bonkas

Rules for PCV/Rocker Cover Vents

Recommended Posts

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

Share this post


Link to post
Share on other sites

Not sure on rules, but both of my running 4g63s have the hoses running to a baffled catch can

  • Like 1

Share this post


Link to post
Share on other sites

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.

  • Like 4

Share this post


Link to post
Share on other sites

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.

  • Like 3

Share this post


Link to post
Share on other sites

Share this post


Link to post
Share on other sites
9 hours ago, Roman said:

... having a stinky fumey car. Wears thin pretty quick.

To each their own ... some like it hot, stinky, loud and fast.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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

  • Like 1

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

if you're worried about sucking oil back into the combustion process, put an air/water/oil separator off a compressor between the pcv and the intake manifold to collect excess fluids....it will also indicate the health of your engine at a glance

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now