PCV - technical differences
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Lead Driver
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From: Sheffield, AL
PCV - technical differences
Say you are replacing PCV valves and are asked: less than 8500# or greater than 8500#.
Given that the engine size is the same, what is different? I assume it is flow [controlled vacuum], but is it greater for the heavier application?
Just curious.
Given that the engine size is the same, what is different? I assume it is flow [controlled vacuum], but is it greater for the heavier application?
Just curious.
Post Fiend
Joined: Jul 2004
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From: Northern California
The difference is the spring inside the PCV valve. The spring is weaker or stronger and the PCV valve wont open as much with the stronger spring. You really do need to get the right PCV valve for the calibration of the vehicle, even if the valve looks the same.
As for vacuum flow, I do not know which is greater. You could look at both valves, side by side and see which opening is open more, I suppose with the same vacuum applied.
Be warned because I've had experiences with parts counter people, who have no clue as they try to sell you the wrong PCV valve. Even after I specifically ask the counterperson if the PCV valve is for California Emissions. I get the response, "Well it looks the same!" They try and do the same thing with EGR valves if you let them.
Just because it looks the same, doesn't mean they are.
Getting the wrong PCV valve can cause drivability issues. Been there etc...
As for vacuum flow, I do not know which is greater. You could look at both valves, side by side and see which opening is open more, I suppose with the same vacuum applied.
Be warned because I've had experiences with parts counter people, who have no clue as they try to sell you the wrong PCV valve. Even after I specifically ask the counterperson if the PCV valve is for California Emissions. I get the response, "Well it looks the same!" They try and do the same thing with EGR valves if you let them.
Just because it looks the same, doesn't mean they are.
Getting the wrong PCV valve can cause drivability issues. Been there etc...
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Lead Driver
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From: Sheffield, AL
Of course it really gets interesting when one has a 1986 F150 4.9L which now is carbureted with a 1970 Carter YF from a F350 and this vehicle no longer has EGR.
Now I understand what my mother meant when she said, "son, leave well enough alone".
Now I understand what my mother meant when she said, "son, leave well enough alone".
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Cargo Master
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From: New Zealand
I'm only guessing here........but maybe there was an assumption that the heavier GVWR truck would be driven with a wider throttle opening (so lower manifold vacuum) most of the time - so a different valve.
Old School Hot Rodder
Joined: Feb 2006
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From: Exmore, VA
It may actually be that Ken, or it could be that the over 8500 GVW flows a little more. It shouldn't even come up unless you are looking for F250/350 parts. Up through 87 the weight break for emission class came at 8500 GVW that's why my truck never had a catalytic converter. The only gas engines offered in an 86 F350 were, 300 6, 351 HO and 460.
Old School Hot Rodder
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From: Exmore, VA
You forgot the battery for the 83 Corvette and the 65 Corsa radiator. They probably keep those right near the muffler bearings.
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From: Virginia
I did a little bit of searching, and from what I can gather, the PCV valve has two modes of operation; 1. Idle operation, and 2. Above idle operation.
I am not sure about the flow rates, I would assume that is determined by the engine size. What I did learn was different engines generate different levels of vacuum at idle. And as different things happen at idle(A/C cycles, auto tranny put in reverse or drive) the vacuum at idle can change. They want to make sure the PCV valve stays in the closed "idle" position and does not start to open, and affect the idle quality.
I would assume the same engine, equipped with different options and different smog controls, would require a different PCV valve.
I am not sure about all this myself, but it is interesting to find out what the real story is. What I picked up was on the internet, and the source was not that reliable.
I am not sure about the flow rates, I would assume that is determined by the engine size. What I did learn was different engines generate different levels of vacuum at idle. And as different things happen at idle(A/C cycles, auto tranny put in reverse or drive) the vacuum at idle can change. They want to make sure the PCV valve stays in the closed "idle" position and does not start to open, and affect the idle quality.
I would assume the same engine, equipped with different options and different smog controls, would require a different PCV valve.
I am not sure about all this myself, but it is interesting to find out what the real story is. What I picked up was on the internet, and the source was not that reliable.
Old School Hot Rodder
Joined: Feb 2006
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From: Exmore, VA
Dave, what you found is correct, at high vacuum (idle) they close down to a small orifice. The size of that is probably what varies along with the strength of the spring. I'll throw in another one, turbo or supercharged engines where the PCV valve is beyond the turbo or supercharger, need a valve that positively seals under boost, if not you have some really interesting issues.
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