Thread: pcv really needed?

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I know some guy who has some nice aluminum breathers that will look good on my covers.
They don't have the one with the nipple on it that I guess you connect to the back of the carb, I think that is the pcv.

Do I really need that, these breathers are nice and I want to get them.

You should strongly consider some way of using a PCV valve to get rid of the positive crankcase pressure. If you don't use one, you're likely to be blowing a nice, oily mist out of those nice aluminum breathers on top of your shiny engine.

I wouldn't reccomend it either! Because without a pcv it builds lots of pressure and it has to go somewhere!

I agree ,I have seen gaskets fail when a pcv valve was removed and no breathers were installed, and an oily mess when breathers were used without a pcv valve.

so is the pcv considered a breather with the tube attached to it? Does each valve cover need one with the tube.
Most of the breather sets I see have one breather with the nipple on it and the other is plain, does that do the job?
Can normal breathers be modified to do this if I drill a hole in the side or something and attach a hose fitting?

The thing is, I bought some nice cast aluminum covers off some guy, he had drilled 2 holes in EACH cover for breathers, so I need two pairs for them.
Should I press in a cap to fill one on each cover, or use them both?

Use one set of holes for the PCV, the other for breathers.
Many years ago(I wasa 16 I think) I aquired a beautiful set of ribbed cast aluminum valve covers for a 318 I built for a 67 Charger. I spent a month polishing and detailing the valve covers and they looked great. The VCs did not have place for PCV and I didn't have breather caps, just tight fitting oil fill caps. On my first test drive on the new engine I made it about 5 miles when massive amounts of smoke started coming out from under the hood. Needless to say I about messed my pants. I checked under the hood and everything was covered in oil, the dipstick was about halfway out of its tube but I couldn't see anythign else wrong. I checked the oil, added a little and headed back for home only to have the same thing happen again.
Basically the crankcase pressure built up and the only place it could go was out the dipstick tube spraying oil all over everything. What a mess. I didn't want to drill the valve covers so I ended up getting a breather cap with provisions for a PCV valve which solved my problem. I miss that car

I guess some lessons must be learned the hard way

Bobbyt

ok, I'll find a way to modify one of these so that I can screw in a hose fitting and connect it to the back of the carb.
thanks

My question is, doesn't the PCV dragging air through the block effectively create a vacuum leak at the base of the carb? Am I missing something here...

It seems to be a vac leak occuring at the inlet breather hole.

Andy.

DennyW: This is very interesting to me and you certainly helped me understand how the PCV valve works. Thanks!

I have one of the aluminum, breather/PCV combos on one valve cover and a breather-only on the other. I didn't realize they had variable spring rates on PCV valves. I thought all were created equal. I have had too much cam (and thus not enough vacuum) on a multi-port injection unit and just installed a Comp 276 to help solve that problem. I noticed small amounts of oil in the intake runners and seeping out the vacuum ports when I would disconnect them. Any idea how to help solve this? I have figured it had something to do with "lack of ventilation" but didn't know how to resolve it without causing other problems. Can I measure how much resistance the PCV valve has and know if it is enough?

Thanks in advance...

I have a tech question about a motor i built. It is a pontiac 400 bored 030 over keith black single eyebrow pistons, eagle h rods, comp cam magnum .480 lift cam, comp cam roller rockers, 670 heads w/mild port work, edelbrock performer rpm intake, holley 770 street avenger carb. The problem i have is when i attach the pcv valve to the carb pcv port , the car burns oil like crazy. So I thought maybe i was getting blow by because the rings are'nt seated yet. Did a compression check and all was fine. I then welded a short nipple on the underneith of the air cleaner plate and attached the pcv hose there. Now i get oil blow by out the rear crank seal due to high crankcase pressure. The engine now has about 1500 miles on it with no change. i am using a stock pcv valve , do i need a differant pcv valve. It seems like the exhaust under heavy acceleration is burning quite a bit of oil. thanks

denny, i also thought that the rings were'nt seated but when i removed the pcv line from the vacumn port and tied it directly to the under side of the air filter plate, it quit burning oil all together. it then started leeking oil out of the rear crank seal. does this still sound like ring problems to you. thanks for responding

Denny, did you find the listing for the PCV valves yet? I just completed hooking up a PCV system on my 509 BB Chevy that includes 2 breathers and one PCV valve which is hooked up to the back of the carb. I'm having the same problem, which is some oil is getting pulled up through the PCV valve hose on the back of the carb. My vaccum reading at idle is 6 - 8 psi. I am using aluminum breathers one having the PCV in it.