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Old 03-13-2012, 01:29 PM   #1
Ak. Mal
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Location: Kansas City, MO ...I'd like to go fishing and catch a fishstick. That'd be convenient. - Mitch Hedberg
Default Oil filler cap, breathers or pcv valve?

When purchased, my car came with a set of valve covers with two holes in each cover. I ended up with an assortment of an oil filler cap, breathers and a pcv valve. (I know, bad idea but I'm fixing it now) I'm buying new valve covers soon with one hole in each cover.

Which parts (cover, cap, pcv) should I be using on the valve covers for my engine? If it matters the car has a 350 with cast iron heads, Edelbrock intake and carb, headers and no smog. I do have the charcoal canister, which could stay or go depending if I need it.
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Old 03-13-2012, 02:03 PM   #2
MelWff
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On mine the driver side has the oil filler cap and the PCV. The passenger side has a fresh air tube connected to the air cleaner. On your 80 the set up might be slightly different.
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Old 03-13-2012, 02:42 PM   #3
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It doesn't really matter which side has what as long as the PCV valve is not on the same valve cover as the breather.

I placed mine where it made filler access and routing of plumbing the easiest and cleanest.
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Old 03-13-2012, 03:52 PM   #4
Ak. Mal
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Is this acceptable?

For the passenger side: http://www.summitracing.com/parts/EDL-4403/

For the drivers side in place of the pcv valve: http://www.summitracing.com/parts/EDL-4413/
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Old 03-13-2012, 04:25 PM   #5
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acceptable for what purpose? Thought you wanted a functional PCV. Why did you select two different types, the second one has nipple for a connection? Do these fit all valve covers or only Edelbrock?
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Old 03-14-2012, 09:25 AM   #6
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I assume they are universal, but I'm buying a set of black Edelbrock valve covers. (http://www.summitracing.com/parts/EDL-4443/) I asked about the breather with the nipple in place of the pcv valve because they don't sell the pcv valves with the breather case over them in black at Summit. A pcv valve allows air to flow out of the crank case but shuts if the air tries to move the other direction. A breather allows air out, but filters any trying to get in.

Would a breather with a nipple be an acceptable substitute for a pcv valve?
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Old 03-14-2012, 09:45 AM   #7
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for a proper operating and functional PCV system you need both an input side for fresh air to come in and an output side for the crankcase vapors to excape. These should be on operate sides of the system so the air flowing thru the systems actually flows THRU the crankcase to force the vapors out.
You need to have a breather on one side (one valve cover) to allow in fresh air and the PCV valve on the other side (other valve cover) to allow the vapors out.
If the valve covers yo are using do not have an oil baffle on the insde to keep oil from coming thru the PCV valve you can also get a baffle gromment from Moroso
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Old 03-14-2012, 09:53 AM   #8
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Quote:
Originally Posted by Ak. Mal View Post

Would a breather with a nipple be an acceptable substitute for a pcv valve?
No. You need negative crankcase pressure. Prior to pcv systems (or on an L88)) they used a road draft tube to create that neg prssure. If you use just a breather you should have a road draft tube .

You want a pcv valve and, if you must, a breather. The oe design flowed the replacement air from the bottom of the air cleaner so that it went through the paper element air filter first. Those after market breathers flow the air through a wad of steel wool. It'll keep the flies out of the crankcase, but won't do much for dust and grit.

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Old 03-14-2012, 09:59 AM   #9
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I have a question about the pcv also. Is this for pollution purposes or is there a reason a breather on both sides would be a bad idea. I understand that the crank case needs to breath but is there any benefit to sucking it out as apposed to just being vented?
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Old 03-14-2012, 10:09 AM   #10
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Here's how the stock system works
Click the image to open in full size.
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Old 03-14-2012, 10:14 AM   #11
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Quote:
Originally Posted by Steve2147 View Post
No. You need negative crankcase pressure. Prior to pcv systems (or on an L88)) they used a road draft tube to create that neg prssure. If you use just a breather you should have a road draft tube .

You want a pcv valve and, if you must, a breather. The oe design flowed the replacement air from the bottom of the air cleaner so that it went through the paper element air filter first. Those after market breathers flow the air through a wad of steel wool. It'll keep the flies out of the crankcase, but won't do much for dust and grit.

Steve g
Only the open element (IE LT-1 style) drop base air cleaners drew air from within the actual air filter element. All closed style filters had a tube from one valve cover to the air filter housing but only had a little cheesy filter that clipped to the inside of the housing (outside of the actual engine air filter).
The push in style breathers are just fine and have worked for decades.

Just pick a decent breather filter that actually has a filter element. Not sure where the 'steel wool' ones come from but I haven't seen them in years (but I don't buy the $2 Cal-Custom ones either).
The real fancy ones are made of the same material as your intake's air filter element.

