Ok, I know this may seem like an unusual question; but, does anyone make a PCV valve to use with a performance cam.
When my '92 LT1 was stock, the intake vacuum at idle was about 20".
Now that I have a performance cam, the intake vacuum at idle is about 15".
Since a PCV valve is vacuum sensitive -- it is supposed to be closed at high vacuum (idle), and open at part throttle (off idle). Since the intake vacuum at idle is about 15", does that now mean it is open at idle? Has anyone heard of a PCV valve for a vehicle with a performance cam?

Tom Piper

 

AFAIK, our PCV valves don't have springs in them so as soon as it sees a vacuum signal the little ball should instantly move. I think the only time you wouldn't want the crankcase subject to engine vacuum would be when it's shut off. That way the fumes from the gas tank collect in the evaporative cannister instead of venting thru the intake manifold and into the atmosphere where they can do all sorts of horrible ghastly terrible things to small fury woodland creatures and endangered species.

I believe vacuum is highest at idle and decreases from there. There is very little vacuum at WOT (ideally).

EDIT: I thought I knew what I was talking about but I was wrong! I found this website that explains PCV behavior more clearly. Does anyone have specific info about our PCV valves? I'm going to cut one open tonight and see what I find. If the valve is spring loaded then it would seem that the spring would be sized to work with a certain idle vacuum level. Still, I've never heard of anyone having PCV difficulties because of lower vacuum levels from a cam change.



[Modified by jmr302, 3:00 PM 10/29/2002]

 

A performance cam with longer duration/overlap will always lower your vacuum reading at idle. Unless you're having a problem with your power brakes, don't worry about it. You can always get a vacuum can to help. There's no such thing as a performance PCV valve, and even if there were, it wouldn't change your vacuum reading at idle.

 

I know that it wouldn't change the vacuum reading -- the cam is responsible for that. My point is: normally, the PCV valve is not open at idle. But, in my case, maybe it is.


Tom Piper


[Modified by Tom Piper, 3:19 PM 10/29/2002]

 

Is there such a thing????

If there is give me the part number...and where to buy....

Joke right??????

:eek: :eek: :eek:

 

In any case it is. The pcv valve is supposed to be open as soon as the engine is fired and creates vacuum. If you pull the pcv valve out while the car is running and put your thumb over the bottm end you will feel the plunger close. It is designed to open at a light vacuum # to allow removal of crankcase pressures. It does not matter what cam you have, nor how much vacuum you lost, as long as you still have vacuum it will function ok. They need to be open even at a low vacuum # because as you make a full throttle run you will loose all vacuum at first and then slowly build vacuum as the load decreases/rpm builds, as the rpm increases so does crankcase pressures so the pcv needs to open back up as soon as possible to help offset the pressure building in the crankcase. Now with that said, I used to sell aftermarket parts, and there was a co. making "high perf" pcv valves. They were almost triple the cost of a regular pcv valve, and thier specs were identical to oem replacements! You don't have anything to worry about. :D :cheers: