I know that PCV sucks hydrocarbon fumes out of the motor and burns them.

1. What does the PCV valve do, why not just have an elbow in the valve cover instead of a valve?

2. Why not just cap everything up and not let the hydrocarbons out?

3. Why couldn't you put the PCV valve in the intake manifold above the lifter valley?

4. Has anyone ever seen a PCV valve with barbs on both ends instead of just one, so it didn't have to be sticking out of the valve cover?

The reason I am asking is that I would like some of the gnarly looking GM Performance die cast natural BB valve covers, and I don't want to drill them for PCVs. I had some cheap covers once that didn't have baffles, and they let the PCV suck a quart of oil out every 300 miles. New ones with baffles solved it. But the die cast ones don't have holes so obviously no baffles, and I don't want to start over with that action.

Any suggestions?

The pcv valve is spring loaded and tuned for a particular engine. Manifold vacuum vs spring pressure determines flow rate.

I've never seen one installed via the lifter gallery. If you did try it there you would still want to take the intake through both valve covers in order to get flow through the entire engine. So you would end up with more hoses than the original.

You can probably get an in line pcv if you look around, but it should be a close match to the original.

A pcv system has a number of benefits besides emission control. It removes the blow by that would normally collect inside the engine and eventually be sludge. It will help minimize some oil leaks by maintaining a negative pressure thus less seal leakage under certain conditions.

If your original hookup was to the air cleaner, you're best to keep it that way. If you draw from the engine compartment instead of the air cleaner the velocity will increase on the outlet to the manifold and the higher the velocity the more tendency to carry oil out of the valve cover.

The baffles inside the valve cover are designed to do just that... Decrease the velocity of the exiting air flow by increasing the the free area of the route. The baffle doesn't block the oil, from leaving, it just creates a tunnel with the openings larger than the free area of the exit port (the hose or the size hole in the pcv valve) in effect slowing down the air movement and allowing the oil mist to fall out.

PCV has a spring loaded check valve in it. the checkvalve keeps manifold backfires from igniting fumes in the engine. the spring loaded part shuts off flow to the PCV when manifold vacuum is low. It a controlled vacuum leak, an elbow would be a plain old vacuum leak.

Cap every thing, pressure builds till some gasket or seal blows out. the stuff in the crankcase is gases that escape the rings. sealed crankcase, pressure builds up.

you could put it in the valley, this has been done. there's still the baffle problem. Also, there has to be a fresh air inlet somewhere. you'll notice that most all engines have PCV and air inlet on opposite corners of the engine. That's so vapors are circulated and pulled into the PCV. Without fresh air being circulated moisture builds up and generates the nasty milkshake looking gunk. One of the major by-products of combustion is water in vapor form. it condenses in and engine same as anywhere else. nasty deal if not well ventilated.

there are lots of PCV valves with barbs on both ends.

any way you work it you need a PCV valve that doesn't suck oil and a fresh air inlet. it's nice but not required if the fresh air inlet is filtered air. again, look at the stock Chevy setup works.

Squido types faster....

I know that PCV sucks hydrocarbon fumes out of the motor and burns them.

1. What does the PCV valve do, why not just have an elbow in the valve cover instead of a valve?
Because that would be an uncontrolled vacuum leak. The PCV valve limits total flow; and prevents back-pressure from a backfire in the intake manifold from pressurizing the block.

2. Why not just cap everything up and not let the hydrocarbons out?
Pressure build-up in the crankcase will push oil out the dipstick tube; and can cause oil to be forced past the seals and gaskets. PCV pulls more than hydrocarbons, by the way. Also removes moisture and keeps the oil from turning acidic.

3. Why couldn't you put the PCV valve in the intake manifold above the lifter valley?
Any number of engine families do that; or similar to that. Old smallblocks had the PCV and breather at the front/rear of the engine; sticking them in the valve covers didn't happen until the late '60's or early '70's.

4. Has anyone ever seen a PCV valve with barbs on both ends instead of just one, so it didn't have to be sticking out of the valve cover?
Anything is possible, but no, I haven't seen one like that.

