Pos. crankcase vent.
Thread Starter
Drifting
Joined: Oct 2001
Posts: 1,550
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From: Richmond VA
Pos. crankcase vent.
My 62 has a 300hp 327 it had a breather cap on the oil filler tube and a tube off the back of the intake manafold extending down the rear of the engine. Is this close to correct? What am I missing? Will the way it's set up work ok or will I have problems with it like possible damage to the engine.
Race Director
Joined: May 2000
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Only '61 and '62 models sold in CA had positive crankcase ventilation; 49 state models still had the breather cap and road draft tube.
PCV systems were required for all cars sold in the US beginning in 1963. The only car engine Chevrolet ever built without PCV after 1962 was the '67 L-88, which had a road draft tube, and for that reason it was illegal to register for public road use.
If your carburetor has a port for a PCV system you would actually be doing the engine a favor by implementing a PCV system since it postively purges blowby from the crankcase, which will reduce oil dilution and sludge formation.
Duke
PCV systems were required for all cars sold in the US beginning in 1963. The only car engine Chevrolet ever built without PCV after 1962 was the '67 L-88, which had a road draft tube, and for that reason it was illegal to register for public road use.
If your carburetor has a port for a PCV system you would actually be doing the engine a favor by implementing a PCV system since it postively purges blowby from the crankcase, which will reduce oil dilution and sludge formation.
Duke
Last edited by SWCDuke; Apr 13, 2005 at 11:50 PM.
Melting Slicks
Joined: Jul 2000
Posts: 2,097
Likes: 99
From: Boston MA
Sounds like your car is correct. If the system is working as designed, fresh air comes in through the mesh on the cap of the oil fill tube; travels through the crankcase; and, exits out the road draft tube at the back of the block, taking all the blow-by and oil mist with it. The road draft tube exits at the back of the motor, down by the transmission. The transmission tunnel area should, by now, be covered with oil and dirt. That's smelly, and it looks like hell, but who sees down there anyway, and it protects the area well. After you clean it up, it'll be nicely preserved.
If it were my car, I'd install the RPO PCV system. Who's to know your car didn't come from California? Much better for the engine; cuts down on the smell; and, keeps the bottom of the car clean.
If it were my car, I'd install the RPO PCV system. Who's to know your car didn't come from California? Much better for the engine; cuts down on the smell; and, keeps the bottom of the car clean.
Intermediate
Joined: Aug 2003
Posts: 30
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From: Rogers AR
You all have me thinking?
I have a 62 with a 68' 350 that has an edelbrock manifold manifold with an oil filler and breather cap and non vented valve covers ... to my knowledge there isn't another vent on the engine. Should there be one? If so where would I vent it from? I haven't driven it too much since installing this setup, so if I created a problem, haven't seen it yet. Appreciate any help.
Melting Slicks
Joined: Jul 2000
Posts: 2,097
Likes: 99
From: Boston MA
Yes, you need another vent. Fresh air needs to go in, and then the contaminated air needs to come out. When it comes out, it can go to the atmosphere as in the old road draft tube systems. Or, it can go to the carburetor to be recycled as in a modern PCV system.
If your '68 block doesn't have the second hole in the block behind the distributor, then do what Chevrolet did in 1968. Use the valve covers. Get '68 valve covers with vents in them. Get the nice ribbed aluminum ones. That's what I use. Plumb the PCV system just like Chevy did when the block was used.
1. Hose from a vacuum source, through a PCV valve to one valve cover.
2. Hose from the other valve cover to the base of the air filter.
If your '68 block doesn't have the second hole in the block behind the distributor, then do what Chevrolet did in 1968. Use the valve covers. Get '68 valve covers with vents in them. Get the nice ribbed aluminum ones. That's what I use. Plumb the PCV system just like Chevy did when the block was used.
1. Hose from a vacuum source, through a PCV valve to one valve cover.
2. Hose from the other valve cover to the base of the air filter.
Burning Brakes
Joined: Oct 2004
Posts: 840
Likes: 12
From: Ventura County CA
All this talk has me a bit confused. 
My 58 has a basic 283 engine.
Currently I have the oil fill tube in the manifold with the breather cap on it- I have sealed finned valve covers and the tube exiting from the back of the manifold down toward the tranny.
I have recently installed an edelbrock performer carb.
Should I remove the tube in the back and run a line from that spot on the manifold into a pcv valve and then to the carb?
I am so confused.
Does someone make a conversion kit?
Any suggestions would be appreciated. Thanks
My 58 has a basic 283 engine.
