet. Do all the breathers, except perhaps the PCV valve on the manifold, but personally I would do that too. Then you get less dilution of inlet charge with exhaust gas from breathers, reduced carbon buildup, reduced contamination of ingoing petrol, and if you're catch can works well, I would say reduced loss of oil.

If you block the breathers at the engine end of things, expect things like blow turbo seals, crank seals, cam seals, reduced power, reduced MPG and generally poorer running on and off boost.

Paul

silent running

Very interesting...fuel economy *has* actually dropped from 26 to 23mpg since having the crankcase breather blocked up. So let me get this straight once and for all; the best solution is all or nothing - either keep it green, sealed and fully recirculating, OR open up all the breather ports to atmosphere via a catch tank.

Seeing as I can no longer keep it fully 'green', I might as well do as suggested and block off both the inlet pipe connectors and route rocker cover and crankcase breathers into a catch tank and then to atmosphere.

Last questions then:
Can my one in-one out catch tank be used to tee all the breathers into one side of the tank?
If so, should I just stick a breather filter on the other side of the tank, or run it down a hose under the car?
If I keep the crankcase-PCV line connected, perhaps with a catch tank of its own, will this lean the AFR when off boost and if so, will it be negligible to performance?

I just like to understand things properly before doing them! :-)

rigga

iTrader: (4)

I run all breathers to a one in one out catch can,teed pipes together before the can and just run the exit pipe to lower level of the car..... just get a lot of water build up in the can rather than oil,but figure its better out of the engine than in........

silent running

OK I'll go and get the bits then. Cheers!

silent running

Latest news, and it's not good. I just started pulling the engine bay apart again as I'm still not sure the 'modified' inlet pipe is on properly and need to close up both the breather ports on it, route all the breather pipes around, remove the PCV etc.

Anyway, I was horrified to find that the inside of the turbo was coated in fresh oil and it had leaked out of the compressor outlet. The turbo to intercooler pipe was literally dripping with it, not just filmed but sitting in pools at each hose joint. Presumably it's coated the FMIC too. The exit side of the FMIC seems dry as does the inlet manifold.

Now apart from resigning myself to the fact that I'm gonna have to replace the inlet pipe completely, have I busted the turbo oil seals as well somehow? I still can't see how blocking the engine breathers while on boost (how I did have it setup for a day or two) can affect the turbo seals?

Is it that the crankcase pressure would have had nowhere to go so pushed through the turbo's lubrication system somehow? And if so will this have been a temporary problem or something that is now knackered for good until I pull the turbo off and fix it?