PCV

[D35 Torpedo]

I installed a pcv yesterday to solve an issue, but I've created another. First issue was fumes coming in from the road draft. I believe I had some fumes coming in from the road draft, but it also could have been from having half an exhaust. I put a tail pipe on and made a pcv. Solved any smells I was getting. But now, i've created a vacuum leak and the car has a hesitation. I'm sure completing the exhaust system could change the air/fuel as well. I like the pcv and always intended on making one to keep the oil cleaner, longer. So now i need to tune it around the new parameters. Has anyone else installed a pcv, and then had to retune the engine? 

[Sniper]

Well, the PCV is a metered vacuum leak so retuning isn't unexpected.

[kencombs]

6 minutes ago, Sniper said:

Well, the PCV is a metered vacuum leak so retuning isn't unexpected.

Absolutely correct.   Usually richening the idle mixture and maybe setting the accelerator pump in the richest hole will get it done.  .Some may need the path for off idle transition changed too.  Then there are different pcv valves that pass more or less air, or have a different rate of change from  idle to cruise.

I've chosen an early Chevy version that screws in to the intake, kinda backwards from the norm.   It's not running yet but I'm hoping the vacuum and flow of a late 60 GM six, is close enough.

[Sniper]

PCV's work backwards of how I'd think they would.  minimal flow at high vacuum, max flow at no vacuum.  But if you think of it with regards to blow by, then it makes sense, minimal blow by at idle, maximum at WOT. 

 

https://haynes.com/en-us/tips-tutorials/what-pcv-valve-and-what-does-it-do

 

Keeping that in mind will help you tune the areas most affected.

[D35 Torpedo]

I didn't know that there were major differences in pcvs. At any rate, I put my vacuum gauge inline with the valve and had 7-8 "s at idle. I pinched the pcv off and reset the idle enrichment. Then I popped the top and compressed the step-up spring to soften its rate a bit. These changes made it pretty good. My first attempt, I changed the spring for a soft one and it was terrible. Anyways, hesitation is gone so I'm happy.

[Loren]

From the photo shown, I have a question. Is the other end on the road draft tube plugged?

 

Positive Crankcase Ventilation if not done right is just a vacuum leak.

Vintage Power Wagons sells a kit you might want to examine. Also there are instructions ( Service Informations ) in the down load section of this site.

I believe they are the most down loaded item.

The PCV valve's function is to block the pressure from an intake backfire from the crankcase, so whatever you use you have to make sure it's pointed in the right direction. Otherwise you end up with oil leaks from places you didn't know could possibly leak.

Not to get too into the weeds, but there are two types of PCV systems.

One uses the Oil Filler as a breather, where air can enter the crankcase ( or exit if there's too much blow by )

The other is a closed system which has a tube running from the Oil Filler to the air cleaner, thus anything that comes out of the crankcase gets burnt.

Generally because the Blow By gases have products of combustion and unburned fuel in them, the engine sees what gets sucked in as fuel. So it doesn't need any radical air/fuel adjustments when you add a PCV system.

As I said done right and a PCV system is a very good thing. It removes the water vapor which creates sludge. Most race cars have PCV now days.

[9 foot box]

   That is what I was wondering, from the picture. You can’t have PCV and a draft tube. 

[JBNeal]

additional information - grey beard's PCV installation

 

additional information - partial PCV installation

[D35 Torpedo]

14 hours ago, Loren said:

From the photo shown, I have a question. Is the other end on the road draft tube plugged?

 

Positive Crankcase Ventilation if not done right is just a vacuum leak.

Vintage Power Wagons sells a kit you might want to examine. Also there are instructions ( Service Informations ) in the down load section of this site.

I believe they are the most down loaded item.

The PCV valve's function is to block the pressure from an intake backfire from the crankcase, so whatever you use you have to make sure it's pointed in the right direction. Otherwise you end up with oil leaks from places you didn't know could possibly leak.

Not to get too into the weeds, but there are two types of PCV systems.

One uses the Oil Filler as a breather, where air can enter the crankcase ( or exit if there's too much blow by )

The other is a closed system which has a tube running from the Oil Filler to the air cleaner, thus anything that comes out of the crankcase gets burnt.

