im going to put a breather on my passenger side valve cover to clear up the engine compartment. my question is the tube that was originally there, where it plugs into the throttle body, how do you cover that off. Is there vacuum from that point? i guess you would cap it right?, anybody know what to cap it with what size it is and how to seal it properly?
Thanks

 

You have an 89. By installing a breather in place of that tube, you'll be introducing a vacuum leak to the car. The air supplied to the PVC system on a MAF car needs to go through the MAF first in order to be accounted for.

 

i want to put it on the opposite side of the pcv where the hose goes from the valve cover to the throttle body. the maf never sees it because the maf is earlier,(correct).

 

Jim85IROC...can i do that on my 91' SD? Can i do it on both sides?

 

I did it on mine.

I have the PCV on one side and a breather on the other side. Been like that for over 3 years and it still runs like a champ.

 

Incorrect. The PCV system draws air from the throttle body though this tube. This air that the PCV system draws gets sucked right into the intake manifold. That's why the system is designed to supply that air DOWNSTREAM from the MAF.

Your 91 is speed density. It does not directly measure the air going into the motor, so running a breather in place of the line from the TB will work fine. Running a breather on the other side instead of PCV won't cause any problems with how the car runs, but it could cause oil to start leaking out of all the various engine gaskets down the road.

 

ok now im confused. the tube on the driver side cover sucks air from the crankcase into the manifold correct.....and the hole on the passenger side is for escaping gas that goes through the throttle body to combine with regular airflow. (if that made any sense) this is my understanding of it. if im wrong by all means correct me. im not planning on taking off the pcv only the other tube which i thought had no vaccum only fed to mix with tb air..

 

yea, you can pop a breather on the cover and just cover the port.

that is how most SBCs are anyway.


as long as you still have the PCV valve on the other side connected you will be fine

 

alright so if i did this in my tpi, returning to my original question what size is the connector on the tb and what can i use to cap it.

(also on the passenger side does air get sucked out of the crankcase or pushed in, sucked out right) so wait does that mean ill have less blowby being pulled out because the tb vacuum wont be there or will exhaust gases exit as needed?does it matter?

thanks

 

in addition to my post above this ....is it really possible to blow seals because the blowby cant exit quick enough through the breather.....is it just me or does this sound a little extreme?

 

you can either unscrew the connector and put a plug in it, or just put a vac cap over it... honestly, since i dont have one infront of me, i dont recall what the fitting looks like... just plug or cap it with a vac cap.



and yea, that can be true if you're spinning your race motor to 7k+, or if you are running at 6k for extended peroids or somthing........ but most small block chevys since the 70s have had a breather/a PCV setup and they do fine.

if you're worried about it, get a good sized breather that breathes all around instead of a lil chrome dealie that only breathes from the underside....

 

??
From the throttle body the line goes to the PCV valve. Leave that intact.
From the valve cleaner to air filter there is a piece of pipe, that you can remove and install an air filter there.

You want the air to enter one valve cover, and be drawn out the other. that way you continually vent the crankcase and min the build up of acidic fumes, and min condensation. The throttle body supplies the suction to operate the system

In a MAF system the PCV system is a metered vac leak.
On a MAP system it's just accounted for in the MAP air consumption calculation.

HTH

 

Now I am wondering if my setup is correct. Tell me what you all think. I have a filtered breather on the pass. side valve cover. On the driver side valve cover is a PCV valve and hose going into the upper plenum.

After reading the above posts I am second guessing what I have done...

Would an incorrect PCV cause a little oil leak at the oil pan at higher RPMs???

 

ok bye the sound of things we have lots of people in here with lots of different setups . as far as mine goes my pcv goes from drivers vc to intake manifold and on passengers side to the tb. i dont know about anyone elses setup. i did recently look at my haynes manual though. heres a question how does air get sucked from inside the passenger valve cover to getting sucked out the driver side vc??

 

I believe what these two valves is to create positive crankcase vacuum. By doing this you will get less blow by through the piston rings and seals and actually help horsepower. I know a measured vacuum is desired. Im not so sure if removing the vacuum from the throttle body would create a lack of desired vacuum.

 

You know how the manifold is sucking air from the crank case? Where do you think the air in the crank case that's getting sucked into the manifold comes from? It comes from that other tube!

It's one big loop. The air gets sucked into the throttle body through the MAF. It travels down that tube you want to remove and into the crankcase, at which point it's sucked into the intake manifold and mixes with all of the rest of the air on its way to the combustion chamber.

If you remove the tube you're talking about, instead of going through the MAF, it comes from your breather. That means that unmeasured air is getting sucked into the crankcase and on into the intake manifold. That's called a vacuum leak, and if enough air is sucked in that the MAF doesn't know about, it'll make you run lean.

 

That's because most small block chevys since the 70s didn't have a MAF system. No car with a mass air sensor has ever come stock with a breather.

Come to think of it, neither have carbed cars since the 60s. Any stock vehicle since the beginning of the smog era has always run a tube from the air cleaner assembly.

 

At higher RPMs there is very little engine vacuum.
So the PCV valve doesn't open.

As the engine gets older there is more and more blow by, this causes the various seals and gaskets to fail, well amongst other factors. In with this is that if the crankcase doesn't breath well then pressure can actually develope in the crankcase.

And if the blowby is great enough, oil fumes can be drawn thru the PCV system, and oil has a VERY low octane and can further mess things up due to detonation.

The orfice size, and weight of the slug inside the PCV are calibrated items.

 

ok jim now im starting to understand what your saying , the breather air will be unmetered and unmetered air is equivalent to a vacuum leak. alright so ill keep the breather tube so it takes a way measured air, thanks

 

you're right

i should modify that to say, most performance and modified SBCs....

and i get what yer saying with the MAF thing.... but in a SD car that would work no prob.... *shrug*

 

It is metered, that's why there are so many different ones. The size of the orfice and weight of the slug inside, are accounted for in the calibration weither carb or EFI.

 

Hrm. Perhaps i should take off my breather and put that line back on then. I've been running for 6 months without a breather and it has never run lean. I couldn't find a 90* elbow that fits the hole in the valve covers i have, so i just got a breather and put it on. The car actually runs rich , but that has something to do with other stuff. If i remember correctly the vap cap needed was 3/8".

 

well, if you're tuning the car, you can probly tune it pretty well with it on there