Breathers and PCV valves

[Gael]

My setup looks sorta like that picture.

On the drivers side, I have a PCV towards the front of the engine, which the tubing runs back into the carburetor.

On the passenger side, I have a breather. Works fine for me.

 

[76_Cobra_II]

So the way I have it is fine then? I also noticed while looking at it that I need to get some valve cover gaskets, My spark plug wires on the drivers side are covered in oil.

 

[Wart]

Mine doesnt look like this at all.... Mine has the push in filter on both sides. Is that bad? I bought it that way and I dont know any better if its wrong.

There are filters and there are breathers, they aren't the same.

A filter has filter material and is meant for use with a PCV. It filters the air being drawn into the crankcase.


A breather has material simular to this:

A heavy wire mesh. Breathers are meant to allow the passing of blowby. There is no real need to filter as everything going through them is from inside the engine. The mesh is there to keep big things like bugs and stones from getting in the engine, it's more like a strainer.

Using a filter as a breather can lead to posative crankcase pressure. The filter will eventually get wet with blowby and not allow it's passage as easily. Could lead to leaks.

One downside to a breather is the heavy metal mesh condenses the water in blowby. The engine has to run long and hot enough to re-evaporate this water else there will be breather cap mayo.

Venting the crankcase to atmosphere has the slight problem of covering the inside the engine compartment with oil. If your a 'primper' you'll notice this almost immediately. On a heavy huffer you'll also notice the odor of oil laden air.

 

[Wart]

OH, and when Istep on the brake pedal, I can hear my engine rev up just a little bit every time. Maybe just enough to be a 1/2 to a full RPM. Is that bad?

50 to 100 rpm?

That's somewhat normal.

As your sitting there with your foot still on the brake do the revs drop? They should.

 

[Blue Thunder]

No.

I would rather have full manifold vac applied to the booster.

I also like having a dedicated source for the booster.

Something about having my booster getting it's vacuum in a blead air circuit. Especially since the bled air is controled by a cheap valve. How much vac will that valve allow to be created anyway? Probably enough to work the brakes long as the engines running.


Finally, it's poor form.


If it works for someone else good for them. Hope they have strong legs.

Well, the highest vacuum signal comes when you let off the gas after cruising, and the one-way valve in the booster holds that high vacuum until it's needed. You get one good solid blast of power assist just from the stored vacuum. Anyway, my engine only makes 7" of vacuum at idle, so I only have whatever is stored in the booster to use at any given moment.
As for that PCV valve, it works via a fluttering weight, and almost all parts stores will give you a PCV valve that's weighted for the intake pulses of a small block chevy. The small block Ford has a different intake pulse pattern, and so requires a PCV valve with a different weight. With the correct PCV valve installed, the vac loss is slight, and the engine will deliver roughly the same vacuum to the booster even with the PCV leeching.

 

[Blue Thunder]

Mine doesnt look like this at all.... Mine has the push in filter on both sides. Is that bad? I bought it that way and I dont know any better if its wrong. I have a 4B Edelbrock carb and manifold. Aftermarket open air cleaner that is like 8" around. I do notice that it doesnt take long for steam/smoke to be seen coming from the push in filter caps. LET ME KNOW! OH, and when Istep on the brake pedal, I can hear my engine rev up just a little bit every time. Maybe just enough to be a 1/2 to a full RPM. Is that bad?

You have a passive system, not a PCV(positive crankcase ventilation) which doesnt really do much of anything to evacuate the exhaust gases that blow past the piston rings and accumulate inside the crankcase. Exhaust gases in the crankcase causes the oil to become contaminated much more quickly than if you're running a PCV system. Without a proper PCV system, you should change your oil every 500-1000 miles max.

When you hit the power brakes, it causes a sudden vacuum leak to the engine as the brake booster begins to refill itself with manifold vacuum. At the same time, the drop in vacuum causes the vacuum signal to drop in the carb venturis, which opens the power valve in the carb's metering block(s), and therefore temporarily enrichens the air/fuel ratio.
To tell you the truth, I'm not certain if it causes an overall lean condition from the vacuum leak into the booster, or a rich condition from the power valve opening. Either way, the changes in vacuum will affect your idle.

 

[Wart]

Well, the highest vacuum signal comes when you let off the gas after cruising, and the one-way valve in the booster holds that high vacuum until it's needed.

LMAO!

Hey, Bud, whatever works for you.

Honest Officer, I had just backed off the throttle which means I should have had enough 'signal' (?) in the booster to stop!! I must have used up my 'one good shot' the first time I hit the brakes, the second time the pedal felt like a stone! It's not my fault.

Seriously, that's pretty funny.

You can rationalize your set up any way you want, I would hate to see anyone else follow your ..... form.