Generally because the Blow By gases have products of combustion and unburned fuel in them, the engine sees what gets sucked in as fuel. So it doesn't need any radical air/fuel adjustments when you add a PCV system.

As I said done right and a PCV system is a very good thing. It removes the water vapor which creates sludge. Most race cars have PCV now days.

The oil filler still has the breather, so as to allow the pcv to work, hence the vacuum leak. The former road draft tube is ofcourse capped and is now a pcv housing. 

[38plymouth]

I had one on my car for about 10 years and never could fix the lean situation. I always had a stumble and without finding and drilling out Jets it seemed like it was never going to go away. I pulled the system off a few years ago and the car runs better than ever.

[D35 Torpedo]

2 hours ago, 38plymouth said:

I had one on my car for about 10 years and never could fix the lean situation. I always had a stumble and without finding and drilling out Jets it seemed like it was never going to go away. I pulled the system off a few years ago and the car runs better than ever.

Strange, I like the way it runs now. I made major changes and just messed it up. Went back to what I had and tweaked it, now it's great. It will run leaner, cuz your pulling a lot of fresh air in through the breather, but, I had fattened up my fueling a bit already. 

[D35 Torpedo]

Update, while it's great at temp, cold running needs to be tuned.

[D35 Torpedo]

This whole thread has sent me down a rabbit hole of PCV tech. Seems there isn't a database for this info anywhere, and not surprising, considering there are probably thousands of variations. Would be cool if someone with a flow bench was able to test, and record data on even a dozen common types. 

[DJK]

Somewhere it stated that the oil fill tube breather needs to be replaced with a sealed cap for a properly operating PCV system.

[D35 Torpedo]

4 hours ago, DJK said:

Somewhere it stated that the oil fill tube breather needs to be replaced with a sealed cap for a properly operating PCV system.

This is what I don't understand. If you're pulling vacuum on the bottom end, there needs to be a place for fresh air to come in. Every classic engine I've plumbed has had a pcv and a breather. Usually I'm building V8s, but the same applies. 

[Booger]

Flatties had PVCs???  if thats an oil breather tube then ok

Edited May 24 by Booger
spel

[Booger]

On 5/20/2024 at 8:02 PM, Loren said:

From the photo shown, I have a question. Is the other end on the road draft tube plugged?

 

Positive Crankcase Ventilation if not done right is just a vacuum leak.

Vintage Power Wagons sells a kit you might want to examine. Also there are instructions ( Service Informations ) in the down load section of this site.

I believe they are the most down loaded item.

The PCV valve's function is to block the pressure from an intake backfire from the crankcase, so whatever you use you have to make sure it's pointed in the right direction. Otherwise you end up with oil leaks from places you didn't know could possibly leak.

Not to get too into the weeds, but there are two types of PCV systems.

One uses the Oil Filler as a breather, where air can enter the crankcase ( or exit if there's too much blow by )

The other is a closed system which has a tube running from the Oil Filler to the air cleaner, thus anything that comes out of the crankcase gets burnt.

Generally because the Blow By gases have products of combustion and unburned fuel in them, the engine sees what gets sucked in as fuel. So it doesn't need any radical air/fuel adjustments when you add a PCV system.

As I said done right and a PCV system is a very good thing. It removes the water vapor which creates sludge. Most race cars have PCV now days.

you rock

[DonaldSmith]

When I put in my PCV system, I followed instructions from somewhere in the forum.  I plugged up the oil filler cap, and ran a tube from the oil filler tube to the air cleaner, to supply filtered air to the crankcase.   

 

 

 

 

 

[Loren]

5 hours ago, DJK said:

Somewhere it stated that the oil fill tube breather needs to be replaced with a sealed cap for a properly operating PCV system.

There are two types of PVC systems and they relate to whether the breather is open to the atmosphere or it is a closed system.

The regular filler cap has a mesh screen to keep the bugs out of your crankcase, but it will allow vapor to pass both directions in or out.

A closed system uses a sealed cap which has a hose to the air cleaner. Any vapor going into the crankcase passes thru the air cleaner first. Any vapor which comes out of the crankcase will be captured in the air flow going into the intake and thus burned.

Whenever  you place a vacuum on something it pulls the water vapor out. Water vapor ( along with acid ) is a product of combustion and the source of sludge in the crankcase, so a PVC system is a real good thing. It’s not just emissions, it makes engines last longer.

