Oil Catch Can Question

[phat_levin]

i recently put an oil catch can on my car. it is the 2 inlet with breather setup that everyone on here seemed to think would be better. now i was discussing this with a mechanic friend of mine, and he was saying that the way it is set up now means that the air intake is not sucking the air out of the crank case breather under load. so would this mean that there is now more pressure in the crank case? and would that explain why i have had to change the oil filter housing seal and the o-ring where the dip stick goes in due to oil leaks appearing?????

[phat_levin]

ok so is everyone stumped or is this theory a crock of shit car is silver top 20v by the way.......

[Punter]

The idea of not using the intake to evacuate the crankcase is to stop oil/oil vapour from entering the intake.

The way you have it setup now stops this, if you still have alot of crakcase pressure you may need more vents. (thats normally a sign of a worn engine)

Also, anyone feel free to correct me.

[phat_levin]

yes but what im saying is before i touched it the crank case breather was connected to the intake, so when the engine was sucking air in would it not have been sucking air out of the crank case at the same time? now the crank case has to empty itself by its own means..

and yea 190,000kms would probably be classed as an old worn engine

[Emperor]

The pressure should be enough to release the gasses shouldnt it?

[phat_levin]

well thats what i thought, but this mate of mine reckoned otherwise

i did think it was mildly coincidental that i had a couple of oil leaks after setting up catch can tho.....

[jondee86]

On the AE92 16 valve engine, the cam cover vent looks like it
hooks straight into the manifold. But it is actually ported internally
to a vent in front of the throttle plate. So it only sees intake vacuum
which is way less than manifold vacuum.

It has to be done that way because otherwise you can't get a decent
idle with what amounts to an uncontrolled vacuum leak into the
manifold. I don't know about 20 valves, but most engines I have
looked at vent into the intake ducting.

As already said, if your engine is getting tired, you will be getting more
blowby and more internal pressure.... and leaks.

Cheers... jondee86

[Loudtoy]

Are you dead certain you didn't have any leaks before you hooked up the catch can.
I did this on my old 20 valve and it was fine, ran for ages like it and apart from filling the catch can 3/4's full by the time it was due for an oil change every tiem it was fine. If i wanted to avoind the catch can being as full as it was i would have put something bigger than a 500ml can in there but it didn't worry me and it wasn't used in motorsport except for the odd drag meet so i didn't have to worry bout minimum size.
And unless your motor is absolutely stuffed with hardley any compression and massive amounts of leakage past the rings you won't have any problems with the crank case presurising any more than it did before. I'm not entirely sure how much vacume you get in an intake of a 20v but i wouldn't expect it to be all that much once you factor the intake pipe size then think that the vacume will be uniform no matter what the pipe size and suddenly thin that hey, nothing contracts when under full throttle and the intake pipes are pretty easy to squash or constrict under vacume.

So short answer is his throry is a crock and for the long answer read above

[phat_levin]

ok i can sleep easy then thanks

[Mr Revhead]

yeah, i run my 182k ae101 levin with that set.


you do have a vented can dont u?

[phat_levin]

of course

[Mr Revhead]

just checking

[shiz]

Does, anyone have a photo of where the catch can would go on a 20V silvertop. Thanks

[flygt4]

i run mine the same with no issues. revved it to 8500rpm around manfield at times with no real ill effect. was less than 5mm in the catch can after too. i have a reasonably fresh engine tho

[SUBARUCONVERT]

When your at full throttle there is no vacume in the intake manifold so it cant really draw from the crankcase at that time.

[big_boy]

have you still got the vacume line hooked up some were

[frost]

why is your friend thinking the oil catch can is for crank case?? its for the crank case?? did i miss something or am i wrong in thinking its for the head. as in head oil vapor catch can or oil overflow can as also known by ppl who race blue top 4age's . ok yes some crank case gas will come up the oil ways and the stem seals. but there shouldn't be much. if theres lots of gas in the crank case then its time for engine rebuild/refresh. because that means your rings are stuffed and compression is getting pass them and into the "crank case"

is your oil dip stick jumping around while you rev the engine? if it is then thats what youve got stuffed rings.
and oil leaks will come soon after. the gas has to get out somehow.

in a perfect world all the gas world go out the exhaust ports but thats not the case, some will gets pass and mix with oil and water and together they form sludge like vapor that is not good for re-use in engine's full stop. so thats why we use a can to trap it and not let it back in the engine

automotive theory says best is ZERO pressure in both crank case and head. for two reasons
1, easier for oil pump to circulate oil around engine.
2, less resistance for moving parts to complete there cycle. eg. zero crank case pressure = zero resistance for piston's on down stroke..

there is no external crank case breather on the 20v engines. there is only two head outlets, one on the inlet side of head and one on back of head. in my mind the high revving engine should have a crank case breather just for that little bit extra bit rev happiness. sorry im off topic, i'll stop.

[RedMist]

The head is connected to the sump via oil galleries. As such venting the head indirectly vents the crank case.
Rather than 0 pressure if you can create a vacuum, like in excavator or dry sump systems, you reduce the aerodymanic friction of your rotating components further.
As such I believe in the stock recirc system.

[big_boy]

if it was me i would go for a non vented catch can in the middle of the stand vent lines that way it catches the oil but the air for the stand car system is still alowed to flow causeing a vacume & running a netive crank case pressure like the cars come out the factory with

also in relation to the question check your PCV valve i would supect its faulty

[Mr Revhead]

the problem with a feed back system, is you still get vapours in the inlet, the result of that is a lowered octane of the fuel/air mix. 20vs are very sensitive to that