Crankcase ventilation

[zep]

Yoodle.

I'm fiddling with a few things in the engine compartment and am moving my oil catch can so have been looking for a new one, square one to sit up on the fire wall. It seems that most of the square ones have no place for mounting a breather filter, or have two in/outlets near the top so you could probably run one line to it and a filter on the other.

So I looked into this. Some people frown upon venting to the atmosphere, saying that you need the vacuum from the intake to draw out the oil vapour and keep the engine (rings especially) in good knick. I've also read that oil vapour can reduce the octane rating of your fuel. Others say that venting to the atmosphere is fine and is better for your engine.

I'm tossing up between running one line from my rocker cover to an oil catch can, with a breathing filter on the top. The other option is to run one line to the catch can, and another out of the catch can back to the intake. What would you do? And if I take the second route, should I plumb it straight to the plenum? Before the throttle butterfly? Before the turbo( although who wants oil in their turbo/intercooler)? Also, if I change to the 'routed to intake' setup, will this fuck with my tune?

Cheers boys.

[Unclejake]

If in doubt - vent. Vent it everywhere you can.

The myth of dry sump vacuum on a sealed crankcase boosting horsepower (by less atmospheric pressure under the piston crowns) only works for drag motors. A circuit car will spew oil everywhere unless you vent it once the oil gets to proper temp

Vent

[kpr]

if plumbing back, you need to plumb back before the turbo. else you will pressurize the crank case on boost

most factory systems will have 2 pipes. one from the cam/rocker cover straight to air intake (before turbo). then another from cam/rocker cover to intake after throttle/s,with a pcv inline with it. the pcv (basically 1 way valve) lets the inlet manifold vac suck down on the crank case under vac. but stop the crank case pressurizing when on boost.

ive ran catch cans with filter on top. but most of the time you end up with a filter clogged with oil, so breather system is junk. a well baffled catch can may help the cause. on the kp i just run a big breather pipe from cam cover to catch can, the another from catch can to atmosphere unfiltered.

changing it around shouldn't affect you tune much, unless its breathing pretty heavily and you plumbing back to air intake. wouldn't hurt to get it checked for knock though

[Unclejake]

Oil contamination of the breather filter can 'probably' be reduced by putting an S in the breather pipe, so that there is a low point for the oil mist to pool in. Getting that pooled mist back into the sump may, or may not be worth doing.

[Unclejake]

KPR, I am really interested on your connection between CV and potential knock. Could you expand?

EDIT: Serious question and not for a moment a challenge.

[zep]

Cheers guys.

I'll just keep on venting to the atmosphere then. Will a catch can with the entry into it and exit to the atmosphere on the same level be ok instead of a pipe with an S-bend?

Edit: just saw this

[bubblegoose]

rule= atmos only breather requires more regular oil changes due to water build up?

heard that somewhere

[Steelies]

one 'pro' reckoned the valving or whatever magic is in my 4age's breather cam cover is fucked as i was getting squeaking seals at high vacuum, so i went to a can/breather

it has a surprising amount of air movement and water in the can, not sure what the norm is though..

[Testament]

Cheers guys.

I'll just keep on venting to the atmosphere then. Will a catch can with the entry into it and exit to the atmosphere on the same level be ok instead of a pipe with an S-bend?

Edit: just saw this

that looks really small. There is some MSNZ rule for the sizing too, I know a 2L engine has to have a 2L catch can but can't remember they rest of it.

also with the outlet right next to the inlet thats not really going to remove much of the oil from the air unless in has some internal baffles.

[Raizer]

I've always run sealed catch cans with a PCV on my cars, they really need to be baffled to work properly in my opinion.

Twin cans can work really well too

"catch can 1" is hooked up to the cam cover.

[CaMpylobacter]

I ran atmo can for ages. no problems with oil going evereywhere. get lots of moisture but probably no more than usually fired back into the manifold. you just notice it with a catch can as it condenses.

[rayban]

Is pulling vacuum from the exhaust an option?

[CaMpylobacter]

^ if you wanna do motorsport stuff you're not allowed to, apparently. that'd be a sweet idea though. A guy I know looked into that to make it so he could run without his breather going to the intake, but still have crankcase under vaccuum for 'windage' reasons (he reckoned.... guy is OCD as anything.... KK will back me up on that hah).

under msnz rulings you're not allowed to do so. on a roadcar you could do what you want though and it'd be a pretty sweet idea IMO.

[Simon]

My first idea was try get some sort of vac from the exhaust also.

But the manifold / exhaust must be under a lot of pressure so trying to get any venturi effect may be difficult?

All mine just go to atmo. The Alto starts running bad if I have it going back into the top of the carb. HAd to do a road side de-gunk one time as it goes into the secondary throttle and I often don't use that to get 5000k per litre.

[CaMpylobacter]

^ breather mods are a must for altos hah. used to run mine open for same reason. had a sweeeeeet k&n breather filter on there hah

[Ogre]

^^lol, remember that from high school, was oh so sweet

[RUNAMUCK]

I wouldn't run a system where the intake rebreathes the blowby. Its non performance enhancing, and as the inside if you IC gets coated in oily slime it reduces it's ability to conduct the heat away from the boost and back into the atmoshere.

I run a custom made catch can, which has a baffle in the top to discourage stuff exiting via the breather cap. (Used to run a really unhealthy motor that was all blowby and condensation)

But a word of caution, mount it as far away from your heater cowl as possible. Nothing worse than when your engine starts to breath hard, (Like when you're giving it death) and the sickly reek of bloyby comes in the cabin. Make you feel quite ill.

[kpr]

KPR, I am really interested on your connection between CV and potential knock. Could you expand?

EDIT: Serious question and not for a moment a challenge.

just as zep said in op. oil contamination in the air fuel mix. but i would think the amount of contamination would be too small to have much effect. unless the engine is allready rooted and really pumping it back into the intake, im just a bit picky after previous turbo cars that ive kinda tuned on the edge to get the last bit of power out of. as you know detonation is the first thing thats going to destroy your engine. so detset was the first thing i chucked on the car, after any changes.

another thing that helps stop the amount of oil collected/throwen out is the actual size of the breather. bigger hole, less velocity, so will carry less oil out with it. had issues on the kp with the stock sized breather at hi rpm. welding on a 1" pipe in place of the stock 1/2"? fixed the problem

[QCADTA]

if you wanna run a catch can like my wee one (soon to be replaced) you can put a divider in the middle of oi and baffle it with something like steel gauze/ wool or something to work as a filter but not do tight that it impeads flow. just learning that ca18s nmore often than not need vacuum on the inlet side to reduce crankcase pressure as they are quite heavy breathers, the age of the engine probably doesnt help me either, ill be changing my setup to something more substantial in the near future.