Bottom line is you need a working PCV valve in one cover and a decent breather in the other.
Elm
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Old 03-14-2012, 10:20 AM   #12
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I understand the basic principal of the pcv, I was more curious about on a high performance engine. Would you decrease performance by sucking in crankcase gases with your clean air and fuel. Did they put this system on cars for pollution puposes only or is there other reasons?
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Old 03-14-2012, 10:24 AM   #13
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Quote:
Originally Posted by GT's 78 View Post
I have a question about the pcv also. Is this for pollution purposes or is there a reason a breather on both sides would be a bad idea. I understand that the crank case needs to breath but is there any benefit to sucking it out as apposed to just being vented?
Both-
PCV Valve is an emissions device but also a damn good idea.
Venting combustion blow-by into the atmosphere is not only irresponsible but it doesn't benefit you over a PCV valve.

Without the PCV, you don't have forced fresh air circulation inside the crankcase. This circulation is what helps keep the motor cleaner inside and helps your oil to last longer. Without a PCV, if your blow-by is high enough, all you'll do is to manage to spew oil out of your breathers and make a mess of the engine compartment. This is just a bad idea all around.

Don't try to out-think the engineers- A PCV valve is one of the emissions devices that is actually a good idea from both and engine and environmental standpoint.
KEEP IT!
Elm
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Old 03-14-2012, 10:24 AM   #14
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There is no "negative pressure" [vacuum] inside the engine block. It builds pressure. The purpose of the 'road draft' tube was to vent it to the atmosphere. Effective for relieving the pressure and fumes, but nasty for the environment.

The PCV system allows the engine to vent via the valve, once it builds to a small level of pressure (defined by the spring and valve mass in the valve assembly). When it vents, it discharges pressure and vapors to the base of the carburetor, where they are burned with the fuel charge. So that a vacuum can't be created, the opposite valve cover has an air intake that is connected to the air cleaner housing. If any vapors were to be discharged from that intake, the engine would also get them via incoming induction air.

So, if you want a working PCV system...which costs nothing in terms of engine performance and keeps your engine compartment from gumming up with oil vapor residue...you need a PCV valve installed in one valve cover, an air inlet tube/hose installed in the other valve cover and run up to the air cleaner housing, and an oil filler hole and cap/plug somewhere in either valve cover. There should be a baffle inside the cover, under the PCV valve hole, so that rocker arm oil splash won't get directly sucked up by the PCV valve. Otherwise, your oil will be slowly lost and burned by the engine.

If you want to keep the fuel vapor recovery system (a good idea, IMO), install a 3/8" T-fitting at the outlet of the PCV valve; run the vapor canister 'purge' line to one of the upper T fittings and an outlet hose from the other T-fitting to the large fitting on the base of the carb. You will also need to run a smaller vacuum hose from a "ported" (or "timed") carb fitting to the vacuum switch on the vapor canister so that it will function only when the engine has some throttle applied [not operating at idle]. You do not need a 'breather' if you set it up like this.

Last edited by 7T1vette; 03-14-2012 at 10:28 AM.
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Old 03-14-2012, 10:27 AM   #15
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Quote:
Originally Posted by GT's 78 View Post
I understand the basic principal of the pcv, I was more curious about on a high performance engine. Would you decrease performance by sucking in crankcase gases with your clean air and fuel. Did they put this system on cars for pollution puposes only or is there other reasons?
Primary driver was emissions control-
If anyone can prove a performance difference in any street car running no PCV vs having one, I'd be the first that wants to see this data.
Elm
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Old 03-14-2012, 10:31 AM   #16
Ak. Mal
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So what I really want is the breather with the nipple connected to the base of the air cleaner on the passenger side and a pcv valve on the drivers side tee'd into the carb and canister?

What would be the difference if I put a breather on the pass. side and the nipple breather on the driver side and hooked the pcv hoses to the nipple? The crankcase would still be vented and the pcv circuit would still exist, just not with a pressure operated valve. What about adding a nipple breather on the passenger side and hooking it to the air cleaner assembly?

Last edited by Ak. Mal; 03-14-2012 at 10:39 AM.
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Old 03-14-2012, 10:31 AM   #17
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[QUOTE=7T1vette;1580276135]There is no "negative pressure" [vacuum] inside the engine block. It builds pressure. The purpose of the 'road draft' tube was to vent it to the atmosphere.


There is neg pressure in the crankcase with a working pcv. It is not engine vacuum, but it is a neg pressure. The pcv should draw more air then the engine bypasses. Worn out engines will exceed the pcv capacity and you will get pos pressure and would see wetness on the breather end. Hold a piece of paper over the breather side of things. That's how you were to test a working system. That's the design,the pcv is intended to negate any pressure that would build in the system.

Road draft tubes are designed for just that. The air moving over the end of the tube as the vehicle moved created suction. Hence the name "road draft" and not "vent".

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Old 03-14-2012, 10:31 AM   #18
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Thanks guy's
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Old 03-14-2012, 10:32 AM   #19
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You definitely want a functional PCV system as shown in post #10 (with exception a breather would be ok in place of drawing air from the air cleaner). Your engine will last longer. Every drag car I've ever seen (that didn't look like a hack job) had a functional PCV system. Some even buy those little electric motors to help suck out the air instead of going through the engine. But that cost money.
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Old 03-14-2012, 10:36 AM   #20
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On the carb, is the pcv connected to ported or manifold vacuum?
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Old 03-14-2012, 10:36 AM
 
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