The reason I am asking is that I would like some of the gnarly looking GM Performance die cast natural BB valve covers, and I don't want to drill them for PCVs. I had some cheap covers once that didn't have baffles, and they let the PCV suck a quart of oil out every 300 miles. New ones with baffles solved it. But the die cast ones don't have holes so obviously no baffles, and I don't want to start over with that action.

Any suggestions?
Figure out how to route the PCV front/rear like the old engines? (Good luck, it won't be easy with most intake manifolds. But then, anything is possible if you get creative enough.)

Drill your fancy covers and install baffles?

Drill your fancy covers and install Mopar-style breather/separators?

Drill your fancy covers and install a baffled grommet?

Sell your fancy covers and keep the covers that are already baffled and have proven to work well?

Squido types faster....
So do you.

Schurkey, you must have started later. Nobody types slower than I do. :)

I'm pretty slow myself. Tom would have finished first if I hadn't left out the part about the moisture.

So would a pair of filtered breathers,one one opposite ends of each valve cover do the job?

My engine is a mix of stuff that the previous owner's builder put together. I have a chrome air filter base/lid that didn't have any provisions for the PCV return hose. That hose was always hooked up to one of lines at the base of the carburetor. Could that have been a problem with my amount of vacuum, etc?

I tried baffled PCVs, baffled grommets, etc, and nothing worked until I got my current valve covers that have a big boxy baffle that keeps oil way away from the tip of the PCV. Again, sucking from the base of the carb, maybe I had too much draw from the PCV?

Sounds like for tidiness, I want to keep my vented oil fill lid on one valve cover and the PCV on the other for good cross ventilation....

I had an after market crome pcv to the carb base and was having very low idle vac. 5". I put a 2nd pcv inline and the vac is 10" now and much more tunable and still has a strong suction at the valve cover.

So would a pair of filtered breathers,one one opposite ends of each valve cover do the job?

Would a breather on each valve cover work for him? Or do you need that vacuum draw thru a pcv on one side?

you need the vacuum draw-through across the engine from one side to the other, preferably from one side front to the other side rear.

you need the vacuum draw-through across the engine from one side to the other, preferably from one side front to the other side rear.

So could you connect the two breathers on the valve covers? My carb has no place to hook a vacuum line. :confused:

So could you connect the two breathers on the valve covers? My carb has no place to hook a vacuum line. :confused:
NO. You bought the wrong carb for a street-driven car. You MUST have manifold vacuum (metered by the PCV valve) to draw fresh air into and through the crankcase. The PCV is little more than a "vacuum cleaner" for blowby and condensation that would otherwise contaminate the oil. No vacuum--no vacuum cleaner.

NO street-driven car should be without a PCV system. If you don't have a vacuum port, you may want to break out the drill motor and drill bits; then tap the hole you've created for a pipe-thread hose barb. Or epoxy a short piece of steel tubing into the hole--anything so as to accommodate a 3/8 hose for the PCV valve connection. Some folks drill a carb spacer if there's hood clearance enough to use the spacer. Drill the hole so as to allow the PCV fumes to enter between the throttle blades on the primary side of the carb; you want the fumes to be distributed to both planes of a dual-plane intake manifold so that as much as possible, ALL the cylinders get some of the fumes; and no one cylinder, or group of cylinders has to deal with all the fumes.

OK, 7" vacuum at idle, how in the heck do you pick a PCV valve with the right flow characteristics for that?

Sounds like I will keep the PCV on one side and vented oil filler cap on the other. Ya know, that dumb cap just has steel wool stuffed in it, which would strain out pop cans and leaves at best. Should it actually be one of those little filter looking units to keep things tidy in the engine?

OK, 7" vacuum at idle, how in the heck do you pick a PCV valve with the right flow characteristics for that?
Yup, not easy. I have been totally un-able to find specs for spring tension or flow rates on any PCV valves. The best you can hope for is to select a stock application that has about the same displacement and idle vacuum; and then try the PCV valve listed in the catalog for that engine--and hope it works.

