pcv valve

[390owner]

Will it hurt my 390 to have a vent in each valve cover and NO pcv valve

[machoneman]

No, it won't but by not having the valve, your engine compartment will get oil on a few things, leaving a thin, oily film. That and you may smell more oil vapor at a stoplight or even while driving. No harm running a PCV valve.

[jayb]

There can be harm running a PCV valve, if your engine is on the brink of detonation.  Oil mist is sucked into the intake tract with a PCV, and that makes the mixture more prone to detonation.  I never use PCV valves for that reason.  Also, use of the PCV valve does not automatically remove oil mist from the engine compartment, sometimes you will get mist out of the lone breather anyway.  A PCV valve will improve that situation in most cases, though.

A better,  albeit more complex solution to this issue, is to use a pan evac system, where the valve cover breathers are connected to tubes that run down to the header collectors.  In that case you don't have any crankcase openings to the engine compartment, so no oil mist, and no oil gets into the intake tract to encourage detonation.  Plus you get the added benefit of a few inches of crankcase vacuum.  I've had good luck running those systems on the street and at the track, but it's a lot more work to install.

[philminotti]

I had one attached to a vacuum source at my EFI throttle body... The same location as I was getting vacuum for my MAP sensor and fuel pressure regulator reference.  Guess where the oil ended up?  In my MAP sensor and fuel pressure regulator.  I got rid of the PCV. Vented valve cover is all I have.  No problem.

[cammerfe]

My first brand-new car was a '64 Custom with a 427. It had a road draft tube.

Some years later I got on a Pinto kick. (Even bought one new and ultimately installed a 429 SCJ that had a 460 crank in it, etc.) Bought a Pinto used, to be a daily driver for a while, that had bad valve guides and crackled like crazy even on premium gas. Finally changed the head to keep oil out of the combustion chambers, and lost the crackle. Jay has it right about the detonation proneness of a fuel charge with an oil mist component. I've never been really in favor of the PCV bandaid.

KS

[390owner]

My engine was using a quart about 600 miles fresh rebuild. I removed the pcv valve and so far the oil has not moved on the dipstick. It was also pinging up every hill until I had the timing so slow it was sluggish. It has not pinged since and I have advanced the timing a couple of degrees. May go up a little more and see what happens

[390owner]

So how does this pan evact system work

[jayb]

Moroso has the one that most people use, called a Pan Evac system.  You have to weld a special pipe, that kind of looks like a whistle, into the header collector on each side.  Then you use the breather caps that come with the kit, which have a tube coming out, and connect the tube with a hose down to the pipe on the collector.  The way the pipe is installed it creates a vacuum in the pipe during part of the combustion cycle.  A one way check valve is installed in the hose, so that pressure from the exhaust can't push back into the engine through the hose, but a vacuum is created at some times in the hose. The effect is to provide some suction on the crankcase. 

[afret]

Like Jay said, hook up a pan vac system.  You just need to get a breather cap on each side that you can hook up a heater hose to and attach it to a fitting that comes with the pan evac kit that you weld to the exhaust on each side.  The instructions tell you to weld it to the header collector but I found that it doesn't really matter and you can weld to to a convenient spot on your exhaust pipe.  I think you need to have straight through type muffler for the system to work well.  Mine works great and has quite a bit of vacuum.





Use the breather caps that are tall and not the short ones like these in the photo below.  Under hard acceleration, the right side can suck oil.

[390owner]

I will check it out I have never heard of that set up but looks like it would work great. Thanks

[GerryP]

I will check it out I have never heard of that set up but looks like it would work great. Thanks

They've been around in the public eye for around 50 years.  It was Pro Stock tech back in the day.

These systems are very effective at pulling down a crankcase.  Not so much at low rpm/load due to the lower gas flow but overall they work just fine on a street exhaust system with full mufflers and pipes out the back.

If you don't think about the physics, it seems counter-intuitive that a pipe in an exhaust system that has positive pressure could draw a negative pressure.  But it does.  You can test this theory yourself by putting a straw in a glass of water and blowing across the top of the straw.  You'll find that with the tip of the straw at a certain angle, the water will rise in the straw.  It's really just a simple siphon.  I think it's Bernoulli's principle that makes it work but not for certain there.

So, you have this tube you stick in the exhaust pipe and there you go.  Mostly but not quite.  The tube is actually an aspirator tube.  It has an angle cut on the end.  The tube has to be inserted into the exhaust at a certain angle so that the gas velocity will increase as it moves around the tube, creating a vacuum.  So, again, getting back to the simple siphon, it's not the pressure in the exhaust pipe, but the velocity of the gas moving past the aspirator tube that sucks out the crankcase vapors.

There are more complex variations of this that do involve a PCV and check valves in the system to handle low speed evacuation, but I think that's a bit over-done since you probably don't spend all that much time at idle to where it would present a problem begging for a solution.

[gregaba]

I think pvc valves are junk and don't do what they are suppose to do. You are buying 1961 tech with very few improvement since.
You go to your local parts store and order a valve for a 68 428 and the list will be for tons of other engines it is listed to work on.
At best a bad compromise.
I have been bypassing them since the 70's and aside from a slight oil smell after sitting at a long traffic light no problems.
One of my pet peeve's.
Greg

[cjshaker]

They're not totally without their uses. For mild or stock street engines that get driven in winter months, high humidity areas or are short tripped, they do keep moisture from forming acidic compounds in the engine. I'm sure most of us, at one point or another, have seen the "milkshake" goo that can accumulate on oil fill tubes or around breathers from moisture reacting with the oil. PCV's will generally stop that from happening. Trying to filter the vapor as best you can, before it goes into the air cleaner, is a very good idea. There are oil separators that are available for newer engines PCV systems that can be adapted to any engine. Guys with Mod motors have been using them for years to deal with the issue.

Having said that, I'd never use them on a performance engine that requires a high octane fuel. It's asking for a problem, in my opinion.

[drdano]

This is a great thread.  I've been running this Moroso oil separator in conjunction with the rest of my PCV system and it does seem to give me a shot glass of oil each time I remember to empty it.  I may go the pan evac route mentioned here and ditch this setup since I need to fabricate new exhaust from the headers to the x-pipe soon. 

Do you guys running this setup notice additional tailpipe smoke at all?  I assume this must be installed down from the O2 sensor, correct?

[cjshaker]

Do you guys running this setup notice additional tailpipe smoke at all?  I assume this must be installed down from the O2 sensor, correct?

Definitely past the O2 sensor. It would foul it up fairly quickly.