I keep mine on a pcv valve with a breather on the other side, I hear/read putting a vacuum on the crankcase actually makes room for a little power, but some say its just a way to foul spark plugs.
Two of my buddies are die hard local 1/8th mile dragsters and they both run two breathers in each valve cover and swear its better but I think it just makes for an oily engine bay after a bit.
Maybe the best bet would be a vacuum pump with an oil separator but on a low reving street car probly a waste.

 

I run a pcv valve on one valve cover and a breather on the other and it doesn't seem to hurt performance at all.

 

I have same arrangement at carcass and joininomader. I can't see how it would hurt any engine and it does tend to limit oil coughing up through the breathers.

 

PVC is for stock or mild high-perf engine JMO. I would run open breathers in your engine.

 

I run breather caps on both covers with hose to carb from one....:tu
Cowboy :flag6:
:gba:
bowtie-trifive

 

Strong vacuum is needed for pcv to work correctly, there is also pcv valves from 60's hipo engines with weaker spring. ..that kind of valve should be used with high perf cam with lower vacuum.
Ron your cam is a little more than "mild" and like said i would use breathers.

 

Mikko, My cam makes 16 inches of mercury for vacuum. I made sure the cam would make enough vacuum to give the brake booster a good signal. So Does that mean i have a mild engine? I hope so with the price of gas what it is over here.

 

Yep, that's mild in my book. I don't think your mileage is "that terrible" after all...your Nomad isnt a prius for sure though...:sign0020:

 

What is the alternative if there is no PCV or Breather? Will it have an adverse effect on your motor?
Larry From Tulare, CA

 

this is a good thread, for i would like to put my M/T Valve Covers on, but there is no way for a PVC. just having a breather on each side, i`m afraid of all that pressure in there for a long trip. years ago, air came "in" the oil fill tube, and "out", of the Down Tube, correct?

 

and, [sorry], the pressure in the engine, is`nt that why these dragg cars have the hose from the valve cover to the collector, to pull the pressure/fumes out of the engine?

 

That's evac system...needs open headers or pipes without any restrictions. Not good for street driven car.

 

I'm running that setup on the street with a blower and headers and was told it was fine it also helps the rings seal.

 

My first 55 had a late 70s era 350, small dome pistons and 4.10 gear. I just had the valve covers capped without vents. I wound that sucker up on the highway and after about 2-3 miles, I heard a loud boom and started smelling oil. The pressure blew the gasket out from under the corner of the valve cover. Lesson learned. I always run PCV valve now but I have probably never had more than a 300-350 horse power engine.

 

What is the alternative if there is no PCV or Breather?

You have to have something, otherwise the pressure will fail your gaskets, and overcome the ring seal.

Just a breather is going to leave an oily mess around the breather.

Probably the best way if you don't want to run PCV (and I would on most) is breathers with hoses connected to a vented, baffled puke tank.

The evac systems that use a whistle in the header collector are only effective at moderate to high rpm.

Some drag race engines use a smog pump converted to a vacuum pump. I've seen them on high performance street engines too.

The ultimate is a dry sump which evacuates both oil and vapor from the engine.

 

since piston rings do not seal 100%

you will have some internal pressure inside the engine.
and it has to go somewhere. ( or you will blow out gaskets or seals)
vents will allow the pressure to escape, along with oily fumes.
a PCV valve will recycle, and burn off the majority of the unburned gases,
eliminating alot of the mess and oil residue.
if you feel it will foul the plugs or cause your engine to burn oil, then maybe your engine is tired and the rings are bad?
I use a PCV on every motor I own, but thats just my choice.

 

I had a major oil use problem with my 396 that I solved.

When I got the car, it was using about 1 qt. of oil in 100 miles and smoking like crazy. The PCV was configured like this in the standard location with no baffle.



I made up a quickie catch bottle to see if the PCV was the source of the oil loss. Well, it would fill up about 1/3 in five miles, so I figured that was it. I added a Mopar style breather/separator and relocated it to the top of the valve cover (drilled out the blank spot provided) to get it away from the oil splash in the valve cover.


I still get a small amount of oil in the jar, but nothing like it was and it uses almost no oil at all now and no longer smokes.


I plan on monitoring it for a while and eventually removing the jar and re-configuring the setup to look better.

If I don't run a PCV, it pukes oil out of the rear main. Normally I would say that the rings are bad and there is an abnormal amount of blowby. But this is a new build and the plugs look great. I had read that Chevy big blocks need a PCV or it will do that regardless. I'm not sure if it's true in every case, but it is in my case anyways...

 

I run a PCV on every motor I work on. I get really anal about the oil vapor smoke look out of the breather. Even with high overlap cams there's usually enough vacuum to keep the 'wispy' look down.

If anybody asked about it I tell them that I'm a "green rodder". LOL

 

Green rodder...that's great! well, I like to max the amount of fresh air/fuel mixture in my induction system...as far as I know, oil mist is only good for detonation...if you can make more power out of it I'm all in :sign0020:

 

Green rodder...that's great! well, I like to max the amount of fresh air/fuel mixture in my induction system...as far as I know, oil mist is only good for detonation...if you can make more power out of it I'm all in

Hi Mikko,
Your points are well understood, and you're right about potential detonation, and also there's probably a tiny power loss.
In the OP's post he did mention "for street cars".

I know guys who run PCV's with no breather at all on the street. The theory being that the vacuum pulls the crankcase to at least even if not to a negative pressure. I tried to explain to them that at upper R's the valve closes, but it fell on deaf ears. I got curious though and tried it myself a couple of times. I didn't notice any difference from my usual way so from then on I went back to my valve plus breather, as it also gave me an oil fill by pulling the breather. I like the oil fill on the drivers side myself.