 

[Wart]

When you hit the power brakes, it causes a sudden vacuum leak to the engine as the brake booster begins to refill itself with manifold vacuum. At the same time, the drop in vacuum causes the vacuum signal to drop in the carb venturis, which opens the power valve in the carb's metering block(s), and therefore temporarily enrichens the air/fuel ratio.
To tell you the truth, I'm not certain if it causes an overall lean condition from the vacuum leak into the booster, or a rich condition from the power valve opening. Either way, the changes in vacuum will affect your idle.

So, hitting the brakes drops MAP to just about atmospheric pressure?

I don't think so.

Read up

 

[Blue Thunder]

LMAO!

Hey, Bud, whatever works for you.

Honest Officer, I had just backed off the throttle which means I should have had enough 'signal' (?) in the booster to stop!! I must have used up my 'one good shot' the first time I hit the brakes, the second time the pedal felt like a stone! It's not my fault.

Seriously, that's pretty funny.

You can rationalize your set up any way you want, I would hate to see anyone else follow your ..... form.

What the hell are you talking about?

Anyway, if you have chicken legs, maybe you'll have issues with stopping a car without power assisted brakes.
That aside, with an engine making decent vacuum and the PCV leeching from the brake booster, the power brakes will function perfectly, regardless of whatever strange notions you have in your mind.

 

[Blue Thunder]

So, hitting the brakes drops MAP to just about atmospheric pressure?

I don't think so.

Read up

Again, what the hell are you talking about?
I said that hitting the power brakes causes a sudden vacuum drop in the manifold, which opens the power valve.
Taken from the very link that you posted, "the power valve selected should have a vacuum opening point about 2" Hg below the intake manifold vacuum reading taken."
Gee, I guess that says when the vacuum drops 2" or more, the power valve opens?

What the hell does this power valve function have to do with the "MAP dropping to just about atmospheric pressure?"

By the way, thanks for that holley tech link, it looks vaguely "familiar" to me for some reason. heh.

 

[Wart]

Again, what the hell are you talking about?
I said that hitting the power brakes causes a sudden vacuum drop in the manifold, which opens the power valve.

Where in the hell did you come up with this? You do realize if by applying the brakes raises MAP to the point the power valve opens there are some real problems that need addressed?

Seriously.

Maybe if the engine needs 23" to idle hitting the brakes may be enough to pop a 65 valve, but not in a normal engine that needs only 9 to 15".


What we have here is someone trying to give advice from their narrow experience, not how it applies to multiple cases within the norm. This isn't unusual.

What the hell does this power valve function have to do with the "MAP dropping to just about atmospheric pressure?"

Geez, you didn't catch I got that backwards?

MAP raises to just about Atmosphere.

What does that have to do with valve operation??

 

[Wart]

Anyway, if you have chicken legs, maybe you'll have issues with stopping a car without power assisted brakes.

Come on, Blue Boy,

You can't be that frigging absolutely clueless. ?

 

[Wart]

Another example of someone putting something together with the assumption nothing will go wrong, everything will work as planned.

This mind set works on a track. Nowhere else I'm aware of.

When I repair or build something I look at it as having to manage traffic on the street. Day to day driving where things oftenly go wrong and there is no plan except planning for the worst.

Take it to the track, have fun. Drive it cross town at rush hour? Could be too much uneeded excitement for me.

Brakes have to be relyable and consistant.

 

[Blue Thunder]

That's interesting, as I've been driving my "track" car on the street since '89, with no issues with brakes so far. I've also been building/repairing cars since the late 70s, and no issues with brake functions yet.

But hey, whatever floats your boat, wart. Build yourself a good brake system and be happy.

 

[LedZ 5.0]

Very interesting. I know that when I bought my 75 the brake booster was connected to the base of the carb and the pcv was connected to the vacuum tee on the rear of the intake. That's been almost two years that I ran the car this way and had no problems with brakes or loping ide. I left it alone.

Today I removed the carb to check the inlet needle seats and to see if there was any dirt in the bowls. Also changed out my plugs after two years. The Accel u-groves hold up well.
I decided to switch the hoses to their proper connections. The booster hose to the t fitting at the rear of the intake and the pcv hose to the base of the carb. I fired the car up and there was some surging at idle. I will find out more once I take it out one day for a test run.

Just wondering why now there's a surge.

If it keeps surging at idle once I test run it than I'll switch the connections back to where they were.

 

[Wart]

Very interesting. I know that when I bought my 75 the brake booster was connected to the base of the carb and the pcv was connected to the vacuum tee on the rear of the intake. .....
I decided to switch the hoses to their proper connections. ....I fired the car up and there was some surging at idle. ....
If it keeps surging at idle once I test run it than I'll switch the connections back to where they were.

What is the outcome?

 

[LedZ 5.0]

What is the outcome?

There's no difference in vacuum reading or brake operation. So I will leave the connections where they are.

The surge at ide was the idle mixture settings. I left the engine warm up to operating temp and set the mixture screws right around 1 & 1/4 turn out where my idle was the smoothest. The car seems to run a little better with the new plugs.