Currently I have the oil fill tube in the manifold with the breather cap on it- I have sealed finned valve covers and the tube exiting from the back of the manifold down toward the tranny.
I have recently installed an edelbrock performer carb.
Should I remove the tube in the back and run a line from that spot on the manifold into a pcv valve and then to the carb?
I am so confused.
Does someone make a conversion kit?
Any suggestions would be appreciated. Thanks
Team Owner
Joined: Oct 2000
Posts: 38,897
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From: Washington Michigan
Your car is equipped as it came from the factory; you can leave it as is with the road draft tube, or convert it to a "closed" system by adding the '62 adapter elbow, hose, and PCV valve to the carburetor. Paragon has the adapter elbow that replaces the road draft tube elbow, hoses, and PCV valve if you want to do that. The adapter elbow is about $60, and the rest of the setup is about $40.
It will work fine if you leave it just as it is now.
It will work fine if you leave it just as it is now.
Race Director
Joined: May 2000
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You can either leave is as is or convert to PCV. PCV is more effective at removing blowby from the crankcase and this will reduce oil dilution and sludging.
PCV will also improve fuel economy since blowby is primarily unburned air-fuel mixture, which PCV captures for consumption by combustion rather than releasing to the atmosphere.
Anyone with a pre-'68 block can easily implement a workable PCV system using a breaker oil fill cap and either the '62 or '63 California outlet routing and valve as long as the carb has a provision for PCV entry, which most do.
Duke
PCV will also improve fuel economy since blowby is primarily unburned air-fuel mixture, which PCV captures for consumption by combustion rather than releasing to the atmosphere.
Anyone with a pre-'68 block can easily implement a workable PCV system using a breaker oil fill cap and either the '62 or '63 California outlet routing and valve as long as the carb has a provision for PCV entry, which most do.
Duke
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Intermediate
Joined: Aug 2003
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From: Rogers AR
One more "dumb" question
From my earlier post I have a 350 with an aluminum edelbrock intake and the engine only vents from the oil filler breather cap... . It has solid valve covers that are too new and too nice to cut into, so venting that way is not an option. The block doesn't have a port on the back of it either. So venting there isn't an option either.
After getting home yesterday I noticed the aluminum intake has a threaded plug about 3 inches behind the carburetor. I took the plug off and it did not smell like gasIs this threaded plug a potential vent for the crankcase? The carburetor is also an edelbrock with a fairly large plugged port off the back of it, is it possible to vent the manifold into the back of the carburetor? The two front vents pull vacuum, not sure what the large back vent does?
Obviously, I am showing my lack of knowledge but if I knew I wouldn't be asking and exposing my lack of knowledge, but as always the help and info I get from this forum is invaluable and very much appreciated.
After getting home yesterday I noticed the aluminum intake has a threaded plug about 3 inches behind the carburetor. I took the plug off and it did not smell like gasIs this threaded plug a potential vent for the crankcase? The carburetor is also an edelbrock with a fairly large plugged port off the back of it, is it possible to vent the manifold into the back of the carburetor? The two front vents pull vacuum, not sure what the large back vent does?
Obviously, I am showing my lack of knowledge but if I knew I wouldn't be asking and exposing my lack of knowledge, but as always the help and info I get from this forum is invaluable and very much appreciated.
Melting Slicks
Joined: Jul 2000
Posts: 2,097
Likes: 99
From: Boston MA
You can't use a 350 with the C1 and C2 ribbed aluminum valve covers. Those valve covers don't have vent holes in them for a PCV system. Some people have cut holes in them to do this. But it sounds like you don't want to.
Right now you have no PCV system. The vent is the oil fill cap. All the crankcase fumes spew out of there. May not be too much if your engine is new. Your engine compartment may get covered in oil mist with sustained operation at higher rpms. Like a trip on a highway for over 20 minutes. Your oil won't last long. But that might not be a problem if you don't drive the car much and change it often.
You can solve this by using 350 valve covers. Chevy made nice aluminum ribbed ones for this engine.
Right now you have no PCV system. The vent is the oil fill cap. All the crankcase fumes spew out of there. May not be too much if your engine is new. Your engine compartment may get covered in oil mist with sustained operation at higher rpms. Like a trip on a highway for over 20 minutes. Your oil won't last long. But that might not be a problem if you don't drive the car much and change it often.
You can solve this by using 350 valve covers. Chevy made nice aluminum ribbed ones for this engine.
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I have a "home made" road draft tube installed in the rear of the lifter valley of the SB400 in my 56. I have installed one of the check valves (like used on dragster headers) in the right exhaust pipe. My road draft tube is connected to this check valve which subsequently sucks all vapors from the crank case-----------------------------WITHOUT THEM FIRST HAVING TO GO THROUGH THE INTAKE SYSTEM (Rochester FI).
