Chevy Nova Forum banner

1 - 20 of 35 Posts

·
Registered
Joined
·
2,261 Posts
Discussion Starter #1
Is a PCV valve absolutely necessary? I have valve covers with one breather hole in each. I can either use two really nice, open element K&N breathers or am wondering if one of the covers needs a PCV valve. If so, whats the best routing setup? Should I drill a new hole for the PCV and still use two breathers, one on each side?

I recall my old setup had a v/c hole on the rear drivers side with a pcv valve that ran to my brake booster. It was always hooked up like that and that's how I left it. I am not sure if is is mandatory or ideal to have a pcv valve hooked up to vacuum somehow to actually suck vapors or will the breathers alone be ok.....thanks
 

·
Registered
Joined
·
4,760 Posts
well i run a pan-e-vac system on mine. i use to run two k&n filters but they would still spray down my valve covers :yes:
 

·
Registered
Joined
·
577 Posts
You can't go wrong with a pcv and breather on a street driven car. If it was an all out race motor I could see the use of a pan-e-vac or similar setup, but i could not justify the added cost or complexity on a driver as they perform the same function and are probably just as effective. There is good reason that manufacturers have used this setup for decades...it works.

The pcv gets connected to manifold vaccum which is the large front port on an edelbrock or the large rear port on a holley.

Dan
 

·
Registered
Joined
·
438 Posts
A pcv valve really isn't required on a non-emissions controlled engine. A lot people like to remove them because they tend to suck up a little oil and it either gets deposited in the intake or gets burned in combustion, this is one reason you don't see them on drag cars. There are many cars on the road with no pcv valve, it won't hurt a thing.
 

·
Premium Member
Joined
·
4,125 Posts
You need something to properly scavenge the crankcase. The PCV is the simplest and most efficient. Run it.
 

·
Registered
Joined
·
3,601 Posts
Do you NEED it? No. Do you want it? Yes. While I'm not a fan of most smog devices, PCV will keep your oil cleaner and make the engine less likely to leak oil. Do not tie it into you power brake line it will reduce the signal to the booster. You want the pcv hooked to a source thats as ballanced as possible, Preferably the plenum, not an individual intake runner.
 

·
Premium Member
Joined
·
7,732 Posts
A pcv valve really isn't required on a non-emissions controlled engine. A lot people like to remove them because they tend to suck up a little oil and it either gets deposited in the intake or gets burned in combustion, this is one reason you don't see them on drag cars. There are many cars on the road with no pcv valve, it won't hurt a thing.
Not true. Just running breathers on the valve covers is a big mistake. A PCV valve really shouldn't be looked at as an emissions device. The main purpose of a PCV valve is to evacuate the harmful blow-by gasses from the crankcase and to apply a negative pressure to help seal the rings and gaskets. It just happens to also reduce emissions at the same time.

Every engine ever made all the way back to the 1920s has had some type of crankcase evacuation system. When the cylinder fires, an explosion occurs in the combustion chamber that forces the piston downward. Some of the gasses from the explosion inevitably leak past the rings and go into the crankcase - even with brand-new engines. This is called blow-by. Of course as engines get older and wear, they tend to allow more blow-by.

Blow-by gasses are acidic and contaminate the oil and corrode the internals of the engine if not properly evacuated by some means. The constant pressure from the gasses also causes the rings not to seat properly and the gaskets to leak. In the old days, engines had a draft tube attached to the back of the block that hung down towards the road. As the car moved, the tube acted as a venturi which created a negative pressure and helped draw the blow-by gasses out of the engine. There was also a breather on the top side to draw fresh air into the crankcase as the vacuum sucked out the blow-by. Back in the old days there was always a black streak in each lane of the road from the draft tubes sucking out the blow-by and puking it on the road.

In the 60s, car companies started to use PCV (Positive Crankcase Ventilation). It used the vacuum created by the engine to draw-out the blow-by gasses. This not only worked better than the draft tubes (especially at idle), it also reduced emissions by re-burning the blow-by instead of puking it out all over the road and into the atmosphere. The re-burning of the blow-by gasses has little to no effect on performance.

There are two types of PCV systems - open and closed. An open system has an open breather, either on a valve cover or on a tube in the intake on early 60s engines. A closed system (which is still used today), the fresh air is drawn through the air cleaner rather than an open breather. This further reduces emissions.

The best set-up for a performance street application is to have an open system with one breather on one valve cover and the PCV in the other connected to a manifold vacuum source. It can be connected to the same fitting on the intake manifold as the power brakes. You do not want a breather in the same valve cover as the PCV valve or it will only evacuate the one valve cover and not the entire crankcase. A simple set-up that will not affect performance yet will protect your engine.

Race engines tend to spend a lot of time at WOT where they produce very low vacuum signals. A PCV valve won't do much in this situation. That's when they start using belt-driven vacuum pumps and draft tubes in the headers for a crankcase evacuation system.

The bottom-line is that every engine needs some form of crankcase evacuation system whether it be a PCV valve or some other means. Just running breathers in the valve covers is the biggest mistake you can make. They will not do the job adequately.

Engines without PCV or crankcase evacuation are shorter-lived and will eventually (sooner than later) burn and leak oil and turn into oil-burning pigs. Crop-dusters. If you don't run PCV, your oil will become contaminated by the blow-by gasses and quickly turn black as coal. You will also start to see oil leaks from the positive pressure. You basically cut the life of your engine at least in half.

If you use PCV, your oil will stay golden longer and your rings and gaskets will seal better. You'll have more power and a much longer-lived engine.

