CiCiC3

I have heard it keeps the opposite bank running cleaner using a PCV? I have also seen it with a hose connected to the fuel line feeding into the carb. Ideally it should run to the bottom of the air-cleaner?

Alan 71

Hi ccc3,
When gasoline engine emissions began to become an issue because of concern for the environment, Chevy had 2 systems on their engines.
The 'pvc' generally in the left side valve cover connected by a hose to a port low on the carburetor so it was a vacuum system.
There was also the crankcase breather in the right side valve cover that was connected to the air cleaner base inside of the air cleaner filter.
I guess it depends on what you're trying to accomplish as to what the set-up on your engine could/should be.
Regards,
Alan

The right side pvc connection.






The right side crankcase breather and hose.

CiCiC3

Thanks Alan 71, I would like to do something environmentally good but it's probably a lost cause with my 74 BB. I just want mainly to keep it from getting gunked-up internally. Right now I only have a breather cap on the right side and would like to put a PVC on the left like you have in the picture. Thanks for the nice pics!

ddawson

It's not bank dependent. One side can have a breather or run to the air cleaner.

The idea is that as air is pulled into the valve cover it's filtered air. The air than works it's way though the crank to the other side and back up the other side were the PCV valve is.

Without one you tend to get milkshake build up from condensation.

Alan 71

Hi ccc,
I believe your 74 had a vapor recovery system for the gas tank too.
It's the coffee can looking 'canister' mounted to the rear of the drivers-side front wheel apron.
A large and small hose from that canister travel up to the pvc, and then on to the carb. You can see the hoses in the photos.
You may or may not have that canister in operation and it may be something you don't want to be concerned with at this point.
Regards,
Alan

ddawson

Can create stuff like this.

BKbroiler

Hey Alan, its PCV not PVC. (positive crankcase ventilation)

corvetero

I saw that canister on my 74 yesterday. At the botton of the canister I saw the pigtail where the hose is connected but no hose at all. May be because my carburetor is a Holley 4160 instead the Rochester one?

bluedawg

It's best to have a vacuum on the crank case and in some cases adds power to a modified engine. Alot of folks don't like to to suck the Un burnt and burn gasses into the the induction system as it can lead to predetonation and in some cases if your pcv system doesn't have baffles or a catch can you can suck oil into the induction system. There's 3 ways to avoid sucking the crank case gasses into the induction system, 1) header evacuation system using the header to draw a vacuum on the pcv, this system is relatively cheap and effective providing you don't have a restrictive exhaust. 2) the vacuum pump, bolts on the front of the engine, works best, can run vacuum accessories along with pulling a vacuum on the crank case, fairly expensive. 3) run breathers, allows the engine to breath but does not pull a vacuum. I personally for the time being run the pcv to the base plate of the carb, i have scotch Brite pad filling the baffle so that I can't suck oil up which can happen at high rpm, on the passenger side I have a blanking gromette with 3 each .125" holes drilled in the grommet to allow a tiny bit of air to move trough, but wouldn't be like a vaccum leak and a breather stuck in the hole.

terry82

when I changed my air cleaner on my 82,i put a breather cap in the hole that was for the line that went to the air cleaner.i drove the car for a few years that way.I just put a pvc in that hole and teed it into the exiting one.The engine vac improved,no more gas smell and the cars idle came down a bit.

BLUE1972

The pipe that went to the air cleaner was the vent for the engines PCV system. It was to keep dirt out of the system and feed any "burp" back into the intake to be burned. The PCV system is considered a closed system and should not have any gas smell.

If you have 2 PCV valves and no vent you can damage an engine seal by pulling too much vacuum on the crankcase. there is no air getting into the system. The reduced idle speed is kind of like pitting your finger over the PCV valve - reduced air flow into the engine.

The problem today is that most PCV valves are generic and pull / flow the incorrect amount causing lean or uneven fuel curves in the engine.

PCV was actually a good thing as it kept the crankcase clean of vapors and helped reduce crank case pressure - reduced oil getting forced past the rings.

terry82

when I put the pedal down hard.Then let off .I would get a raw fuel smell ,in the open side window .Now after I give it gas nothing,no smell.The motor seems to like the two pcv .

MelWff

The gas smell is probably from you evap system charcoal canister. What you did to the PCV system makes no sense if you fully understand how the system is designed to work. You should read up on it, below is one of many sites explaining it.

http://auto.howstuffworks.com/positi...ion-system.htm

terry82

well it might not make any sense but ,I don't get the fuel smell anymore.I don't know If its right or not .I know that so far it has worked out well.

MelWff

gee wont you be surprised if the fuel vapors are being sucked into the crankcase, really think you should get a better understanding of the source of the fuel smell and how a pcv system works before you have something unexpected happen. Good luck.

terry82

I don't know where the fuel smell was coming from.i have checked the evap canister.when I changed from the push in breather to the pcv it was because it had so much vacuume that I wondered if that was causing a vac leak.When I put the valve in, the car ran fine and the smell went away.I did read the article that you posted and I see what they are saying .But my car runs good and the smell went away.Thankyou for your help

cooper9811

My .02c cents - When I bought my 79, the PO had installed a PCV on each bank. When I tore the motor down, it had some god-awful black carbon-like build up. Not just carbon in the combustion chambers, I mean in the lifter valleys and all over the interior of the block.

The motor was the original block and had about 60K miles on it.

I won't say this is 100% due to a bad PCV setup - but it clearly was not venting gases as it should have. I have no doubt that contributed to the mess I had to clean up.

bluedawg

That's odd, it seems like if you had a vaccum on both sides when gasses came from cylinders it would dusipate, but given that the only flow would be from the Gas as it enters the crank case from the custom Chamber, theoretically, there could always be combustion gas present in the crank case, with no flow except from the cylinders there would be no pressure, negative pressure even, but with no fresh air to take its place the burnt gas might just linger( kinda like a bong with no carb...haha, but serious). The gaskets seal enough to keep oil in and probably hold a vac. Just a guess, interestingly odd though.

gungatim

the PCV is a check valve, there is a steel ball in there, you can see/hear it rattle. if you have two of them installed, it won't let fresh air into the system and will simply pull a vacuum. proper way is fresh air (filtered) in one side, vapor/moisture out the other. you either burn them through the carb/intake vacuum, or vent to atmosphere by using an external pump of some sort. using the latter is more important on DI engines than our old school motors...

BLUE1972

If you look at some of the seals on you motor you can see that they are designed for holding FLUIDS in not AIR out. Too much Vacuum can cause dirt and air to get past the seals causing abnormal wear.

The piston rings do dot seal 100%. With very high vacuum in the crankcase you will suck unburnt gas and burnt gas vapors past the rings also causing abnormal or accelerated wear of the rings and bore.

A vent on the PCV - valve cover will work as long as it has a filter. It's not ideal butter than no vent.

Gas smell under hard acceleration - actually when you slow down ( the fuel sloshes) is usually from improper / bad gas line fittings , bad float levels, bad floats, bad float seal or a leaking accelerator pump. The only other time I found a car with the smell was after the motor twisted from the torque the fuel line would leak a few drops. I did not want to take into account poor carb gasket or manifold gaskets, but could be a cause.

The PCV system is oil ( vapor and contaminates in the oil system) and Vacuum, no gas involved.

Since you said the motor slowed down to a better idle - you have an air leak somewhere - I'm guessing the carb or manifold.

Good luck with the motor - hope it works out for you.