do you need PCV ?

[DanEC]

For what it's worth, my 64 Plymouth Sport Fury/383-4bbl had a PVC system from the factory and so does my 66 427 Corvette and 67 Plymouth GTX, so I know they were in widespread use well before 68.

I need to do something with my intake rear mounted breather because it will interfer with my heater hose. Running a block off plate with a nipple piped to the carb vacuum is one option. Have most of you who have done this installed some sort of check valve in the tubing to function as a PVC valve - or just run an open line to the carb?

[Texasdoc]

How do I figure out which PCV valve to run? Some are labelled with a letter A thru F. Most aren't. They guys at O'Reilly just ask me what car it is going in an try to look it up on a computer.

Brent, what PCV valve do you suggest in a 408W pushing 400hp at the wheels?

[blykins]

I recommend not using any.....

BTW, if you've noticed, in 4 years I've changed my thinking....LOL

Doesn't hurt to run one, but over the course of the years, I've resorted back to the KISS method.

[lippy]

I like the idea of having a PCV. You may want to look at this: M/E Wagner Performance Products | High Performance Crankcase Ventilation Systems. I just installed one, along with a Moroso oil/air separator. Expensive, but it works well. Otherwise, with an aftermarket build, you are essentially guessing at which valve is appropriate and you have no idea how much of the time it's actually open.

[1795]

You ask have to take a look at your states emissions regulations. If the engine would have had a PCV valve based upon the year of the engine or build, you may need to have one.

[DWRAT]

Originally Posted by blykins

I recommend not using any.....

BTW, if you've noticed, in 4 years I've changed my thinking....LOL

Doesn't hurt to run one, but over the course of the years, I've resorted back to the KISS method.

What is the KISS method?

[Phx Mike]

I just have two breather caps on my FE - No PCV - and no trouble so far. I don't think there is any downside to a PCV system but emissions aside there is no harm in not having it either.

[Gaz64]

Originally Posted by DWRAT

What is the KISS method?

Keep It Simple Stupid.

[blykins]

Gaz nailed it....

Mike nailed it too. There's no harm in using one (if it's chosen correctly and it's functional) and if you live in a Communist state where they check stuff like that, then you have no choice.

Otherwise, over the years I have seen bad PCV's that have caused oil usage and have struggled with finding correctly size valves for engines that have never existed in OEM form.

Back in the day, there were no vents, PCV valves, etc. Engines had road draft tubes and they vented pressure by dumping oil on the road. When the government decided that had to change, auto manufacturers began to come up with ways of dealing with the crankcase pressure. The PCV valve was the most emission-friendly as it put any vapor right back into the engine to be recirculated.

It's a lot simpler to just run 2-3 valve cover/intake breathers to make sure the engine can vent and it will not cause a problem down the road since there are no valves to fail. If a valve does fail (or is incorrectly chosen), it will allow the engine to pull oil into the intake under higher manifold vacuum levels.

[DanEC]

My first car back about 68 was a 64 Plymouth Sport Fury (5 yr warranty on drive train as I remember). It was using oil and fogging the rear bumper pretty good so Plymouth pulled the motor down and re-ringed it under warranty. Still smoked when it came back. Turned out it was a bad PVC valve and replacing it fixed all the oil and smoke issues.

[G-Pete]

On a PCV is nothing positive...

[moore_rb]

Originally Posted by Phx Mike

I don't think there is any downside to a PCV system but emissions aside there is no harm in not having it either.

The only possible downside is the potential for oil consumption in a poorly designed PCV layout, like Brent mentioned above, which usually arises when a PCV valve is plugged into a non-baffled valve cover.

I totally agree with Brent that venting directly to atmosphere (typically out of both valve covers) is the easiest solution for engine longevity and design simplicity. That is the answer to the OP's question- No, you don't "need" PCV- but you do need a way for crankcase vapors, and the pressure they generate, to vent out...

[olddog]

The PCV valve was the greatest invention the environmental movement spawned.

The blow by vapors stink! You ever get a good whiff, you will understand.

Imperceptible oil vapors will slowly over time coat everything attracting dirt grime and slowly breaking down wire insulation.

I would think a T in the line going to the brake booster, would allow you to connect the PCV valve. You might add a vacuum canister with a check valve in front of it to make sure the brakes have plenty of reserves, if it doesn't have that already. Verify I am not full of it, because brakes are more important! Use my idea at your own risk. I do not know everything and comment freely to inspire thought. It is not advice.

[lippy]

Most of the information I have indicates that burning off crankcase vapors with a PCV is better than keeping it in the crankcase because it can contaminate your oil fairly quickly. I guess that's not a problem if you change your oil every race but in a street car if you want to keep your oil for 2-3k miles, it's a factor.

Also, to me, keeping negative pressure in your crankcase seems like a good thing for seals and gaskets.

I agree with what Brent said about problems with the wrong sized valves or ones that for some reason don't work. That is why I went with the adjustable ME Wagner one.

[DanEC]

Power brakes?

[Bernica]

Originally Posted by DanEC

Power brakes?

You beat me to it Dan!

[blykins]

Most of your "elevated" crankcase pressure is going to be at WOT. At that setting, your PCV is not creating negative pressure. I suppose that at idle and part throttle there is some vacuuming going on, but the amount is based on how much manifold vacuum you have available at that rpm.

[moore_rb]

Originally Posted by blykins

Most of your "elevated" crankcase pressure is going to be at WOT. At that setting, your PCV is not creating negative pressure.

Exactly- Which is why a PCV system will always have a vent line on the other valve cover going to the air filter, or through a filtered breather.

PCV only opens the valve and pulls the vapors out when engine vacuum is high.

When engine vacuum is low (WOT) the positive crankcase pressure is venting out the non-pcv fitting(s) in your system.

[olddog]

On newer EFI engines, I believe, at least some, manufactures went to a closed system, where they removed the vent on the opposite valve cover and plug it off.

I have heard different theories, as to why. If you evacuate the air from the crankcase there is less energy wasted spinning air. It reduces the amount of air pulled into the EFI system that is not measured.

I do question a closed system at WOT. It takes little pressure to push oil under a gasket.