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Old 05-30-2008, 04:37 PM   #1 (permalink)
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PCV System on 302

Ok I have the PCV valve from large vacuum port on carb base to passenger valve cover. Driver valve cover has Breather / Filler. Pulling 14" vacuum in park. Whats happening is Im getting oil out the breather. Why?
Yes, PCV is good. AFR185 heads. Am I missing something?
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Old 05-30-2008, 05:08 PM   #2 (permalink)
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Re: PCV System on 302

At wide open if the carb is the right size, there won't be much vacuum. What valve covers are you using, do they have baffles. Oil is flying all over in there. If not MR Gasket makes a insert for the breather tube. It's like a check valve-baffle to keep the oil in. Works and under 10 bucks for 2.
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Old 05-30-2008, 05:48 PM   #3 (permalink)
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Re: PCV System on 302

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Originally Posted by TIGERFOMOCO View Post
At wide open if the carb is the right size, there won't be much vacuum. What valve covers are you using, do they have baffles. Oil is flying all over in there. If not MR Gasket makes a insert for the breather tube. It's like a check valve-baffle to keep the oil in. Works and under 10 bucks for 2.
I agree. Another thing is the wrong size PCV valve or an engine with too much blowbuy.
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Old 05-30-2008, 05:55 PM   #4 (permalink)
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Re: PCV System on 302

I agree needs baffles.
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Old 05-30-2008, 06:07 PM   #5 (permalink)
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Re: PCV System on 302

The valve covers are Ford Motorsports Tall Aluminum with baffles on both sides. Its a 3/8" PCV line.
I will check on the extension.
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Last edited by chas319; 05-30-2008 at 06:09 PM.
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Old 05-30-2008, 07:40 PM   #6 (permalink)
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Re: PCV System on 302

does this only happen after high RPM pulls? check your PCV valve, it may be sticking. i had a similar problem, mine even tested okay, but after i replaced the valve oil stopped blowing out of the breather.

Last edited by PaceFever79; 05-30-2008 at 07:42 PM.
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Old 05-30-2008, 08:19 PM   #7 (permalink)
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Re: PCV System on 302

The baffles on those valve covers are still pretty open on the ends...I am having the same troubles..
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Old 05-30-2008, 09:19 PM   #8 (permalink)
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Re: PCV System on 302

The pcv valve is open when there is vacuum. When you are wide open or nearly wide open (lots of load), there should be no vacuum...which means that the PCV closes. Then where does the crankcase pressure go? Yep...out the breather. That's why you get oil in there.

Most PCV systems use a valve in one valve cover which goes to vacuum. When under light load and high vacuum, the vapors are drawn into the air intake and burned. On the other end, there is normally a hose that runs from the air box or air cleaner. The air cleaner will normally be under a slight vacuum (not a lot but there will always be a little pressure drop) when under wide open throttle. This pressure differential betwen the crankcase and the air box/cleaner will cause the vapors to be pulled into the air cleaner and burned. Take a look at most OEM setups to see what I am talking about. The factory designed them pretty good...well...unless you have a F150 Lightning (2nd generation).

Also, if you have a breather on one side, make sure it has a filter. It can and will pull lots of dirt into the crankcase.
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Old 05-31-2008, 03:50 PM   #9 (permalink)
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Re: PCV System on 302

CarCraft magazine did an article about this exact same thing a few months ago on their "Street Sweeper" Chevelle. They found these nifty clamps that seal the breathers to the valve covers so there is absolutely no oil blowing out from underneath them. The clamps cost a good bit (like around $60 a piece), but it sure looked good.
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Old 05-31-2008, 05:26 PM   #10 (permalink)
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Re: PCV System on 302

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Originally Posted by mavman View Post
well...unless you have a F150 Lightning (2nd generation).

I know what your talking about! I had an '01, with 14lbs or bootst. I miss it badly.

-mike
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Old 05-31-2008, 05:31 PM   #11 (permalink)
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Re: PCV System on 302

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Originally Posted by mavman View Post
The pcv valve is open when there is vacuum. When you are wide open or nearly wide open (lots of load), there should be no vacuum...which means that the PCV closes. Then where does the crankcase pressure go? Yep...out the breather. That's why you get oil in there.
When vacuum is not present at the PCV valve, is when the valve flows the most to the outside. The valve only closes when theres a positive pressure from the intake to the crankcase (backfire or boost)..... and it doesn't perform well as a "check valve" under boost conditions..... as I have confirmed .

Anywho!..... here is a diagram of the PCV flow characteristics under the different vacuum conditions......

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Old 05-31-2008, 08:47 PM   #12 (permalink)
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Re: PCV System on 302

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When vacuum is not present at the PCV valve, is when the valve flows the most to the outside.
If the PCV valve is sticking shut, gummed up, or too small, it can act like a plug at high RPM and not allow the pressure to escape into the tube (as a passive breather) forcing too much pressure to escape out the breather side. I figured this out by experimenting with replacing the PCV valve with a second breather on my engine and it stopped my engine from blowing oil out of the breathers. I then realized my PCV valve was creating back pressure so I replaced it with a new larger valve. It fixed my problem.

Not to say that is what's going on here?
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Old 06-01-2008, 12:51 AM   #13 (permalink)
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Re: PCV System on 302

I have the same problem with a little K&N breather, if i swap it with the Ford Motosport chromed breather (with holes on the bottom), no leaks...

I saw, some steel mesh in the Ford one, the K&N one is empty.
Should i fill it with the same mesh?
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Old 06-01-2008, 01:28 AM   #14 (permalink)
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Re: PCV System on 302

Quote:
Originally Posted by Joel50 View Post

When vacuum is not present at the PCV valve, is when the valve flows the most to the outside. The valve only closes when theres a positive pressure from the intake to the crankcase (backfire or boost)..... and it doesn't perform well as a "check valve" under boost conditions..... as I have confirmed .

Anywho!..... here is a diagram of the PCV flow characteristics under the different vacuum conditions......

Boy I am glad someone brought this subject to light. Proper operation of the PCV valve.

And yes, there are different flow rate valves. Buy a quality valve and not a CHI-COM blister pack at PEP BOYS.
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Old 06-01-2008, 11:13 AM   #15 (permalink)
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Re: PCV System on 302

Ok so I will get a new PCV valve see what that does. The breather is a push on style with holes under the top with filter media in it.
It happens just at idle as I can see. The bad part is that the oil then runs down to my plug boot then to my header. SMOKE!
If that dont work I will pull the valve cover and see what I can make and reply on my findings.
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