PCV issues

[Yves]

I experienced a situation where, coming off high rpm, the engine creates a large amount of vacuum and it effectively sucks oil through the pcv into the intake manifold. Now the engine is non-standard so the Original pcv with it's spring actuated pintle is not suited for the engine. I use fixed orifice type PCV with an oil catch can in between.
To combat the situation, would connecting the outlet of the PCV to the airbox (ITB system) be an alterntive ?

[jsmcortina]

You need a sprung PCV when connecting to the manifold. The spring prevents exactly the problem you had.
Or change to no PCV and vent into a can.

James

[Digger]

I experienced a situation where, coming off high rpm, the engine creates a large amount of vacuum and it effectively sucks oil through the pcv into the intake manifold. Now the engine is non-standard so the Original pcv with it's spring actuated pintle is not suited for the engine. I use fixed orifice type PCV with an oil catch can in between.
To combat the situation, would connecting the outlet of the PCV to the airbox (ITB system) be an alterntive ?

What makes a spring-type not suited for you engine?

There are adjustable type out there too.

[Yves]

Can you point me to one. At the time I was checking into these I only found the ones that you couldn't set.

[Yves]

You need a sprung PCV when connecting to the manifold. The spring prevents exactly the problem you had.
Or change to no PCV and vent into a can.

James

The pcv's for my engine have a 3/4" hose and no regulation of the spring force. What happens is they are full open at anything except decel which acts as a very big vacuum leak.

[turbo conversion]

You need a sprung PCV when connecting to the manifold. The spring prevents exactly the problem you had.
Or change to no PCV and vent into a can.

James

The pcv's for my engine have a 3/4" hose and no regulation of the spring force. What happens is they are full open at anything except decel which acts as a very big vacuum leak.

I am confused, if your PCV valve has a spring it should be closed under full throttle and wide open under decel.

How exactly do you have your PCV valve system plumbed?

David

[cactus]

I've been curious to hear other impressions about this adjustable PCV valve.

http://mewagner.com/

[billr]

"I am confused, if your PCV valve has a spring it should be closed under full throttle and wide open under decel."

Yes, I think you are confused. That is opposite to all I have worked with, and that goes back to when they first became required in 1965.

[turbo conversion]

Are you saying with out vacuum the valve is open and with vacuum the valve is closed?

David

EDIT: I am not talking about the breather side but the valve it self.

[jsmcortina]

See https://en.wikipedia.org/wiki/Crankcase ... or_orifice

James

[billr]

Yes, manifold vacuum closes the PCV valve to restrict flow. It has to be installed in the correct direction though...

All PCV valves I have seen have just a single hose barb for the hose to a manifold, with the other end going into a grommet on the engine; so installing "backwards" would be a very difficult mistake to make.

[Yves]

I've been curious to hear other impressions about this adjustable PCV valve.

http://mewagner.com/

This is the one I have

[Yves]

Yes, manifold vacuum closes the PCV valve to restrict flow. It has to be installed in the correct direction though...

All PCV valves I have seen have just a single hose barb for the hose to a manifold, with the other end going into a grommet on the engine; so installing "backwards" would be a very difficult mistake to make.

Of course...

However the spring is set according to engine vacuum. If your vacuum is lower than what the engine for which the valve is designed for has, then it's going to stay open.

[billr]

Then you need a PCV valve with a weaker spring, or a better "adjustable" one. Just how bad is your idle vacuum?

[Yves]

8 inchHg

[billr]

That should be enough. If I had to, I would cut open a stock valve and change out the spring; make my own "adjustable" one.

[turbo conversion]

The article James posted says under high vacuum the valve moves against the spring restricting vacuum, it does not close the valve.

At full throttle or atmosphere the PCV valve does not have vacuum rendering it ineffective hence the breather side now acting as the vacuum source.

If you put a catch can in the the PCV valve side and the breather side you can eliminate oil in the intake manifold, that's all I have to say about that.

Forest Gump

[Yves]

The breather clearly doesn't stop the oil being sucked through.

[turbo conversion]

The breather clearly doesn't stop the oil being sucked through.

That is why I use 2 catch cans.

David

[Digger]

8 inchHg

That's your problem. You don't have enough vacuum to shut or throttle the valve at idle, making your PCV unsuitable for your setup. However an orifice is not the answer either. You need to buy a PCV valve that is matched to your idle vacuum or buy an adjustable.

Also important, do you have proper baffling in your valve cover? This will also cut down on the amount of oil sucked into the intake.