PCV breather hooks to...?

[BrandOmatic]

Yep, another newblet question, but i bought a pcv breather for the passenger side valve cover, just wondering where it hooks to? Do I run a line to the carb somewhere, or the air cleaner somehow?

[fasrnur]

Usally on the back of the carb,low on the carb flange is a larger nipple that the hose connects to. At least on the Q-Jet.



Jeff.....

[spacecadet]

The PCV should have a vac tube running to the base of the carb. You should have at least 1 pvc on one valve cover and 1 fresh air inlet on the other cover. The fresh air hole in the other cover could be a vented oil fill cap. Or a tube that runs to the air cleaner to get air that has already been filtered and clean.

If you did tuneing without a pcv, you will have to make adjusments after you install the new pcv.

[Terrybneal]

To spacecadet.what would happen if ya dont have a vented breather on one side of the engine.What if ya only had a oil cap that was not vented?. I have been having some issues with my engine and wonder if it would make that much difference

[fasrnur]

I believe you need to have fresh air drawn in to make up for the vac* created by the pcv. I could be all wet here though. LOL



Jeff....

[BrandOmatic]

alright well i think i got the right parts on in the right places. Just curious how a motor would run with just 2 open breathers? No positive crankcase ventilation, it would just be vented with no vacuum back in... heard that wouldn\'t be good but just wondering for sure.

[Scotty_S-15]

OK, my 2 cents... I think everybody is saying the same thing, I\'ll try to summarize.

........ Two valve covers. One gets a PCV valve and is plumbed to the carb base, where it sees constant manifold vacuum. It sucks air/fumes out of crankcase. Other valve cover opening now has a vacuum caused by the air leaving the other valve cover into the carb/manifold. So you can put on a vented cap, or an adapter to plumb it to air cleaner, where only nice filtered air will enter the crankcase.

........... Regarding Brandomatic\'s thought of dumping the PCV, yeah, not a problem, long as you\'ve got plenty of vents. BUT, the PCV ain\'t really a bad thing, especially if you\'ve got an engine that\'ll see a lot of miles. BECAUSE, the PCV system does MAJORLY keep the crankcase clean. Sucking out all those nasty fumes, water, & acid vapors. I\'ve you\'ve ever torn down 10 year old engine from the early 60s, (pre PVC) vs. a later engine, a huge difference. Some older engines actually had sludge you needed to scoop out. Got me wondering, when did PCV come into play? I\'m thinking mid 60s......

[mzoomora]

I personaly dont like the breather in the air cleaner because it is pulling air through the breather rather than letting it pull air into the engine. It is placed so close to the air cleaner, it cant work against it, thats why those old style breather filters were always dirty. Also, a pcv also sucks out the lost compression from the engine, and they all lose some. If there were no pcv and you had a sealed crankcase the pressure would build up and you would lose ring seal, also the pistn would have to work against the positive pressure in the crankcase which would also cause a power loss.

[Scotty_S-15]

Usually when a breather (air intake for the crankcase) is really dirty and oily, that usually is a good indication that the PCV valve is stuck, or that the engine is tired http://www.s10v8.com/images/smilies/icon_frown.gif and the blowby is getting out of hand. The blowby is creating more positive pressure in the crankcase than the PCV handle. So the excess pressure goes back out thru the intake breather, or if it\'s plumbed to the air filter, up to the PCV filter, oliling everything up, and in really bad cases, even mucks up the air filter.

[BrandOmatic]

OK There is one large nipple on the back of my 750 holley... however.... i thought that was the hookup for the kickdown vacuum signal for the transmission..

[mzoomora]

The large nipple in the base is for the PCV (should be 3/8\"). I usually run the brakes off of the manifold, and the trans off of a smaller full manifold vacuum port.

[spacecadet]

On 2004-07-10 01:48, Terrybneal wrote:

To spacecadet.what would happen if ya dont have a vented breather on one side of the engine.What if ya only had a oil cap that was not vented?. I have been having some issues with my engine and wonder if it would make that much difference





The crank case pressure from \'blow by\' would over pressurize the crank case and blow out the weakest gasket on the engine. Usually the intake gasket between the block and the intake. (most comman that I have seen.) All engines have some blow by. Its also possible that the vacune would suck a gasket in and leak either.





The large nipple on the back of the carb is usually for the vacume for the brakes. There shold also be one on the front. If threse not two than us a spot on the intake.