PCV question... take 2


(this time i wont ask for anyones specific help, since if i mention a name, its assumed to be a private thing, regardless of potential info for everyone...)


1. ive heard a board member talk about tall valve covers effecting the PCV operation. is this due to using improperly baffled covers, or does the volume inside the cover have some effect im not aware of?

2. im planning to run tall, cast alum valve covers that do not have a PCV or breather hole. i will drill a hole and use one of thoes moroso baffled PCV grommets for the drivers cover, and a moroso baffled breather grommet for the pass side. will that cause any probs, or is there a better way to do it?

3. if i bought a vac pump,and i plugged it into a valve cover... should i have a breather on the other side? where should it pump to? if i sent it to a catch can with a breather on it, the can would eventually fill with my engines oil... but how long would that take? and if it fills quickly, is there a way i can automaticly seperate the oil from the bottom of the catch can and drain it back into the pan without having to do it manualy?
i basicly want a slight vacume in the crankcase, with fresh air coming in from a breather/vac valve in the other side valve cover , and all the oil that comes into the catch can i want to drain back into the motor automaticly... how can i do this?

 

The vac pump will come with instructions answering all your questions about installing it.

Basically, for a stock type PCV system to work properly, the system must be sealed. GM's Service Manual specifically addresses this point. That means no breather on the other cover, no leaking gaskets either (intake, oil pan or valve cover).

If you think about it and trace the route of the vacuum in a properly set up PCV system, you will see that adding a breather to the other cover introduces a vacuum leak to the engine.

This is because both heads are connected via the lifter valley and all the blow-by is sucked through the PCV and into the manifold on a TPI system.

My advice; either run two or more breathers and dump the PCV or run the PCV with the second hose to the TB off the passenger side valve cover (which takes care of WOT/low vacuum conditions).

Jake

 

that doesnt help. i dont have any vac pump install instructions

thats dead wrong. the stock setup takes clean filtered air (usually from the air filter housing, air intake, or throttle body) and sucks it in the pass side cover, and all the dirty air is sucked out the drivers side cover...

i know how the stock setup works... sealing off the engine and running only a PCV valve would be stupid.... it would be like running with no vents at all......

and the breathers with no PCV isnt a option for me... i dont like getting oil all over my engine all the time... i like to paint my stuff to look nice... getting oil mist on it when i drive it would suck... esp since i put on 40k+ a year


anyone have any info about the vac pump install info or the effectiveness of the moroso baffled grommets?

 

[QUOTE]Originally posted by JakeJr
[B]The vac pump will come with instructions answering all your questions about installing it.

Try to find the maker's website. Most of them have their instructions free for download. If not, give 'em a call and they can fax or email them to you.

Jake

 

Mr. Dude is right.

Jake is wrong.

With a PCV system, a filtered vent must be used, other wise the sytem will not function properly.

And yes, Jake, they PCV system DOES introduce a vacuum leak. However it is a metered leak (to around 8 CFM at idle) and that is taken into account with carb jetting or ECM programming.

As for the Mr Gasket baffled grommets, I've never used them, so I have no useful comment in that regard, but I did want to back you up about PCV theory.

 

All you need to do is take out you GM book, go to the page with the vacuum routing for the engine and you will see the direction that the vacuum flows.

At WOT the airflow is high through the TB (metered), and this takes over from the PCV which is closed due to the absence of sufficient vacuum to keep the check ball suspended. At idle the PCV does the work and the other hose is, effectively dormant..

Putting a breather on one valve cover while using a PCV on the other introduces a vacuum leak; air that has not been measured by the MAF. Simple.

GM did not design the stock PVC system to function by sucking in un-metered air.

I've seen 1/4 mile and 1/8t mile engines with so much blow-by they blew the breather right off the valve covers. the more miles on the engine the greater the blow-by too.

I just finished building a 434 for a friend's 86 Vette and we went with two breathers on each valve cover and no PCV. If they can't do the job at 7000, we plan to go the vacuum pump route. like the big boys are doing now. But that sucka is pricey.

Jake

 

There's another thread on-going right now on the same topic.

"PCV OR NO PCV; THAT IS THE QUESTION." Lots of good ideas there.

