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Rules for PCV/Rocker Cover Vents


bonkas

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I seem to remember a thread on here a long time ago which I can no longer find discussing the rules on venting crankcase emissions.

I have gone to dual sidedraft carbs and wondering if I can simply block off the front PCV valve and put a filter on the rear rocker cover vent?

The engine is newly built from the ground up so I am hoping for very minimal blowby etc.

This is in an early 4g63:

PCV bottom left, plain rocker cover vent right hand side center (rear center of rocker cover)

image.png.d23de7618da7cdbd9e15318b2efb8038.png

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cert rules- when its an engine swap, emissions standard applies, and a post 75 engine needs an operational pcv system.

 

it seems to be one of those things that people think makes a big difference to performance- but having had engines both ways, I would always run a pcv system, it reduces the amount of stinky fumes.

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Part of what's good about having a PCV system with 2 lines is that it works two different ways. 

When you are at full throttle, it blows the crank case fumes out into the line without the PCV valve ahead of the intake.
Which then gets sucked back into the intake and combusted.

Then when you are at low throttle the PCV valve sucks fumes into the intake with the intake vacuum, which then pulls fresh air the other way through the crank case via the 2nd hose so you are getting active circulation. (assuming it's drawing more air through the valve than your pistons blowby... ha)

If you just dump both lines into a catch can then the only air that circulates through your crank case is combustion gas leaking past piston rings.

How much difference this makes in the short term is probably sweet F all. Maybe just need more regular oil changes or something. Dont know.
But its worth considering why there are two lines there in the first place before removing them. 

As Cletus has mentioned though, dont underestimate how much it sucks having a stinky fumey car. Wears thin pretty quick.

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So in regards to cert - I can just plumb them both into the air filter and be done with it?

The catch cans I see for sale have a filter on top and a catch can to catch any fluids but Im not sure how this is any different to putting a filter on the breather on the rocker cover?

Something like this im talking about: https://www.trademe.co.nz/motors/car-parts-accessories/performance/turbos/listing-1965388838.htm?rsqid=1121f181243042b59e10c83a27c359b3

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Alot of those ones are not baffled/the filter directly above where the breather ports go in. I got one with a removable top and fitted a plate just under the vent and steel wool inside to 'catch' the oil vapour, intake stays clean even on my tired old motor

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The turbo Mitsis have a very good system that drains back to sump, could just use that stuff and drain it to a catch can. With side drafts you'll want them perfect, any over fuelling or too rich and you may get bore wash or fuel vapours in the crankcase unable to escape.

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Im not too worried tbh but I am not sure if my modifications will require certification, if it does I will need to put in a catch can by the sound of it.

For the time being I will just add a smal filter to the breather pipe while I get the engine running.

You guys are a huuge help.

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  • 3 weeks later...

the hunter needs to have the rocker breather plumbed to the intake when ive made a filter set up.

its currently just venting next to the firewall, its manky as on a long drive.. even with windows down your still getting fumigated.

its not huffing like a 202 but its enough to be a pain

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Even at ~6k rpm I dont feel even the slightest bit of blowby out the breather hose, after two weeks of just having a hose hanging off the breather there isnt even any residue on the hose.

The engine is brand new though so Im not sure if this will slowly get worse or how long it will take to worsen.

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With Hunters I get an old radiator cap (which is the same as the oil cap) gut it an fit an pcv valve into that and connect to manifold, they idle and run better with the bonus of stopping or slowing their oil leaks.  

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