Valve Cover Breather Question....

[engine24355]

Have a question regarding how many breathers should be on a SBC 350. I have the same valve covers as pictured in Tfeverfred's thread below:

http://www.tbucketeers.com/forum/tfeverfreds-project-t437/index26.html

I noticed when I first got my T that there were two breathers when I always thought there should be one due to the size and mildness of my 350 (dual carb, but nothing radical). Also, from the picture posted by LumenAl, looks like the coves have two breathers as well. Any thoguths on why there are two as opposed to one? Is there something special about these retro style covers? Thanks!!!

 

[Yogi]

Most I've ever seen was 1 breather and 1 PVC. I think you need a negative pressure on the crankcase. Just my 2 cents worth....heh heh

 

[Lee_in_KC]

What you want is "positive crankscase ventilation," whereby the nasty combustion by-products are evacuated from inside your motor. Just venting the valve covers will not create positive ventilation. You need a breather on one side and a PCV valve on the other, hooked up to a vacuum source through a tube. Depending on which carb you are using, there may be a dedicated port (with a 1/4" hose nipple) on the base of the carb. Depending on which manifold you have, there may be a tapped hole below the carb where you can hook up a tube. DO NOT use the tap at the back of the manifold on the runner to #8 cylinder. This will cause that cylinder to run lean or oil-choke the sparkplug.

Hope this helps!

Happy hot-rodding!

 

[old round fart]

If you have a pcv valve you don't need (or want) an additional breather. Remember the pre pcv motors had the tube that ran from the back of the motor behind the distributer down the passenger side of the motor. The breather/oil fill port was on the front of the intake. Using real early valve covers takes planning. Without some vent, you WILL have oil leaks.

 

[engine24355]

I do have a PCV valve with a vacume hose conected to the front Edelbrock carb at the bottom (dual carbs). I understood the same thing as far as having the breather on the opposite side as the PCV valve. Basically, I have a PCV valve and breather on the passanger side of the engine and a breather only on the driver side of the engine (sitting in the car). Sounds like I need to do something with the breather on the passanger side. How do I resolve this and how much damage can this do? Do not want to damage the engine any further. Thanks!!

 

[Baby Huey]

The whole idea here like the guys have said ,is to get a "Flow-Thru" ventilation of the block. In otherwords, you want the fresh air to enter thru the valve cover, down thru the crankcase and intake valley and then be purged out thru the PCV valve and cycled thru the intake system into the combustion chamers and hopefully burned and passed thru the exhaust....
NOW, IFFFFF you have a camshaft that is not producing enough Vacuum to operate the PCV valve at the correct time, you may experience what seems like a Vacuum Leak. If you are experiencing rough idle and backfire or lean out, then you should swap different PCV valves untill you find one that will operate correctly on your engine.... "BH"
http://en.wikipedia.org/wiki/PCV_valve

 

[LumenAl]

When I had these covers on my car

I had breathers only because the block is vented behind the distributor (where PCV valve is) and I plumbed it to my carb.

 

[engine24355]

The whole idea here like the guys have said ,is to get a "Flow-Thru" ventilation of the block. In otherwords, you want the fresh air to enter thru the valve cover, down thru the crankcase and intake valley and then be purged out thru the PCV valve and cycled thru the intake system into the combustion chamers and hopefully burned and passed thru the exhaust....
NOW, IFFFFF you have a camshaft that is not producing enough Vacuum to operate the PCV valve at the correct time, you may experience what seems like a Vacuum Leak. If you are experiencing rough idle and backfire or lean out, then you should swap different PCV valves untill you find one that will operate correctly on your engine.... "BH"
http://en.wikipedia.org/wiki/PCV_valve

Thanks for the information BH. So your suggestion is to try a different PCV valve and leave the two breathers. Would it be possible to plug the breather on the passanger side?

 

[Baby Huey]

YES.....Go ahead and plug one side.

