Should your crank case be AIR TIGHT??

[Dr. Righteous]

I noticed some black spooge at the front right corner of my valley pan on my 383. There is a small gap where I am getting some blowby when I romp down on the gas.
Of course my vacuum goes to near 0 and there is no PCV action. Also, without PCV any pressure in the crankcase will cause the rings not to seal as well leading to more blowby. All this made me ponder some of the dynamics of PCV and how much air should be let in and how much is too much. The PCV is stright vacuum from the manifold. Is the crankcase suppose to be 100% air tight accept for the breather on the valve cover? Is the breather restricted only to let a small amount of air in? How much is too much and when do you know there is something wrong?

[ehostler]

The PCV is supposed to close, when you romp on the pedal. The lack of PCV action is not causing blowby. Blowby is caused by ring gap on the pistons.

You should have a small breather on one valve cover and the PCV valve on the other.

If you are getting excessive blowby during hard acceleration, it is time for a rebuild, as your rings aren't sealing as well as they should. A compression and/or leak down test should tell you how your rings are doing.

[Dr. Righteous]

Nope. The engine is fresh. Everything measured and built to spec for the KB pistons. It has close to 10:1 compression. The question is when your manifold vacuum is 0 at WOT how is the crankcase evacuated?

[blackcuda]

That is the problem with the pcv system, it works when you are cruzin around town but at WOT the zero vacuum does nothing! That's why many race cars use the crankcase evacuation system, but it doesn't work as good as the pcv at idle/ part throttle. The other alternative is to run a vacuum pump. They work all the time, but cost mega $. I did see a guy at the track a few weeks back that made one for his 66 rust-stang. He said he made it from parts that he got from work and it cost him under $40.00! When I see him again I will try and find out what he used and how we might could fit one on one of our cars. I'll post it when I get him to talk.

[70gtx]

my thought on this is when at wot the other breather that is usually hooked to the air cleaner should be able to handle the blow by.sometime you will see them run to the outside and not to air cleaner ,by a hose run beside motor to the ground. it sounds like you have to much blow by if you do have a pvc on oneside and a breather on the other and still have problems.

[ehostler]

If you have a breather with a hose that runs to the air cleaner, make sure that you have the filter element for it. I have seen a few that didn't have the element. They tend to have oil all over the inside of the air cleaner.

The PCV is to suck the blowby out of the crankcase, so that it doesn't sit around and break down the oil. As WOT is not for extreme periods of time, vacuum begins to pull it back out, before it can do much damage. The breather on the other valve cover allows it to vent, untill vacuum is restored, to pull all of it out.

[Dr. Righteous]

I was just thinking that a air cleaner tube to the breather would probably solve this problem, but I have Edelbrock Signature Series valve covers and air cleaner and there isn't any prevision for this. Hmm, I will have to think of a solution.

[Rug_Trucker]

Did you put a new breather on the engine? They can plug up. They allow air into the engine. My old 440 was not set up right. NO BREATHER! After a while when you romped on it it would blow oil out of the front of the engine. I had to pull the cast iron sixpak off (read very heavy) and do a new valley pan and add a breather. problem solved.

[Dr. Righteous]

It has a new Edelbrock 'signiture series' chrome breather in the oil fill hole. I pulled it off and was eyeballing it yesterday. there is a small flap that could be opened more with some screwdriver bending. I think I will have to pull the intake and valley pan off also and fix the leak. Also my heads were shaved .020". It made the intake difficult to bolt up. If I have it shaved too it should bolt on better.

[ehostler]

When you had the heads shave, you should have had them shave the intake side as well.

If you have the intake shaved to mate to the heads, that intake will only work with those heads. If you have the heads shaved, any intak will work with it.

[mopar_man]

YOu say you have a new engine built to spec? Do you have a windage tray?
You could be using the wrong viscosity oil which can foam and vaporize under high rpm.
i would also dabble with the timing, blow-by is sometimes increased when your engine is too far advanced on timing.
hpe it helps

[HOLESHOT]

Dr. R,try this,ensure you have a sufficent size breather or if necessary 2 on the valve cover opposite PCV.If the hose is soggy to PCV replace it,next is the cam idle vaccum lower than stock?If so is the PCV a stock PCV for the stock383?If so look in the parts book for one from a HP 383/440 that had a lower vaccum signal, are they the same part # as yours.Next what kind of oil,did you go snythetic 5x30 as suggested or do you still have that heavy glue in your engine..?Is the PCV shielded in the valve cover from oil splash that will contaminate cylinder charge and the hose integrety.The better we can control blow by and internal windage the better the rings seal which includes the kind of oil and its oil additive package,also consider 1/4-1/2 qt less oil in the pan and see if this helps.

[Dr. Righteous]

I am still running 10w-30 regular oil. I'm waiting on a couple things before I changer over. (replacing oil pan)
It does have the MP windage tray and there are baffles shielding the PCV. The PCV valve is a stock 383 valve and my idle vacuum is about 15 inches. What I am going to try is opening up the 'flap' on the breather cap. It looks like it was made to pry open further if you needed more venting. It may solve my problem. I will keep everyone posted.