PCV valves are rated at different amounts of vacuum, so I'd use one that is from an engine with similar vacuum. I'd use one from a high hp 327 for low vacuum situations.

 

Or just put a breather on it and throw the PCV valve away?

 

Then you might as well throw the engine away while you're at it.

 

Uh oh....

Swing and a miss Powertripin' LS motor man.

I concur with Mr. Goble, USE one (reduces blow by, keeps your engine seals where they belong) off of a high horse motor.

Kev

 

What is your deal? I'll give you my autograph if you want, christ, Just quit sending me PMs for my phone number.

You start getting into modified engines you do away with the PCV valve, cam/vacuum.
Sucking back in that crank case gasses mixed with an oil vapor isnt very performance oriented. If you need something run a crankcase evac kit, tubes running to your exhaust, or some people run pumps. I dont have all the scientific formulas but go to the track and get a general census. See what cars still have the PCV valves in them and what ones dont, and whos running what....you wont see many PCV valves unless your looking at mostly stock type cars.

Lots of people run just breathers and its perfectly fine. No PCV on my car and 2000 miles with mobil 1 and its still clear.

 

how can i determine if "this" valve is suited for my needs ???

i want to use an inline 3/8 valve.

maybe a dumb question... would a 4 banger have a different vac rating than a sixer, compared to a V8 ??? if i have no real specific application to ask for how do i determine the correct valve ???

i know i can get access to a catalog but if memory serves correct they don't list the vac ratings of the valves.

what will the symptoms be if i use the incorrect valve ???





Thanks for the help.

 

Buy one, install it and see how it works. It should be mostly closed at idle and open more under load. If you use a valve made for higher idle vacuum than you have, you will get too much flow and disrupt your idle mixture.

 

Mike,
Can you please tell us how to check and see if it's working correctly? How do you know if it's clossed at idle? How do you know when it's opening? Thanks in advance for the education!

 

i dont remeber the number system they use but they are all numbered on the bottom. which you can cross ref to a vac chart.

 

a guy with a high rpm small block here on long island ,installed a pcv vacuum pump, gained 30 hp to the wheels. on the dyno. if i hadnt seen it i would believe it. it scavenged so much pressure out of the motor.

 

Holy crap this thread was hijacked thank god I have a breather only motor that I am going out tomarrow and buying a pvc valve and fitting Damn there goes my matching breathers

 

What # pcv valve do you know to get?

 

That "steam" is blow-by gasses. Breathers are supposed to draw air into the engine not expell it. Blow-by will eventually look like black sooty spider webs coming out of the breather. That's how you can tell if your PCV valve is working. If it's working correctly, there won't be any black soot or oil coming out of the breathers because they are drawing fresh air into the crankcase like they are supposed to.

With a later-style engine, you want to run a PCV valve on one valve cover and a breather on the other valve cover. You don't want to run a breather on the same valve cover as the PCV valve or else you will just "ventilate" the one valve cover instead of the entire crankcase.

 

Bear with me as I tell a PCV valve story----

Years ago, as a rookie parts man (about 25 years ago) a technician came to me needing a Chevette pcv valve. He was changing it as routine maintenance. I didn't have the correct one, so we matched on up by eye.

Within a couple of weeks, our customer was on the line, screaming "What did you do to my Chevette when you changed the oil. I can't even get a tank of gas burned for every quart of oil I burn. It was perfect before you changed the oil."

We HAD put in the wrong valve. We ordered the correct Chevette valve, installed it, and problem solved.

You can call BS on this if you like, but I still work with this tech today, and we both still have the occasional good laugh about this "oops" of mine.

 

I would still like to know how you figure out which PCV to get for a modified engine. Do you put a vacuum guage on it and go by that?

Dave

 

I wish I knew. I have always just ordered for the closest factory combo possible.

