valve cover breathers into new air cleaner

timmurphy · Feb 28, 2011

I installed new chrome valve covers on my '71 coupe 302 2 barrell, along with a free flow chrome air cleaner My question is; what do I do with the breather hoses from the valve covers that use to go into the air cleaner ? Are ther caps that go onto the valve covers to cap off these hose ports?

72fastback · Feb 28, 2011

I installed new chrome valve covers on my '71 coupe 302 2 barrell, along with a free flow chrome air cleaner My question is; what do I do with the breather hoses from the valve covers that use to go into the air cleaner ? Are ther caps that go onto the valve covers to cap off these hose ports?

if you look at the pic of my engine you can get these kind of breather caps for your valve covers. I have one on each side.

TommyK · Mar 1, 2011

I installed new chrome valve covers on my '71 coupe 302 2 barrell, along with a free flow chrome air cleaner My question is; what do I do with the breather hoses from the valve covers that use to go into the air cleaner ? Are ther caps that go onto the valve covers to cap off these hose ports?

Many but not all air cleaner bases have a knock out where a barbed fitting can be installed to accept the valve cover breather hose. I highly recommend you keep the pcv system fully functional which includes connecting the valve cover breather to the air cleaner although many people run a pcv valve on one cover with just a breather cap on the other with no issues.

72fastback · Mar 1, 2011

I installed new chrome valve covers on my '71 coupe 302 2 barrell, along with a free flow chrome air cleaner My question is; what do I do with the breather hoses from the valve covers that use to go into the air cleaner ? Are ther caps that go onto the valve covers to cap off these hose ports?

Click to expand...

Many but not all air cleaner bases have a knock out where a barbed fitting can be installed to accept the valve cover breather hose. I highly recommend you keep the pcv system fully functional which includes connecting the valve cover breather to the air cleaner although many people run a pcv valve on one cover with just a breather cap on the other with no issues.

Is there a good reason apart from legal issues to keep the Pcv valve hooked to the air cleaner.

thundertc64 · Mar 1, 2011

The PCV is an emissions device that allows the pressure and corrosive gasses in the crankcase to vent, without venting these harmful gasses to the environment. The directional valve is in place to prevent a backfire from spreading to the crankcase. In the event of a backfire into the intake manifold, the PCV is supposed to seal shut, preventing the flame front from traveling into the crankcase. Without this directional valve in place (and fully functional) a backfire could also cause a crankcase explosion.

All motors will experience some degree of Blowby. Even a freshly rebuilt motor can experience between 5-10% Blowby, as checked with a Leakdown test. (Blowby is not the only source of crankcase pressure however. Due to the reciprocation of the pistons there will be a build up of pressure due to the air not being able to flow as fast as the pistons are moving in the higher RPMs) Blowby of combustion gasses introduces fuel and other combustion by products into the crankcase. Raw fuel, moisture, and various acidic materials will all contaminate the engine oil. Moisture can also enter the crankcase due to condensation overnight.

The good news is that most of these contaminants are highly volatile, meaning they will vaporize at relatively low temps; around 200F. Once these contaminants and moisture have volatized though, they must be purged from the crankcase. This is where a crankcase ventilation system comes in.

TommyK · Mar 1, 2011

I installed new chrome valve covers on my '71 coupe 302 2 barrell, along with a free flow chrome air cleaner My question is; what do I do with the breather hoses from the valve covers that use to go into the air cleaner ? Are ther caps that go onto the valve covers to cap off these hose ports?

Click to expand...

Many but not all air cleaner bases have a knock out where a barbed fitting can be installed to accept the valve cover breather hose. I highly recommend you keep the pcv system fully functional which includes connecting the valve cover breather to the air cleaner although many people run a pcv valve on one cover with just a breather cap on the other with no issues.

Click to expand...

Is there a good reason apart from legal issues to keep the Pcv valve hooked to the air cleaner.

Yes. The pcv system mitigates the potential for excessive crankcase pressure common in older or higher mileage vehicles which can cause oil leaks, piston ring blowby and even cause your dipstick to pop out under hard acceleration.