That's why PCV shouldn't be looked at as just an emissions device. It's an essential component to the performance of any engine that just so happens to also reduce emissions. You should frequently change your PCV valve. A good rule of thumb is to look at it as part of a tune-up and change it when you change plugs. They don't last forever and eventually the "pintle" inside becomes clogged and they won't work as good as they should. If you start seeing your dipstick being forced upward or oil and crud around the breather, that's a good indication that your PCV valve isn't working right. The "shake" test that guys use to listen for rattling does not work. A PCV valve can still rattle and yet not be at 100%.

Install a PCV valve. Your engine will thank you for it by being around a lot longer.
 

·
Premium Member
Joined
·
8,405 Posts
Yeah, I agree. The PCV is an important, beneficial system. I think of it as performance enhancement on an engine much like crankcase evacuation systems.

Some combustion pressure leaks past the rings and pressurizes the crankcase. Piston bottoms have to push against the air in the crankcase. Fighting this air pressure adds to pumping losses (negative torque). A Positive Crankcase Ventilation system brings the pressure back down to ambient or maybe a little below.

Some Hot rodders are adding an inline oil separator, pressure regulators and taken it to a new level.
 

·
Registered
Joined
·
1,286 Posts
A pcv system works great untill the vacume falls to nothing at wide open throttle/high rpms- then you'll puke some oil out the breathers and push the dipstick out depending on how bad the ring seal is and if they flutter up high.
Many people are using a pcv system + an exhaust type pan evac system for the best of both worlds.
 

·
Premium Member
Joined
·
2,102 Posts
That's why if you spend the majority of your time at a low vacuum situation you run a vacuum pump to keep negative pressure in the crankcase. Now on a street engine, my opinion is that you want a frsh air intake on the system, so I like the PCV in one and a breather in the other. Or, how I'm changing mine, I'll run a breather in each valve cover and the PCV in the intake, but I run a Victor JR. that'll allow me to do this easily.
 

·
Registered
Joined
·
2,541 Posts
or you can get a Moroso crankcase evaction kit that plumbs from your valve cover breathers to your header collector and out the exhaust it goes... it also helps your piston rings seal better too......
 

·
Registered
Joined
·
2,541 Posts
What about this? Anybody ran this kind of evacuation system? It isn't a PCV valve, but not sure what to call it (perhaps an exhaust evac system). I will be running this very soon as I only have two breathers.

http://summitracing.com/parts/MOR-25900

Is this better than a PCV setup?
yes, thatts the kit im talking about. and yes its better than a PVC because it sucks more out of the crankcase...
 

·
Premium Member
Joined
·
8,405 Posts
A pcv system works great untill the vacume falls to nothing at wide open throttle/high rpms- then you'll puke some oil out the breathers and push the dipstick out depending on how bad the ring seal is and if they flutter up high.
Many people are using a pcv system + an exhaust type pan evac system for the best of both worlds.
PCV isn't like vacuum advance which relies on vacuum to work.

Do a little experiment. Run a hose from the intake manifold to the inside of your car and do a wide open throttle run. Put your thumb over the hose and feel the suction at wide open throttle.
An engine is an air pump and even (especially) at WOT, it's is moving air into and through the engine. If it didn't, the engine wouldn't run.

Each cylinder generates low pressure and when the intake valve opens, air moves into the cylinder. The crankcase has higher pressure than the intake at WOT/high rpm because of blowby. This pressure will flow into the intake manifold and be consumed by the engine.

While it sounds plausible that PCV will stop flowing air when intake vacuum goes to zero but it doesn't...unless something is wrong.

If your engine is over-pressurizing the crankcase and pushing out the dipstick then you simply have too much blow by overwhelming the PCV. Instead of band aids to ventilate the excess blow by you'll be better off fixing the root problem of poor ring seal.
 

·
Registered
Joined
·
2,261 Posts
Discussion Starter #17
Some really good replies here. Thanks a lot.

I think I will be fine with my current setup which has an open breather on the left front cover and a pcv grommet (need to get the valve, no biggie) on the right rear cover. Cool, I don't have to buy another breather. Not much but it all adds up. That hole in the rear of the cover is a short and easy run to a fitting I can install near the plenum, kind of on the #8 intake runner of the manifold. Or, I can always go the carb if need be but I think I will run the pcv to the manifold then my brake booster to the big port at the back of the carb. And I guess with this setup, I can add/install oil simply through either hole in the covers. Sound good?
 

·
Premium Member
Joined
·
4,125 Posts
Some really good replies here. Thanks a lot.

I think I will be fine with my current setup which has an open breather on the left front cover and a pcv grommet (need to get the valve, no biggie) on the right rear cover. Cool, I don't have to buy another breather. Not much but it all adds up. That hole in the rear of the cover is a short and easy run to a fitting I can install near the plenum, kind of on the #8 intake runner of the manifold. Or, I can always go the carb if need be but I think I will run the pcv to the manifold then my brake booster to the big port at the back of the carb. And I guess with this setup, I can add/install oil simply through either hole in the covers. Sound good?
I'd do it the other way around. At least that's what the factory did.
 

·
Registered
Joined
·
2,261 Posts
Discussion Starter #19
I'd do it the other way around. At least that's what the factory did.
Not a problem. I can run the PCV to back of carb and brake booster to fitting off rear manifold. better?

I did read in another recent thread that pouring oil into v/c BAFFLE is not a good idea. Both my covers have built in baffles. Hmmmm, gonna have to find an easy way to add oil, maybe add a hole and cap to one of the covers...???
 

·
Premium Member
Joined
·
4,125 Posts
Hmmmm.... I add mine through the breather hole and haven't noticed any issues.
 
1 - 20 of 35 Posts
Top