I had a major oil use problem with my 396 that I solved.

fiftyfive210,
I could be wrong but in your first pic it looks like the placement of the PCV hole might be right over a rocker, at speed it would spit oil right up into the valve. In your 2nd and 3rd pic with your 'test' contraption it's obvious that you drilled out the blank cover hole and plugged the first one. That alone might have helped. There's also the possibility that your valve might have stuck open. I had that prob once myself. It took a while for me to find out that mine was only partially closing.

Also, on an unrelated subject (sorry), your intake looks like a Holley Strip Dominator. I really like them things, but I found through experimentation that my 396 ran FAR better on the street with a good dual plane, even an aluminum GM intake worked way better. I was bummed, but couldn't argue with success. I did find however that the Holley did work good on 468 plus motors. If you get bored sometime try a dual plane on your 396 just for kicks.
Dan

 

55twoten I have ran the Mopar style pcv cap successfully on various types of engines. Usually I run an inline PCV valve instead of the 90° elbow. It seems to work well.

 

From what I understand, the most important job of positive crankcase ventilation is to suck out and burn blow-by gases (some always get past the pistons and rings) to prevent them from contaminating the oil.

However, if you frequently change oil, like in a race car, you don't have to worry so much about oil contamination. In that case, some type of static breather system will work.

 

You should use baffled valve covers with a PCV valve or it will suck the oil right into the engine. I thought I had a bad new motor and it ended up being a PCV valve with MT valve covers with no baffle.

 

Don't know of any reason to have a PVC valve or to have a hose connected from a breather to the air cleaner.. Tossed both when I put the 406 engine in , but kept a breather in each valve cover. Breather hose to air cleaner helps if you are pushing a little oil. You must have breathers otherwise there is a strong possibility of oil leakage, engine needs to be vented. The orginal engine has to vent sources 1. the filler cap 2. road draft tube.

 

I have thought using a pvc on one valve cover and the other one using a puke tank with a breather on top. This is a good topic.

 

hmm lots of different ideas on this one...prompted me to research further, here is what I found:

"correct" pcv system set-up requires a fresh air source as well as the pcv valve, to be as far apart as possible so as the air flows between the two it can be mixed with as much of the contaminated internal air as possible. The vacuum source connected to the pcv then pulls air from the fresh air source (the opposing valve cover with either an open breather or a hose connected to the air cleaner), thru the motor and thru the pcv to be routed back into the manifold. From the posts it seems there is much confusion as to when this happens. My understanding is that at high vacuum (idle or cruise) the valve is nearly closed, coinciding with the low amounts of blowby at idle or cruise. As vacuum decreases coinciding with more throttle and thus more blowby, the valve opens then allowing the contaminated air to be routed back into the manifold. At WOT and very low vacuum, the valve is all the way open, but with little or no vacuum the contaminated gasses escape thru the other breather either to the atmosphere or if connected to the air cleaner they are then sucked in thru there.

If I am correct here I think I will make a compromise, here is my logic...I will use a pcv on one cover since I do want some sort of active way to draw contamination thru and out of the crankcase....but I will not attach the opposing breather cover to the air cleaner, and instead just use an open breather there since at WOT when I'm looking for the most power I will not allow the contamination to enter the air cleaner via that route...of course the PCV will be open, but with little or no vacuum I may not be drawing a large amount thru there. (Ha, with the open breather right next to the air cleaner, I may be sucking it in anyway!..but at least it won't be directly routed to it)

I also learned that the various PCV valves are in fact calibrated to close based on an anticipated amount of vacuum...So it looks like the PCV to use for a low vacuum producing cam is from Year One products part # FP1003, used in LT-1 and L-88 vettes back when those motors were making some power. Again if I'm understanding this correctly, this PCV valve will require less vacuum to stay closed or nearly closed at idle and cruise, thus not giving you essentially a large vacuum leak at idle.

Then one more thing I'm wondering about...Assuming you have a pcv system correctly setup... have the carb manufacturers compensated in their mixture settings based on you having a pcv system in place that will always be introducing additional air into the system?...in other words if you remove the pcv and thus remove air, are your factory Holley, Quick Fuel etc carb jetting and bleeds affected?

some weigh ins needed!

 

I will use a pcv on one cover since I do want some sort of active way to draw contamination thru and out of the crankcase....but I will not attach the opposing breather cover to the air cleaner, and instead just use an open breather there since at WOT when I'm looking for the most power I will not allow the contamination to enter the air cleaner via that route...

That's exactly how I have it and it works well for me.

Again if I'm understanding this correctly, this PCV valve will require less vacuum to stay closed or nearly closed at idle and cruise, thus not giving you essentially a large vacuum leak at idle.

I've always wondered why it doesn't act like a big vacuum leak since its connected to what is essentially an open air source.

 

Yes you have the right plan.

I've also recently seen some ads for a "performance" PCV, but the only thing it can do is act similar to the high performance OEM setups you mentioned.

One thing I've never considered was the difference between a breather on the intake side, vs. connecting to the air cleaner. I suppose that at high rpm, with some blow by, you get some oil vapor back into the intake. I'm not sure whether that's a serious deal or not, but I understand the logic.

 

Everything affects to A/F ratios, I would guess that pcv does too...it is like controlled vacuum leak after all. I was amazed how much difference even air cleaner made to mixtures and mine is really free flowing with big element.
Anybody else see the possible problem when running functional pcv that at high rpm low vacuum situation the crankcase ventilation can be very compromised. I would love to see some high performance boat engine crankcase breather systems and how they work.

 

I've always wondered why it doesn't act like a big vacuum leak since its connected to what is essentially an open air source.

The reason it's not a big leak is pretty straightforward. The hole that the air passes through in the pcv valve is pretty small. That's why it's "controlled".