Jake

 

Hmmn,

Gonna have to relook my stock setup...but IIRC, the pass side VC is plumbed directly to the plenum (unfiltered) and the driverside VC had the PCV on it to the plenum....both well after the air is filtered...unless I don't recall beans , as most my age do...ah well....

 

Ah, wait a minute, I see what you're talking abot as "filtered air".....which really is not an issue here, since the PCV and the vent both draw from the VC (unfilitered). i/e the air drawn from the VC is not filtered.

 

I used to hate changing the little white filter on my stock PCV system in my 84 stock q-jetted 305 camaro. that little clip always cut my fingers taking it off...but anyway, my stock PCV system had an inlet filter in the air cleaner housing. led to the passenger side v-cover. this is the general set-up of the PCV system, with the PCV valve on the driver's side, in my engine fundamentals class we were shown that it had to do with the rotation/windage of the crank, with the crank throws spinning that way. why the air inlet? the (bad) air that the PCV sucks out has to come in from somewhere, otherwise it would run out of air to circulate.

 

Right. The concern here is metered/measured airflow, not necessarily whether it's filtered.

Take a TPI setup: we all know that the system requires that all air entering the engine be measured by the MAF. That amount of airflow is one of the factors the ECM uses in determining fuel (injector "on" time) and ignition timing.

So for the calculations to be as close to accurate as the system can get, there must not be any unmetered air introduced into the engine. Otherwise there will be more air introduced into the engine that the MAF has accounted for.

If a breather is installed along with a PCV, unmetered air is introduced into the engine; air that has not been measured by the MAF. The O2 sensor will detect this lean condition send signals to the ECM so indicating. The ECM will then correct for this by increasing injector "on" time.

Speed Density systems have a more difficult time though.

The air/pressure that continues to need venting originates from the amount of air that escapes past the piston rings as the engine is running.

Dennis Wells said he's seen so much pressure build in an engine's crankcase that the oil pan actually ballooned with the engine running on his engine dyno.

Jake

 

THINK DAMMIT!




if the air is taken from the thottle body (where its already been measured), and this is the only air inlet in you sealed engine (it should be) and the air leaving there goes into the motor.....

the only unmesured air is upon startup. just like the air in the plenum.

ITS ALREADY MEASURED! DO A SEARCH! READ! THINK! and stop arguing over **** that doesnt matter in my thread!

i couldent give a crap less about how TPI wants it... im trying to make a efficent system to take the crap air out of my motor, seperate the oil back into the pan, and burn the rest.

from the point you said use one PCV valve and or just breathers, you havent impressed me with your crank case vent knowlage...

 

Now, now now. Let's all try to be adults here. Reasonable people can disagree without all the emotion, right?

Jake

 

MrDude,

1. I doubt that the height of the rocker covers will affect the operation of the PCV system. The design of or lack of baffles may have a greater effect.

2. You can drill your holes for the PCV and clean air supply wherever you want. Just check for clearancee first, adn locating them on opposite sides shuold be most effective.

3. Where is the vacuum pump going to exhaust its air? Your querstion seems hypothetical, since you asked "IF I bought a vac pump..." Do you have a pump now, or are you only contemplating getting one?

 

I agree with the height issue; the height of the cover won't cause a problem.

The only point I would make is that if you look at the rocker arrangement on the SBC you'll see that there are two locations on each head which have the largest separation between rockers .

These are the ideal locations to drill the hole(s) since holes drilled there will not be directly above the rocker, and we all know how much oil gets squirted from the rockers.

If the holes are drilled above any of the rockers you can expect increased oil flooding of either the PCV or the breather.

Just my thoughts.

Jake

 

contemplating getting one. but i dont want to have to drain the oil in the catch can on a regular basis on my street car. i realize im making my car a lil wild for a street car, and i know that means more work on the car, but i know me, and i know that eventually, i will forget to manualy drain that can... i want to know if i can do it automaticly.




also, has ANYONE else tried the moroso baffled grommets?

 

Yes they work fine, same basic design fNord has used for years but they get more crud buildup then a standard chevy baffle.

 

cool. thanks.