PVC valves serve to prevent intake backfires from causing oil leaks. There are systems which do not use them. They depend on long small diameter rubber hoses and a fixed orifice to prevent excess pressure in the crankcase. I have also repaired blown seals and pan gaskets on these engines. Not many but it happens.

[Sniper]

5 hours ago, DJK said:

Somewhere it stated that the oil fill tube breather needs to be replaced with a sealed cap for a properly operating PCV system.

 

You have to have fresh, filtered air into the crankcase to replace what is being drawn thru the PC setup.  The oil breather is a filter and can supply that air.  This is exactly how hte factory PCV setup onmy 5 Cuda works, as well as the one that was on my 64 00

 

48 minutes ago, DonaldSmith said:

When I put in my PCV system, I followed instructions from somewhere in the forum.  I plugged up the oil filler cap, and ran a tube from the oil filler tube to the air cleaner, to supply filtered air to the crankcase. 

 

Unnecessary additional work.

[kencombs]

22 minutes ago, Loren said:

There are two types of PVC systems and they relate to whether the breather is open to the atmosphere or it is a closed system.

The regular filler cap has a mesh screen to keep the bugs out of your crankcase, but it will allow vapor to pass both directions in or out.

A closed system uses a sealed cap which has a hose to the air cleaner. Any vapor going into the crankcase passes thru the air cleaner first. Any vapor which comes out of the crankcase will be captured in the air flow going into the intake and thus burned.

Whenever  you place a vacuum on something it pulls the water vapor out. Water vapor ( along with acid ) is a product of combustion and the source of sludge in the crankcase, so a PVC system is a real good thing. It’s not just emissions, it makes engines last longer.

PVC valves serve to prevent intake backfires from causing oil leaks. There are systems which do not use them. They depend on long small diameter rubber hoses and a fixed orifice to prevent excess pressure in the crankcase. I have also repaired blown seals and pan gaskets on these engines. Not many but it happens.

You are correct regarding backfire protection. But, the description of flow direction does not match my understanding.   All PCV systems introduce the crankcase vapors into the intake path, after the air filter.   If the oil fill is sealed and a hose attached from that tube to the air cleaner, the purpose is to filter the air entering the crankcase.   The vacuum from the PCV valve pulls the fumes from the crankcase.  

 

air cleaner to crankcase to pcv valve to intake manifold, is the flow ain my inderstanding.

 

That is what I was taught and believed for the last 60+ years of dealing with them.

[kencombs]

5 minutes ago, Sniper said:

 

You have to have fresh, filtered air into the crankcase to replace what is being drawn thru the PC setup.  The oil breather is a filter and can supply that air.  This is exactly how hte factory PCV setup onmy 5 Cuda works, as well as the one that was on my 64 00

 

 

Unnecessary additional work.

Unnecessary, but that is the path all the later implementations, at least the ones I've seen, seem to go.   Supposedly provides better filtration, maybe of a couple of hundred thousand miles on a newish car it may be better, who knows?

[D35 Torpedo]

44 minutes ago, kencombs said:

Unnecessary, but that is the path all the later implementations, at least the ones I've seen, seem to go.   Supposedly provides better filtration, maybe of a couple of hundred thousand miles on a newish car it may be better, who knows?

I think that style is for a higher emissions standard. Basically for when the engine is shut off after running. Instead of emissions wafting out the breather, they go into the aircleaner and are trapped for when the engine is refired.  

[Bob Riding]

Here is Chrysler's original plan for what they called a "Crankcase Ventilator" system.

PCV p15.pdf PCV p17_p18.pdf PCV air_cleaner1.pdf pcv_p17.pdf

[kencombs]

3 hours ago, D35 Torpedo said:

I think that style is for a higher emissions standard. Basically for when the engine is shut off after running. Instead of emissions wafting out the breather, they go into the aircleaner and are trapped for when the engine is refired.  

except that it looks just like (In flow direction/etc) to that posted by Bob R above .  And the way mine will look, if I ever get it all together.  Chev valve screwed into the manifold or carb adapter, sealed oil filler (or maybe valve covers not sure yet),   the valve cover location will avoid the flying oil in the crankcase.  And the road draft tube blocked.