Yes ,you could plug one side. As long as you have some way to get clean air into the block. Engines create a pressure when the crank and rods/pistons are rotating, if you don't have a way to bleed that pressure you will have more oil leaks and blown crank seals than ya know what to do with..
Thats why in the old days (and today too) we use the breathers on the valve covers, throw away the PCV valves and all the hoses.
You may find that getting a good idle with Dual Carbs and a cam is going to be hard to do with a PCV system. Finding a parts guy that knows what he's doin to find you a PCV that will work, may be hard to do. The PCV's have different vacuum ratings, kinda like Holley Power Valves.. You may have to get on line or find a AC Delco or other catalog and search til you find the values of their PCV 's..Match that with your Vacuum readings...
Jus my 2 bits "BH"

 

[engine24355]

Right now my idle is not too bad (once she warms up), but want to make sure the engine is set up right. Therefore, how should I plug the passanger side breather?

 

[Baby Huey]

You can buy rubber plugs at any auto parts store..."BH"

 

[engine24355]

I looked a little closer at my breather set up and noticed a few things.

1. PCV valve (passanger side) with hose running to front carb (closest to radiator).
2. Vacume hose running to distributor from back carb (closest to firewall).
3. Hose running from back carb (same location as PCV connection on front carb) down behind engine block.
4. Valve cover breather on both sides.

I hope to look into more closely tonight, but I wanted to pass this along and see what the experts think. Again, my engine seems to run good and strong, but trying to avoid any problems. Thanks!!

 

[Baby Huey]

I looked a little closer at my breather set up and noticed a few things.

1. PCV valve (passanger side) with hose running to front carb (closest to radiator).
2. Vacume hose running to distributor from back carb (closest to firewall).
3. Hose running from back carb (same location as PCV connection on front carb) down behind engine block.
4. Valve cover breather on both sides.

I hope to look into more closely tonight, but I wanted to pass this along and see what the experts think. Again, my engine seems to run good and strong, but trying to avoid any problems. Thanks!!

I dout if we are all experts here, for sure I'm not one of em !! LOL.....

Item #3: That hose running down behind the block.....Probably goes to to the Vacuum Modulator on the trans. You are running a TH-350 or ????
The previous owner had this set up running ok ? No poping or lean out when it runs or when ya jump on the throttle ? Smooth and no lean surging at cruise?
If so then I would leave well enough alone, don't fix if it isn't broke.....yet. "BH"

 

[engine24355]

I dout if we are all experts here, for sure I'm not one of em !! LOL.....

Item #3: That hose running down behind the block.....Probably goes to to the Vacuum Modulator on the trans. You are running a TH-350 or ????
The previous owner had this set up running ok ? No poping or lean out when it runs or when ya jump on the throttle ? Smooth and no lean surging at cruise?
If so then I would leave well enough alone, don't fix if it isn't broke.....yet. "BH"

I am running a TH-350 and the first thing I thought was that hose must go down to the tranny, but just have not had time to look closer yet.

Honesly, I do not jump on it very much because I have not driven the car much yet (changing things up). The times I have jumped on it some, the only thing I noticed was a little oil spraying out of the driver side breather (not much). Have not noticed it running lean, but again still working and learning about how the engine was built as I did not build myself or have built.

My thought was to leave alone for now, but as you stated the "yet" is what is worrying me. Would like to fix now to avoid any future problems.

Thanks!!

 

[VegasBruce]

What I did on mine was use the oil filler tube in the front of the manifold. Then punch a hole in the back of the manifold under the coil for the PCV valve. Sorry for the blurry pic.

 

[engine24355]

Thanks for all the advice guys. I think I am just going to get a plug the passanger side breather. Will see what that does and go from there. Plugging seems to be the easiest thing to do. Thanks!!

 

[engine24355]

Well I feel like an idiot now. Worked on my T this weekend and one thing on the list was to plug the passanger side breather. Took to the parts store and as I was talking to one of the guys, realized, there should be an oil cap on the passanger side instead of a breather. Man, I pulled a major brain fart on this one. I was so concerned with getting the proper vacume that I totally over looked that all I needed to do is replace the breather with an oil cap...DUH. Anyway, picked up a retro style oil cap and we are good to go now.