Ya know, that dumb cap just has steel wool stuffed in it, which would strain out pop cans and leaves at best. Should it actually be one of those little filter looking units to keep things tidy in the engine?
I use a GM-style PCV filter--the kind that's called a "Bowtie" filter due to the shape of the thing. Do keep in mind that the steel wool in the breather cap gets oily, and the oil attracts and holds some of the dirt in the air passing through it; it is--sort of--a filter.

I am useing a this, i have not ran the engine yet, so i hope it works correct on my 496 any thoughts?

Is the only purpose of the spring on the check valve in the PVC to resist backfire effects? I guess I am wondering why not just put an elbow on it and let it draw freely.

I called BG and asked about what my new Mighty Demon will want to see as far as flow volumes from a PCV. They said they have never noticed a tuning difference with or without a PCV. But it seems like when I was running with my avenger, if I put my finger on the PCV hole, it would idle differently.

Gibs did you check out my post# 11? Put your vacuum gauge on the base plate of the carb and see what the vac is and how much it changes going to the pcv. Mine was to low and I added a 2nd pcv valve inline and got the vac up to 10" from 5.5" and still have suction in the valve cover

http://i104.photobucket.com/albums/m187/fshrmn_2006/newupload125.jpg

I think that the only BB's that came w/ no-hole valve covers are the old Mark I 348/409/427 "W" engines of old!

So therefore you would need to rig up some sort of second hole in the valley of the block probably in the top rear of the intake in front of the dizzy and then figure out how to add an oil filler tube to the front of the intake manifold!

NOT very practical to me AND I still have my stock no-hole 350SS chrome SB valve covers up on the shelf!

And there's only one 350SS set up like this and it was in '67!

pdq67

aukai, what is that in-line hex shaped metalic thing? The second PCV?

Yes there is one under the breather and the hex is actually a screw in pcv that is 3/8 barb and the threads are about 3/8s also the hole is much smaller than the one in the breather and acts as a restriction and raised my vac at the carb but still maintains suction

Sorry to hijack the thread but I have a pertaining question for my application. I am running a 700hp 500 cubic inch BB with a .700 lift solid roller. The intake is a tunnel ram with two stage I Barry Grants. I bought valve covers with the breather holes in them several years ago. Should I or can I still run a PCV? I have 12:1 compression with little or no vacuum ( i assume). The car will be assembled later this year and this is one of my last plumbing questions. I am wondering if I will run into excessive pressure by not running a PCV valve. I dont want to run a panny vac. Any suggestions?

-jeff

Sorry to hijack the thread but I have a pertaining question for my application. I am running a 700hp 500 cubic inch BB with a .700 lift solid roller. The intake is a tunnel ram with two stage I Barry Grants. I bought valve covers with the breather holes in them several years ago. Should I or can I still run a PCV? I have 12:1 compression with little or no vacuum ( i assume). The car will be assembled later this year and this is one of my last plumbing questions. I am wondering if I will run into excessive pressure by not running a PCV valve. I dont want to run a panny vac. Any suggestions?

-jeff

No, you don't need to run a PCV.

You will, however, need to run breathers, or a pan evac, or a vacuum pump. You need some way to let the blowby gasses escape.

Cars and trucks ran just fine for 60 years without a PCV system on them. They just ran a road draft tube vented directly into the atmosphere. They didn't die, blow up, clog up, stall, or anything else.

The PCV system was just the first of many attempts to limit the amount of combustion by-products dumped directly into the atmosphere.

My 540 runs just fine with breathers in both valve covers and no PCV. The 327 in my Biscayne has been running fine for fifteen years with nothing but a road draft tube.

Vent it and forget it. Unless you're a major tree-hugger.:D


Randy

or unless you don't like that nasty smell. Anybody here old enough to remember what LA smelled like before PCVs were required? Ugh.

Thanks for the input Randy! Greatly appreciated!

-jeff