oil catch cans/tanks

[Gly]

considering fitting one to my car and there was quite a bit of oil in the pipe work of my car when i striped it down....

just checking that i will get the setup right.


i remove the the hose that connects the two rocker covers together?
use these holes to run to a catch can, (can with 3 fittings)

remove the hose that goes from the rear rocker cover to the intake,
and plug both holes?

and use a a filter or just leave the 3rd fitting on the can vented...

or do i use this fitting and run it back to the intake?

[Nick Mann]

I wouldn't do it like that personally, but I don't know which way is the best. I was going to fit one, but never got round to it. I was going to take the hose from the rear bank to the inlet pipework and run the catch can in to there. So front rocker to rear rocker as normal, then rear rocker to catch can to inlet pipe.

[Gowf]

The way nick has suggested is the way i have done it but then i had a one in and one out catch tank. You want to catch the oil vapour that is getting into the inlet air, as this can lower the octane of the fuel mixture. So by putting the catch tank between the rear rocker cover and the inlet pipe you are removing that oil vapour. If you have a 3 port one, then you could run a feed from both rocker covers and have one returning to the inlet. Some people dont return them to the inlet and let them breath through a filter into the air. I suppose it is down to personal preference as to how much oil vapour you want in your engine bay.
If you are getting oil in the pipe work, have you checked the turbos themselves?

[Kieran]

A word or two of caution....

The problem with catch tanks is if they vent to atmosphere, rather than back into the intake stream, it buggers up the PCV system and you'll end up with sludgy heads eventually.

On boost, the crankcase pressure increases and so the oily vapour is blown out into the catch tank and then into the engine bay. However, no *fresh* air is put into the engine - let me explain...

When off boost, the flow of air reverses.... Fresh, filtered air is pulled in via engine vacuum (the PCV opens) and it 'drags' fresh air in from the Y pipe that splits to the two turbo intake pipes. This fresh air is bought into the top of the engine and is drawn through, exits through the PCV valve and into the combustion chambers - helping to keep the engine clean of blowby grot.

I've seen a couple of VR-4s with open to atmosphere vents - it's not pretty. You do get some fresh air coming back in, but it's unfiltered and also it's not been metered by the MAF - not such a problem on boost as the PCV valve closes (in theory), but it does lean things out (if only slightly) when on partial or off boost.

Have a read of this for more info - very informative:

http://www.stealth316.com/2-krankvents.htm

[bradc]

Interesting info Kieran!

[Gly]

so best thing to do it use a can with 1 in and 1 out

and feed it back into the intake?

how well does this work??

do the cans usually have something in them to prevent the gases just passing thru the can and into the intake anyway?

[Kieran]

The cheaper cans don't normally have anything inside, however some of them have removeable tops so that you can fit some baffle medium, such as some reasonably coarse grade steel wool for the oil to condense on.