73vertproject · Mar 1, 2011

:goodpost:

Thanks for the great information, guys. I thought all that stuff was just to keep the EPA guys happy on the design end. Now I know it has a real world purpose as well.

Doc

72fastback · Mar 1, 2011

So what you are saying is that the breather caps you see in my pic are not enough the pcv valve would be better?

thundertc64 · Mar 1, 2011

So what you are saying is that the breather caps you see in my pic are not enough the pcv valve would be better?

pcv would help pull pressure and contaminants out quicker

FastE · Mar 1, 2011

So what you are saying is that the breather caps you see in my pic are not enough the pcv valve would be better?

I may have missed some one saying this if I did forgive me.

The PCV valve should be plumbed to the intake vacum port not the air cleaner.The PCV valve replaced the old down draft tube on older engines.This system burns the gasses that are created in the crank case.You WANT to have a vacum / circulation on the crank case.

If you look at the factory system and think about how it works it will help you to understand what is going on..

The factory system has the pcv located on one side of the engine it is plummed to the intake vacum port,thus creating suction.The check ball in the valve is pulled off of it's seat.This pulls the gasses from the crank case to be recycled through the fuel being burnt.In a good engine very little blow by etc...does not hurt your performance at all.

Well now that we are pulling on the crank case the flow has to come from some where.

On the opposite valve cover you will have a vent that on our cars goes back to the air cleaner and has a smaller air filter to allow filtered air to flow through the crank case.This give you your circulation.Fresh air in bad air out.

If you want to run an open air cleaner you can use a vented oil cap such as the one on Roys engine to filter the in comming air on one side.

It is a proven fact that race engines like crank case vacum,helps with ring seal.You will usually see two types of systems on race engines.

The first being the valve covers vented to the header collectors using divertor or one way valves.

The best system is the one using a driven vacum pump that is plumbed to the valve covers.

My hope is that I have not confused any one.I am a beleiver in the PCV valve.It will keep you from getting oil leaks and oil pooling up on your valave covers intake etc....

1971mach1 · Mar 2, 2011

So what you are saying is that the breather caps you see in my pic are not enough the pcv valve would be better?

With 2 breather caps like you have, you are just venting the bad crankcases gasses under you hood. These can easily get into the passenger compartment too.

With a PCV (on the pass side valve cover connected to intake vacuum), the bad gasses get sucked into and burned by the engine. The breather on the driver side valve cover just lets clean air into the crancase to replace the bad air pulled out. It works fine with a filtered breather like you have on the driver side (as long as it's not clogged with oil).

The pipe that goes to the air cleaner on factory stock breathers is just a refinement that makes it a closed system. It pulles clean air from the air cleaner. This has the benefit that incase there is not enough vacuum on the PCV side to pull out the gasses, they just go back out the breather and into the air cleaner to be burned (instead of directly into the atmosphere). The closed system is not necessary if you make sure the breather filter is clean and replaced if clogged.

72fastback · Mar 2, 2011

Thanks a lot for the reply's guys. I learned something I had no idea about. I thought it was just emissions control. I will get a pcv for the car for sure now. Can I get that from the sponsors?

Mustang72ht · Mar 15, 2011

If i have to much oil coming out of my pcv valve, do i have engine problems?

FastE · Mar 16, 2011

If i have to much oil coming out of my pcv valve, do i have engine problems?

Maybe or maybe not.What valve covers are you running? If you do not have an oil baffell under the PCV or filler cap you will get oil . If you have baffells in you may have valve seals / guide wear etc...

72HCODE · Mar 16, 2011

As a person that started with no PCV system, i HIGHLY recommend having one.

even an engine in good shape can leak lots of oil out the breathers.