 

If your engine produces a strong vacuum signal at idle, you should be able to use a common V-8 PCV valve. If you are running a radical cam, you will need to select a PCV valve from a high-performance engine that had a lower vacuum signal like the '69 302 or another high-perf engine. When you plug the PCV line and then unplug it, the idle should not change radically if you have the correct value. If the idle increases significantly or becomes rough, the PCV valve is open too far at idle.

A PCV valve should be replaced frequently. They do wear-out and I usually replace mine every time I do a major tune-up or every year or so. The old shake and rattle test won't tell you if the PCV valve is any good. If you start to see oil or blow-by at the breather, you know the PCV valve is bad. If you have to make idle adjustments like the mixture screws or the speed all of a sudden, the PCV valve is the first thing to check.


Here's a pretty good tech article on how PCV works:

http://www.magnumproducts.com/faq.htm

 

Very educational article.

 

So then how good is this pcv valve from moroso and what vehicle would you use it on? It is generic so it sounds like any vehicle could because of the disc instead of check ball, but then that is why I am asking..

http://performanceparts.com/part.php?partID=4540

 

the link you've posted is for a breather...

in the automotive aftermarket, that cap looks very similar to what comes on Mopars.

 

My past experiances with a PCV is run one if you can, but during high speed running there is less vacumm in the engine to even make a pcv work at all. Also as in my case with the sheet metal valve covers, I have no room between the stud girdle and the valve cover for any baffles to keep the pcv from sucking every drop of oil as it goes by the valve. I run a soild roller with out the restrictors in the block to get more oil to the top to keep the springs cooled down and prevent fatigue and breaking which works very well. I haven't come across any way to possibly run a pcv, any suggestions as to what anyone else has ever done. The last 6 high perf. engines I have built have never got a pcv and they have never had any troubles what so ever with leaks and such, but I am a believer in them if you can run one, but it will not trash the motor if you don't. Just my experiance I guess, the engines I build don't have any noticeable blowby either, there is never any mess around the breathers or anything.

 

most people in your situation have it tied into there exhaust, down by the collector..but its still not a pcv system

 

A lot of all-out race engines use oil separators and vacuum pumps at constant high-RPM operation to evacuate the blow-by without losing oil.

 

Man this thread is some good stuff. I went out and got a pcv valve and swapped it with the passenger side breather. I used the valve that was listed for most BB applications in the late 60's early 70's. When I started the car and let it warm up I noticed an improvement in idle quality and the engine runs smoother. This is an excellent thread.

 

That's what this site is about. Helping other members get the most out of their Novas and shattering the myths that we've all grown up with. Your engine will thank you for evacuating the nasty corrosive blow-by gasses by lasting a lot longer and performing better.

Make sure you change that PCV valve regularly as part of your routine tune-up. They're inexpensive.

 

my valve covers have no baffles in them wont this suck oil like a oil vampire??
What should I do

 

Moroso makes a rubber grommet baffle for valve covers that don't have them for breathers and PCV valves. They will only fit tall valve covers though. I used to use them in a pair a valve covers I had.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=MOR-68772&N=700+115&autoview=sku

http://store.summitracing.com/partdetail.asp?autofilter=1&part=MOR-68775&N=700+115&autoview=sku

 

Thanks now I know what I need to buy

 

It's not a PCV system, but it is a crankcase ventilation system that accomplishes the same thing. It's a draft tube.

 

Yup and thats what I run on my 13.5:1 383 stroker in my camaro.

 

so does that hose go to a bung in the header or collector? Wouldn't that be actually better than a pcv since there is no chance of oil getting in the intake?

 

There is a hose on each side going to a bung welded in at an angle on each collector. As the exhaust gas passes the bung it created vacume and evacuates the crankcase. On the bung thats welded in is also a one way valve which prevents pressure from being forced back into the engine in case of a backfire etc etc etc. And yes I feel it is a much better setup than a pcv system but it is overkill for a normal street engine but it surely wont hurt anything and I think it looks cool to. I just wish I had braded hose on mine which is on the list of things to do in the future. .

 

It's your engine.

 

Yes you are correct! and it does alright the way it is.