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Old 02-02-2012, 01:10 PM
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Number of PCV's

Only because it seemed like this was as good a place to ask this question, as any, and because it was everything you ever wanted to know about PCV's, but afraid to ask....
I've gathered that I should run my (1) PCV valve on the driver's side, being fed vacuum from the base of my Edelbrock 600CFM carburetor. So far, NO PROBLEM.
MY Question: Is there any advantage to running TWO (2) PCV valves (one on each valve cover) or would you advise AGAINST running two (2) PCV's?
Both, of course, piped into a vacuum source from the base of the carburetor, to burn off crankcase fumes? Thanks GUYS! GREAT Thread!

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Old 02-02-2012, 01:39 PM
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How MANY PCV valves should I use?

I've gathered that I should run my (1) PCV valve on the driver's side, being fed vacuum from the base of my Edelbrock 600CFM carburetor. So far, NO PROBLEM.
MY Question: Is there any advantage to running TWO (2) PCV valves (one on each valve cover) or would you advise AGAINST running two (2) PCV's?
Both, of course, piped into a vacuum source from the base of the carburetor, to burn off crankcase fumes?
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Old 02-02-2012, 01:48 PM
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Think of it like this. A fire is built in a steam locomotive so it's air entry is only on one end. The PCV works one in the same, vacuum is pulling it from one side of the engine. On the other side is a vent that pulls in air while the valve is working at low RPM high vacuum. At wide open throttle where there is no vacuum the vents role reverses and the blow by exits out of the vent since there's no vacuum to pull in the blow by.
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Old 02-02-2012, 02:15 PM
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Dont run 2! you would lose too much vacuum more then one!! One is fine and its good for 5 hp as apposed to running none! If you want more crank case ventilation put extra breathers on your valve covers is one way

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Old 02-02-2012, 02:21 PM
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You are right, the passenger's side doesn't have it's own breather.
The passenger's side valve cover only has one opening for a metal elbow, or possibly a 2nd PCV valve. The driver's side valve cover has a small opening, especially for the PCV valve and a second larger opening for a breather / oil cap.
I guess my question should read: Rather than using just a metal elbow, (being fed to the base of the carb) would a 2nd PCV valve be of any added value?

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Old 02-02-2012, 02:25 PM
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The passenger's side valve cover only has one opening for a metal elbow, or possibly a 2nd PCV valve. The driver's side valve cover has a small opening, especially for the PCV valve and a second larger opening for a breather / oil cap.
I guess my question should read: Rather than using just a metal elbow, (being fed to the base of the carb) would a 2nd PCV valve be of any added value?

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Old 02-02-2012, 02:30 PM
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Do NOT use 2 PCVs, one on each valve cover......The "V" in PCV stands for ventilation.....If you have 2 PCVs with no vent, you are just going to end up sucking oil out of the engine into the carb. If you are sucking air out, you need to put the same amount of air in.
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Old 02-02-2012, 02:38 PM
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So, poncho62 is saying, "Don't use a 2nd PCV valve on the passenger's side valve cover, but rather the factory's metal elbow, which also feeds into the base of the carb., for continuous vacuuming of fumes (and possibly oil).
The passenger's side has GOT to use one, or the other. The metal elbow was installed at the factory, had a rubber hose attached, which then fed into the base of the carb.
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Old 02-02-2012, 02:53 PM
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What I am saying is that you cant suck air out of the crankcase without putting an equal amount of air in.....That elbow is supposed to have a rubber hose attached which goes up to the air cleaner to get that air.

If you just have PCVs on both sides, its like putting a vacuum cleaner on your hand........it sucks until its got nothing to suck.......and there goes your oil
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Old 02-02-2012, 03:12 PM
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Tim, you have the same question in two separate threads, please don't double post, see the Board Guidelines. I've merged them here. Thanks.
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Old 02-02-2012, 03:18 PM
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This is one thing that GM has spent a lot of trial and error on.

After multipe different arrangements, the best setup by far is the PCV in the forward end of the left (driver side) valve cover, & the breather end (or tube to the air cleaner) on the aft end of the passenger valve cover.

This is how you want to do it. Inlet on the passenger side (air sucks in), exit on the driver side (fumes sucked out by engine vacuum & injested into the engine thru the PCV valve).

Since the PCV vavle is a one-way check valve, running 2 wont work.

Last edited by tjet; 02-02-2012 at 03:27 PM.
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Old 02-02-2012, 03:58 PM
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One more thing to add - since the PCV system uses engine vacuum, it's basically a vacuum leak. So engineers needed to factor that in on carb & ignition design and tuning.

So, the factory PCV system is calibrated. Any changes to the system will effect the calibration. The valve itself may not operate properly if the system is drastically changed.

It flat out works. No need to reinvent the wheel here
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Old 02-02-2012, 08:38 PM
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Just thought I would add my 2 cents worth.
Earlier car engines used to be directly vented into the atmosphere through the breather on the valve covers or through a breather tube,sometimes there was a vacumm created in the cranckase (on decceleration) thus the engine ingested unfiltered(dirty) air upon acceleration or as the engine wore the fumes were vented into atmosphere.
Pollution laws changed all this,the pvc was added to create somewhat of a contolled vaccum in the cranckase,this did several things.
1 It prevented the fumes from escaping into the atmosphere thus reducing the amount of oil fumes
2 Reduced the amount of oil leaking out of the engine(instead of oil leking out,air would be sucked in)
When the amount of negative pressure inside the engine exeeds the resistance of flow of the breather then air goes inside the engine through the breather,but the "best" air to be induced into the engine is of course clesn air,thats why a lot of brathers are plumbed through the engine air inlet,the pcv valve plays a balanced role in all this "dance" and is engineered to maintain preset parameters of negative pressure,adding another one would be of no practical use and would serve no purpose other than unbalacing the A/F mixture.
I hope this answers ur question
Short version....dont do it motor will run worse and u wont gain a thing...
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Old 03-15-2012, 08:16 AM
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Thanks to everyone who posted a reply. I now understand that only ONE (1) PCV valve should be used, the the driver's side valve cover, in the front hole, (using a grommet). After watching a video posted by Edelbrock, the vacuum-port to be used (for the PCV) is on the front of their 600CFM carburetor, on the larger, (lower) driver's side vacuum port, which is a constant manifold vacuum. I was running the hose to the back (center) of the carburetor, to get vacuum. I've installed a screw-in breather on the driver's side, oil-fill screw-in location. Is that breather okay, or does it kill the cross-ventilation from the passenger's side valve-cover vent that run into the base of the air cleaner? I can only hope this question makes sense and doesn't portray me as a total idiot.
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Old 03-15-2012, 01:09 PM
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WOW.......put the pcv on one valve cover and the breather on the other valve cover.....done!
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