Baffles in the valve covers help a lot but you will always end up with oil cleanup on top of the engine when using Breathers, even filtered ones.

you can expect a few tea spoons of oil sitting on the valve cover tops after a day of driving, even if the engine is in good shape.

when my engine was rebuilt 3 years ago i used breathers even with baffles and new valve covers and new breathers with carbon filters inside them i would routinely have to take a rag and wipe down the tops of the valve covers.

now when my engine was worn out before rebuild there was even more oil coming out of the breathers.

additionally before installing a PCV system i had oil leaking from:

the rear seal

the front seal

Fuel pump

oil filter

a oil gallery plug.

by restoring the pcv on my engine i reduced the oil leaks to a little dribble here and there.

sm3570 · Mar 16, 2011

This is really good info. It should be wiki'd.

BigPinoyHunk · Mar 16, 2011

So what you are saying is that the breather caps you see in my pic are not enough the pcv valve would be better?

Click to expand...

I may have missed some one saying this if I did forgive me.

The PCV valve should be plumbed to the intake vacum port not the air cleaner.The PCV valve replaced the old down draft tube on older engines.This system burns the gasses that are created in the crank case.You WANT to have a vacum / circulation on the crank case.

If you look at the factory system and think about how it works it will help you to understand what is going on..

The factory system has the pcv located on one side of the engine it is plummed to the intake vacum port,thus creating suction.The check ball in the valve is pulled off of it's seat.This pulls the gasses from the crank case to be recycled through the fuel being burnt.In a good engine very little blow by etc...does not hurt your performance at all.

Well now that we are pulling on the crank case the flow has to come from some where.

On the opposite valve cover you will have a vent that on our cars goes back to the air cleaner and has a smaller air filter to allow filtered air to flow through the crank case.This give you your circulation.Fresh air in bad air out.

If you want to run an open air cleaner you can use a vented oil cap such as the one on Roys engine to filter the in comming air on one side.

It is a proven fact that race engines like crank case vacum,helps with ring seal.You will usually see two types of systems on race engines.

The first being the valve covers vented to the header collectors using divertor or one way valves.

The best system is the one using a driven vacum pump that is plumbed to the valve covers.

My hope is that I have not confused any one.I am a beleiver in the PCV valve.It will keep you from getting oil leaks and oil pooling up on your valave covers intake etc....

i'm glad this post came up!!! i am about to push STOCK 460 valve covers back on my motor and i looked at my dad's BOSS 351 to find out where the heck the two things go to. one is going into the intake for vacuum, and the other one is going into the air cleaner housing.

i replaced my stockish valve covers at the time when i had PROCOMP rockers and they were EVER SO SLIGHTLY touching the valve covers when running. i replaced them with some MOROSO valve covers with 2 breathers on each side. these valve covers are so thin they cracked on me and have zero baffles. i had to over silicone an area to make it stop leaking and it starting to leak some now again. so i'm ditching these cheapy moroso valve covers now.

one side has a large twist area where would obviously filtered breath cap on it and then that has a hole on top of that.

on the other side i have something that goes straight thru and it requires a big hose and is as big as a heater hose. i'm assuming this will go int othe air cleaner.

Mustang72ht · Mar 17, 2011

If i have to much oil coming out of my pcv valve, do i have engine problems?

Click to expand...

Maybe or maybe not.What valve covers are you running? If you do not have an oil baffell under the PCV or filler cap you will get oil . If you have baffells in you may have valve seals / guide wear etc...

Thanks for the answer, i´m using Holley valve cover, with no baffell.

72HCODE · Mar 17, 2011

i use the Polished Finned Aluminum covers, the aluminum is thick it has baffles and 2 twist on caps.

they are copies of the 351 boss covers. they make the same ones that said 351 cleveland on them.

i wanted these

because of the blank space in the center of the covers.

I bought a set of ignition wire holders from e-bay basically machined L brackets, that i tapped into the covers

then used the OEM ignition wire holders

so that the ignition wires had something holding them in place just like on the stock valve covers.

I then restored a OEM oil cap with the PCV hole replaced the seal and ran a line into my edelbrock intake on the driver's side.

on the passenger side i was able to use all the OEM piping and hook up directly to my OEM air cleaner like factory.

this restored the PCV system on my car.

valve cover breathers into new air cleaner

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