PCV Valves

[nevermind65]

I'm just curious as to whether anybody runs a PCV vale on their engine. I hooked one up to stop the oil smell coming from the valve cover, but now, due to only having about 10 inches of vacuum, the car wants to stall. I was at Autozone and they have like 50 different variations.

Did anybody use a specific one for an engine with a hefty cam and no vacuum?

[Bob In Ct]

You really don't need one. Put a breather on both valve covers.

Bob

[Ron61]

I have them on all of my engines and have never had a problem. And the BB has a pretty radical cam with low vacuum. But as Bob said, you can just use two breathers. But you will have to wipe up the oil residue every so often normally.

Ron

[vettestr]

As the guys have said it can be plumbed with or without but you must have system vented in some manor. If you do not vent or use suction to remove gasses from engine it will build pressure in crank case and cause leaking.

Be mindful of where you pick up vac in the manifold. Although a properly functioning PCV is not a vac leak it does consume vac and can lean out a cylinder at low RPM. The best source or location to tap into the manifold is near the carb/s or a large plenum area as it has a dampening affect. If you use the port on a single runner in the manifold near the head it pulls from that cylinder and not the common area of the manifold.

A PVC valve is as a hose with a built in valve that shutters on and off. The on time allows suction to remove a volume/unit of gasses so no pressure can build up in the crank case. The off time keeps it from causing the mixture of fuel and air from getting to much air making the mixture lean.

[nevermind65]

Thanks for all the replies.

I found a PCV valve lying around from a 5.0 liter. I swapped it out with the one I bought from Autozone. Seemed to do the trick. The one from Autozone, that I just randomly grabbed off the shelf, had a huge orfice. My guess is that it was allowing too much vacuum to be lost. I guess there is a reason they have 50 different variations.

I believe there is no valve per se in the PCV valve. Basically it is always "on" as long as your engine has either vacuum, or pressure in the engine. The rattling you hear does nothing but act as a one way valve so if you should encounter a backfire and an open flame is present, it will not allow the flame to travel into the engine where oil mist is present causing an even larger fire. That is what I was told many years ago anyhow. Maybe the valves for newer cars have something different in them?

Thank you!

[PaulProe]

has anyone found a site that lists the parameters of the different PCV valves and how to select one?

The outside-physical shape is one thing. Once you've found the correct configuration, there still are 20 different valves to chose from.

I've looked all over the internet and manufacturers site but no luck. Surely there is a site somewhere that outlines the valve selection process

Paul

[Clois Harlan]

I have been told that unless you are strictly racing you should run a PCV because it keeps your engine a lot cleaner. I run one on all my cars even when I put it on the track.

Clois

[vettestr]

Too find a PCV valve I might suggest looking up a muscle car in the approx. era of your engine and your cubic inch. As far as testing or design this is as close as I can get http://www.qualitymag.com/CDA/Articl...100000f932a8c0____

[jdog]

No pcv valve for me!

Dual breathers.




Like Ron said, I just need to wipe her nose every once in a while!

jdog

[mr0077]

Nevermind, the PCV valve closes as much as it can (slight air flow) when there is high manifold vacuum (like at idle), and opens when the vacuum is low (like accelerating). The vacuum pulls it "closed" and the spring pushes it open when it can overcome the vacuum signal. That way, it has minimum effect on the fuel/air ratio at idle (assuming it is hooked to the plenum and not a runner) and works only at higher engine RPM. I agree with Clois, I think it is almost a must on a daily driver, and highly recommended on any street vehicle.

[BDR561]

Would venting both valve covers (with a PVC) into the air cleaner base provide enough vacume/venting for gases?

My application has a high lift cam which provides low vacuum. Venting alone has me wipping off the oil film from the covers after hard runs. Just looking for a clean, but effective look.

Second option would be vent one side to the air cleaner base, and the other to a catch can or both to a vented catch can.

Recommendations?

[mr0077]

If you vent both valve covers into the air cleaner you would not need or want a PCV valve in one of them, since there wouldn't be any vacuum to actuate it and it would simply plug one hose. I guess you could hook up hoses between the valve covers and the air cleaner (no PCV), but you wouldn't get the benefit that a typical PCV hookup has.
Typical application has a PCV valve on one valve cover and either a vent hose, to the filtered side of the air cleaner, or a breather on the other valve cover. Under normal use the vacuum pulls vapors from the crankcase through the PCV into the engine (except at idle). The vent hose supplies filtered replacement air into the crankcase at the other valve cover for crossflow ventilation. Under hard use, with the vacuum near zero, the PCV is essentially non-functional and any excess pressure that doesn't go through the PCV is vented into the air cleaner through the vent nose and pulled into the engine there, or out the breather (possibly making a little mess on the valve cover). If you're getting a big mess at the breather, there may be too much excess crankcase pressure (blowby or?), and the hoses would be a better choice than a breather.
A normal setup should work for you unless you have less than 5" of vacuum. A breather on one valve cover works well for me and is simpler than hooking up a vent hose to the air cleaner.

[rdorman]

PCV valve is one of the few win-win in emission controls. I run a completely closed system. I bought mine from Jegs, one of those billet types and works well. Aside from that, any that was made to come off a performance V8 should be fine.

[BDR561]

I pull around 10" of vacuum showing on the vacuum resevoir gauge, just enough to keep the PB functional (could be better). I don't believe I really have enough to run a traditional PCV w/o loosing more vacuum.

Misting isn't really bad, but I do get a little vapor (when running hard) around the vents as they are vented on the bottom. Is there any vacuum created at the air filter base (I would think much, but how much do you need for the crank case gasses to escape efficiently?).

Would like to have a clean and efficient engine

[mr0077]

I haven't done this test, but I'd bet that if you hooked up a PCV valve (or if you already have one) and check the vacuum during normal idle and then put your thumb over the end of the valve to seal it off, you wouldn't be able to see the difference on your vacuum gage. If that is so, then a PCV valve wouldn't affect your idle vacuum enough to affect your power brakes. I think I'll check that next time I fiddle with my car...

[Bryan Wilson]

read discusions here
Cheers,
Bryan

[BDR561]

If I do the traditional setup, I will have to iether tap the intake for another vacuum source, or put a T-fitting in so the PB and PCV can share the same port.

I will check to see how my vacuum is effected with the PCV.

Thanks for your input

[speed220mph]

A PCV valve is a win-win deal. They allow nasty vapors from being evacuated from the crankcase and burned, plus they keep oil vapors off your engine. The rattling you hear is the valve is shaked back and forth is the valve being moved in the totally closed position for WOT operation to the slightly opened one for idle. It's mostly opened at part throttle.

Installing a PCV valve may require rejetting to a fatter jet if you're running a carburetor(s). Most of the "vapors" pulled from the crankcase is air (O2, Nitrogen, etc.), thus creating a lean condition at part throttle. Others include water vapor, CO2, CO, acid and HC. The best thing to have in a crancase is low pressure (vacuum), which is accomplished with a PCV valve, except at WOT operation. So, unless you're running a race car, it's best to run a PCV system.

[mr0077]

I thought I read that you shouldn't tee the PCV off the brake booster line 'cause it will confuse the PCV and compromise the brake vacuum signal.

[BDR561]

Define race car?

410 Stroker, 12.5:1 C/R
Mighty Demon
Edel Sr. Intake
Solid Rollers
Nasty Cam: .696/.683 lift
Duration @.50 278/286
Lobe 110

Loves to be on the 3000 - 7000+ range...

To PCV valve or Not to PCV valve, that is the question?