Last edited by DZAUTO; Apr 17, 2005 at 10:18 AM.
Team Owner
Joined: Oct 2000
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From: Washington Michigan
Originally Posted by red62
After getting home yesterday I noticed the aluminum intake has a threaded plug about 3 inches behind the carburetor. I took the plug off and it did not smell like gasIs this threaded plug a potential vent for the crankcase? The carburetor is also an edelbrock with a fairly large plugged port off the back of it, is it possible to vent the manifold into the back of the carburetor? The two front vents pull vacuum, not sure what the large back vent does?.
With a late no-hole block, you have to use a hole in at least one of the valve covers for the other end of the PCV system, in combination with the oil fill tube cap. You can either use the vented oil fill tube cap as the intake side and a PCV valve in the valve cover with a hose to the rear of the carb as the exhaust side, or you can use a breather in the valve cover as the intake point and a '66-'67 oil fill tube with a sealed cap and PCV valve in the tube with a hose to the back of the carb as the exhaust side.
If all you have is the vented cap on the oil fill tube, you have no crankcase ventilation, only pressure relief, and it'll blow hot oil mist out of the cap all the time, especially at high rpm.
Burning Brakes
Joined: Nov 2001
Posts: 1,179
Likes: 312
From: St. Petersburg FL
Here is an older thread on the topic. See the posts by Curtis--he posted some pics showing how he machined his Edelbrock manifold to accept a PCV valve. Note, he also put a spash shield on the underside.
http://forums.corvetteforum.com/show...um_id=4&arch=1
http://forums.corvetteforum.com/show...um_id=4&arch=1
Burning Brakes
Joined: Nov 2001
Posts: 1,179
Likes: 312
From: St. Petersburg FL
Originally Posted by JohnZ
Thanks, David - I've been trying to locate that old thread to get the photos as references for months, and couldn't find it; he had a slick solution.
Intermediate
Joined: Aug 2003
Posts: 30
Likes: 0
From: Rogers AR
Thanks to everyone for their valued input... I guess I will just have to decide what to do ..."tastefully alter the valve covers" or go to another style valve cover.
I epecially appreciate the info on the necessary intake of crankcase gases and the venting of them. I assume that if I were to alter the valve covers such that gas was pulled from the valve cover to the base of the air cleaner, that would be ok for pulling the crankcase vapors in the filler tube and out the valve cover pcv vent to the air cleaner base? If I stay with these valve covers, this seems the best route to go.
As the engine is now , only the filler tube acts as a vent, could there be so much pressure in the crankcase that it would help force oil out, since I do have a nagging leak that I assumed was from the oil pan?
I have only driven about 10 miles or so, since putting the car back together, so likely I haven't hurt anything.
Again, you guys just don't know how valuable your information is and how much I appreciate it.
I epecially appreciate the info on the necessary intake of crankcase gases and the venting of them. I assume that if I were to alter the valve covers such that gas was pulled from the valve cover to the base of the air cleaner, that would be ok for pulling the crankcase vapors in the filler tube and out the valve cover pcv vent to the air cleaner base? If I stay with these valve covers, this seems the best route to go.
As the engine is now , only the filler tube acts as a vent, could there be so much pressure in the crankcase that it would help force oil out, since I do have a nagging leak that I assumed was from the oil pan?
I have only driven about 10 miles or so, since putting the car back together, so likely I haven't hurt anything.
Again, you guys just don't know how valuable your information is and how much I appreciate it.
Burning Brakes
Joined: Oct 2004
Posts: 840
Likes: 12
From: Ventura County CA
Besides case configuration are the PCV valves the same?
Are they flow rated or is there anything that would need to be determined in selecting the valve itself to use in the conversion from draft tube?
Thanks
Are they flow rated or is there anything that would need to be determined in selecting the valve itself to use in the conversion from draft tube?
Thanks
Race Director
Joined: May 2000
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PCV valves are available in a varienty of physical configurations and flow characteristics, I've never seen any flow-depression specs, but I've tested a few.
If you select any valve that was used for SB applications you will probably be in the ballpark. Most years all SBs regardless of power rating, used the same PCV valves and sometimes BBs used the same valves as SBs.
Duke
If you select any valve that was used for SB applications you will probably be in the ballpark. Most years all SBs regardless of power rating, used the same PCV valves and sometimes BBs used the same valves as SBs.
Duke
Last edited by SWCDuke; Apr 18, 2005 at 03:15 PM.
