Rocker cover hoses

[bigpaulo 239]

Ive seen croosflows with rocker covers on them that have a breather, always thought they looked pretty cool. But before I do that I need to figure out what the hoses do and if I currently have them in the right spot.

Years ago I changed the carby over to a holley with a 9inch air cleaner, I remember I had to reroute the hoses, but I cant remember why I did it or even if it's right. Anyway, the pcv valve in the oil cap goes around to a spot at the base of the carby, and also tees off on that line to the charcoal cannister with a valve/solenoid in it. The other one at the back of the rocker cover is just hanging loose. I never connected it to anything. Car runs fine but I just never ever bothered to check if id done this right...

Also, if I wanted to put one of those breathers on, where do I put it, and where do the hoses go then?

And what exactly does the charcoal cannister do? What happens if I dont have one? I swear ive seen motors without a pcv, or its going to a completely different place then the charcoal cannister...

Cheers!

[bear351c 10,271]

I honestly can't remember the hoses from my old X-flow, 'cos I threw it in the rubbish bin, when I stuck the Clevo in, but, in general terms..........

 

PCV - Pressure control valve - When oil/fuel are warmed up, they expand. This valve allows the pressure out. If you block all the outlets, your rocker cover will explode. (not really) So the car guys, put a hose to the base of the carby, to draw these gases out and reburn them. The carbon cannister collects fuel/oil vapour, allows it to condensate, and again, get reburnt. All part of the Emission standards game. Hoses should be oil resisitant type, otherwise they go all gooey and soft. 

Can use heater hose in a pinch, but, change it every year. 

 

If Mr Plod is clued up, he will notice the hoses missing and possibly give you a free trip to the nearest vehicle inspection centre. Do not pass GO, spend $200.

 

Will your car run better or worse without them, no. Will it make more pollution, yes. 

[bigpaulo 239]

Why do people put those breathers on the rocker covers? What do they replace?

[wagoon 2,429]

The rear hose is attached to the standard air cleaner assembly. It attaches underneath and vents inside the airfilter so it is sucked straight back into the engine through the top of the carby. As bear said its all to do with pollution and can be defected if not on your vehicle. But then again you can be defected for not having your windscreen washer bottle full in some states as well, no bullshit.

As you said filters look cool that's why people do it, Same reason they cut coil springs to drop a car. just as illegal as each other in the end.

[ando76 4,354]

Pcv gases are shit and introducing them back into the inlet manifold sucks arse as its full of yucky oil mist and vapours. Only air and fuel should go into the inlet in a performance application.
That's is why people piss them off. Is that legal? No.
Essentially the engine needs to be able to breath in and breath out. A filter on the rocker cover allows it to breath in and to a certain extent, breath out.
I'm not a fan of those breathers that screw into the rocker cover. Generally they leak oil and then that goes down onto the rocker cover and then onto the extractors and makes a mess.
If you are after a stealth look you could take the hoses down to a breather tank below the charcoal cannister.
Just make sure you have a big filter on the top of the tank.

[BigCav 464]

PCV stands for Positive Crankcase Ventilation

 

its a very basic system and no issue at all using a breather on the rocker cover

 

when an engine is running gasses and emmissions are created inside mostly from gas that escapes past the piston rings etc, in an old car these were just vented to the atmosphere by a hose and would drop oil mist and also release emmisions out to the air

 

now they vent that air back into the engine so it can be reburnt (better for the environment)

 

there is a suction hose and an inlet hose, the suction hose is routed from the inlet manifold under the carby (throttle body) so that it sees constant suction, this sucks the air contstantly into the engine through the pcv valve from out of the rocker cover, if they just left it at that the crankcase would depressureize but there wouldnt be any airflow to suck the air out, so they also add a vent on the rocker cover to let fresh air in, this hose goes from the rocker cover to the air cleaner assembly at a point past where the air would be filtered so only clean air is getting sucked into the engine cause you obviously dont want dirty air mixing with your oil

 

reading above people assume that its sucked into the top of the carby, that is incorrect, the pressure is lower bellow the carby then in the air cleaner so the air will always flow through the engine and out the pcv valve, most people, myself included remove this inlet hose when changing air cleaners and put a stand alone filter on the rocker cover, nothing changes in how it operates it just looks better

 

note too that v8's have the pcv and inlet on different rocker covers so it flows from one head through the crankcase and out the other head, better design then what they can do on a 6

[BigCav 464]

on a standard motor the pcv will only see a little bit of oil mist and cause no issues, on a worn out motor or high performance motor excessive amounts of oil mist can be fed back into the motor causing oil inlet manifolds and spark problems etc so thats when a catch can is fitted, these seperate the oil from the air before its fed back in to be burnt off

 

dont remove the pcv system

[BigCav 464]

a charcoal canister is similar to a pcv in the fact that its a system preventing emmisions venting to the atmostphere, it is hooked up to the fuel tank (which is now supposed to be a sealed system) so no fuel vapor escapes to the atmosphere, the vapour passes through the charcoal so no bad gasses escape etc, realistictly the carbon is good for about 80,000km and is supposed to be replaced but nobody does it lol, they will also vent back to the engine so vapours can be burnt off etc

[ando76 4,354]

Yes it enters into the bottom of the carb - through the pcv dick.  well aware of that. 

 

Is that puss good for an engine - no not really.  In worn engine excessive blow by can cause lots of misty oil to enter the inlet track.  What is the problem with this? Well oil can and does cause pre-ignition if it runs into the inlet.  It also takes up room where air/fuel is supposed to be. 

 

Most old engines had a 'walking cane' which simply dumped this puss onto the ground and into the atmosphere.  Is that good for the environment - No.  Is it good for the engine - Yes. 

 

Would I delete the pcv system on a standard road car motor used as a daily driver? No.

 

Would I do it on a hot street engine that sees only a couple of days a week running - Yep.  Is that legal - No. 

 

And as Big Cav has pointed out these systems are supposed to be serviced but no one does. 

 

If you are going to remove the pcv valve from the system - DO NOT block off the PCV dick on a Holley carb.  You will screw with the idle circuit.  instead run a hose out of hose up to the inside of the air cleaner with a pcv valve in there.  It will pull extra air into the base of the carb at high rpm and as most Holley's run rich up top it usually cleans them up. 

 

We do it to the meth race 350 Holley's as a way of getting extra 'metered' air into the inlet manifold - just another way of trying to get around the restriction that a 350 holley poses to these engines.

[wagoon 2,429]

Thank you for the explanation Cav, Clearly I was completely half wrong which is normal. Glad I could muddy the waters for a while

[BigCav 464]

" It also takes up room where air/fuel is supposed to be "

 

 

 

True, but also remembering that when you want the largest volume of useable air you are on full throttle, which means vacuum is also at a minimum and the flow through the pcv system is at its minimum volume when airflow into the engine is at its maximum so the pcv has negligable effects

[bigpaulo 239]

this has been very informative, thanks for all that cav. how does the solenoid work on T'eed hose of the pcv system? the one that runs down to the charcoal cannister? it has wires going off into the loom, is it somehow electronically controlled to allow vacuum into the cannister?

[bear351c 10,271]

PCV stands for Positive Crankcase Ventilation

 

Absolutely correct.....(fookin' work, still in my head). Thanks BigCav.