pcv or not pcv

Hi ,

while on my way to do some paint job on the valve cover, for some reason i have to move the car with the valve cover of. I plug the PCV valve to make sure the engine won t die from to much vacuum leak just to find out that the engine run better with the PCV valve plugged .
Better idle, better Neutral to Drive and RPM drop when engaging Drive.
i have never been able to achieve a proper tuning of my 200 with 250-2v head since installed about a year ago.
It was horrible to drive cold (i m leaving in a tropical area so cold does not mean really cold) and RPM commonly drop 4 to 500 when put in drive.
I have seen quiet a few 6cyl engine without PCV and a wonder if can may be live without it as it seems to improve drivability.
I have read open crankcase vent (without PVC, with breather) will reduce airflow on valve cover and engine and increase temp in general specially in timing chain compartment.
what is you opinion.


regards

Hi,

I have try to find info about this on the internet. it seems to be a really "hot" subject on many forum with a lots of Pro and Cons, and a lots of arguing about that matter.
I wonder if it s the reason why I haven't received any answer.

Well, While waiting for answers, i have drilled a hole on my air filter base to accommodate a NATO (AN) fitting. I have plug the PCV valve here and the engine is running much more smoother. Drive and reverse is no engaging smoothly as well and the engine do not tend to die or to run horrible any more. I can now get a lower idle on drive (500-600 rmp) and therefore a lower idle in Neutral (900 or so) witch is a lot of satisfaction.

Before that engine was horrible when cold, doesn't matter the choke was on, off or anywhere in between. Situation was a bit better when hot.

I am aware depression at air filter might not be high enough to evacuate oil vapor at idle. I guess i would be good enough when crusing at moderate throttle with engine sucking more air. The baffle on the valve cover should prevent sucking oil (specially with very limited depression at the air filter.

I have a similar system on my Suzuky vitara (carb) except the engine does not have PCV valve at all and there is a T connector between valve cover and air filter allowing a really small diameter tube to return to the intake. I would have expected oil fumes to be entierly routed to the intake manifold with such a system but there was evidence of little oil condensation in the air filter case. I guess the system is built that way to maintain good sucking action in both idle and open throttle situation. I might modify my system that way and seen how it behave. the really small diameter tube going to theintake should not create a massive air leak like the larger PVC tube did.

thanks for opinion .

regards

Hi dawnovsky, I always used a PCV on any street car (since the late 1960's) it helps keep the engine cleaner inside. Yes a PCV system will change the idle RPM it's a controlled vacuum leak that draws crankcase combustion gases back into the engine intake. When tuned correctly IMOP there would be no loss of power or drivability. As to it running better without have you done any plug reading before to see if you were jetted correctly?

hi
thansk for your answer.
Well i might be over jetted as well ...
As i don't even know what type of jets i have on my stock 350 holley there s not much reason for them to be properly tuned for the application.
I don't know anything about jet sizing .

PCV valves are sized for specific engines. Make sure you have a PCV valve for the 170 motor. PCV valves can flow to much or to little if the application is wrong, causing driveability problems. I agree with Bubba, motors have never been so clean inside since Positive Crankcase Ventilation system were mandated. Good Luckhttp

can the tube size can have an influence on my rough idle condition ?
I came to use a large tube mainly because this was the closet size i have around.
it is a bit wider than the nipple port of the carb so i need to use a clamp to keep it tight.
May be a smaller diameter tube will restrict the air flow and allow better performance.
One interesting thing is i 'm using the same PCV and tube i have before swapping the head for the 2V
Your are sugesting using a PCV for 170 CI engine as my engine is a 200. Is this one flowing less air than the one appropriate for the 200?
I have found V100 for fairlane 170 CID, but it is a thread type. the v181 is also available but means best suited for 200.
do you know where i can find one ?
i guess it surely worth the effort and money to guve it a try with a new PCV and a smaller tube.

regards

dawnovsky":287ki4rv said:

can the tube size can have an influence on my rough idle condition ?
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Click to expand...

Not so much the tube but the valve its self. I believe that is where the leak is "controlled" If it is for a bigger engine it will be (a bigger vacuum leak or flow) than what is needed and the idle smoothness will be worse. too small and it won't flow enough to get all blow-by gases and moisture from the crankcase.

And think about this, a older engine that has more blow by will have less idle vacuum to start with. so a 1 inch loss is more noticeable.

MY BAD. Use the 200 PCV valve and get the proper hose size, to match the valve and the carburetor. I would try a new PCV VALVE. It is not un common for the spring inside to break or loose tension. Carbon build up can also cause the valve to stick open and loose its seal. . If you still have a rough idle, it is time to look for vacuum leaks. The PCV valve is usually plugged into a grommet in the valve cover, with the other end to the base of the carburetor. The oil filter cap should be vented if this is a open system.