PCV leak

-
To rejoin and older post, I have found an alum. straight pcv type valve that will open with any suction, for an experiment as a evac line set up , thinking it will draw all the time. I have been running an oil intersceptor/collector w/ a site tube to see if any oil is getting thru my existing pcv set up and into the throttle body , hasn`t passed any yet. Dont know about wot tho.
Very interesting
If I am reading correctly you want your PCV to "open with any suction"
On the other sided of that coin, I need to open just off idle around 11 inches of vacuum.
I want it closed at idle which on my engine is 10 inches
 
Just to be sure this is all known: The PCV has 3 'flow' rates.
  • Zero flow: With any reverse pressure (manifold pressure higher than crankcase, like heavy reversion pulses up into the intake or a backfire through the carb), the PCV will close. This is due to the check valve built into the PCV. Most guys try blowing through the PCV both ways and find it will not blow-through in one direction; this is the check valve working. This likely what FB is finding.
  • Low flow: With higher levels of vacuum in the intake, the PCV is in low flow mode. This limits the the airflow so as to not interrupt idle operation.
  • High flow: With low levels of manifold vacuum, the PCV opens to a higher flow rate.
You can't detect the change between high and low flow modes by blowing through it; you can't generate enough vacuum yourself with the low or high flow rates.

OP, what you are seeking is backwards from how PCV's work. They are in high flow mode at lower vacuum levels. I am not aware of any PCV that has lower or no flow at a lower vacuum. If your idle is such a low vacuum level, then all you can do is put in a fixed restriction and hope it pulls adequate flow.

With your current set up and adding a restriction (or if the junk box PCV simply has a lower flow rate than a stock Mopar PCV), then you will have:
  • At idle, the PCV will be in high flow mode with a restriction
  • At light cruise and just off idle, the PCV may switch to low flow mode and still have the restriction
  • At heavy cruise, the PCV will be in high flow mode with a restriction
  • At WOT, it won't matter as there is little PCV flow anyway
Hope that makes sense!
 
Just to be sure this is all known: The PCV has 3 'flow' rates.
  • Zero flow: With any reverse pressure (manifold pressure higher than crankcase, like heavy reversion pulses up into the intake or a backfire through the carb), the PCV will close. This is due to the check valve built into the PCV. Most guys try blowing through the PCV both ways and find it will not blow-through in one direction; this is the check valve working. This likely what FB is finding.
  • Low flow: With higher levels of vacuum in the intake, the PCV is in low flow mode. This limits the the airflow so as to not interrupt idle operation.
  • High flow: With low levels of manifold vacuum, the PCV opens to a higher flow rate.
You can't detect the change between high and low flow modes by blowing through it; you can't generate enough vacuum yourself with the low or high flow rates.

OP, what you are seeking is backwards from how PCV's work. They are in high flow mode at lower vacuum levels. I am not aware of any PCV that has lower or no flow at a lower vacuum. If your idle is such a low vacuum level, then all you can do is put in a fixed restriction and hope it pulls adequate flow.

With your current set up and adding a restriction (or if the junk box PCV simply has a lower flow rate than a stock Mopar PCV), then you will have:
  • At idle, the PCV will be in high flow mode with a restriction
  • At light cruise and just off idle, the PCV may switch to low flow mode and still have the restriction
  • At heavy cruise, the PCV will be in high flow mode with a restriction
  • At WOT, it won't matter as there is little PCV flow anyway
Hope that makes sense!
Thanks for the write up.
I very much understand how a PCV system works as I possess a vocational degree in internal combustion engine technology and retired from Cummins Engine Co.
What I want is a Unicorn, a PCV that has very little flow (leakage) at idle, they all flow at idle manifold vacuum.
What started this was a high idle condition due to to much PCV flow at idle, like almost 200 rpm. Now I have that down to near 100 rpm which for the most part dropped my idle speed down to a more manageable level.
The PCV is still not right, that's the price we pay for a big cam.
 
Thanks for the write up.
I very much understand how a PCV system works as I possess a vocational degree in internal combustion engine technology and retired from Cummins Engine Co.
What I want is a Unicorn, a PCV that has very little flow (leakage) at idle, they all flow at idle manifold vacuum.
What started this was a high idle condition due to to much PCV flow at idle, like almost 200 rpm. Now I have that down to near 100 rpm which for the most part dropped my idle speed down to a more manageable level.
The PCV is still not right, that's the price we pay for a big cam.

D , all of the above.
I`m trying to make/play with a simple deal that will pull vacuum at any rpm, it aint gonna pull too much in a 3 1/2'' exhaust system w/ hi flow spiral mufflers -----
 
Thanks for the write up.
I very much understand how a PCV system works as I possess a vocational degree in internal combustion engine technology and retired from Cummins Engine Co.
What I want is a Unicorn, a PCV that has very little flow (leakage) at idle, they all flow at idle manifold vacuum.
What started this was a high idle condition due to to much PCV flow at idle, like almost 200 rpm. Now I have that down to near 100 rpm which for the most part dropped my idle speed down to a more manageable level.
The PCV is still not right, that's the price we pay for a big cam.

You can do what you want with the Wagner PCV valve, but it ain’t cheap. But they are very tuneable and they work.
 
Thanks for the write up.
I very much understand how a PCV system works as I possess a vocational degree in internal combustion engine technology and retired from Cummins Engine Co.
What I want is a Unicorn, a PCV that has very little flow (leakage) at idle, they all flow at idle manifold vacuum.
What started this was a high idle condition due to to much PCV flow at idle, like almost 200 rpm. Now I have that down to near 100 rpm which for the most part dropped my idle speed down to a more manageable level.
The PCV is still not right, that's the price we pay for a big cam.
Yeah, I think you got one with a more restricted level of flow. That is all you are going to be able to do.... unless you had some sort of computer controlled PCV, with a TPS, to be be able to determine the exact operating situation LOL.

Boy, I can see it now.. a $300 computer controlled PCV kit with a bluetooth link to your smartphone. If it has an app for a smartphone, it will sell! "Sorry officer... I crashed because I was adjusting my PCV..."
 
Hang on fellas;
I fail to see a PCV problem here.
I suspect a T-slot problem, and a possible lack of bypass air, coupled with too much idle-timing.
And here's why;
my 367 has a 230/237/110 Hughes cam in it, .549/.571 [email protected];
and she will idle down to 550/500 pulling herself across the parking lot all afternoon, with
an old PCV pulled from the all-Mopar junkbox. And
with the T-slots slightly taller than wide, and
5* of idle-advance.
This is with a Commando manual trans (3.09low), and 3.55s, so the starter is 10.97 and there is NO fluid coupling.

My throttle blades have one hole drilled in each primary, to supply additional bypass air (about 3/32 each), in addition to what the PCV is supplying.
My idle-timing was determined by the T-slot setting to be 750 in Neutral@ 14*; or 700@12*.
The 5* I quoted above is done by electronic retard thru a dash-mounted, dial-back, timing-retard box. This is how you know when your T-slot exposure is set right; by the fact that it will do the above trick.

If you have an automatic you can get away with a lotta lotta errors, because the engine never sees much of a load until it gets to the stall-rpm. But with a manual trans, the tires are married to the engine, so your low-rpm tune has to be pretty dang close. And it all starts with the Transfer-slots and idle timing relationship.
I could be wrong,
it wouldn't be the first time, but I have seen it over and over and over;too much idle timing, has closed up the transfers, so the engine will not idle well even with the idle-mixture screws cranked way out. I learned this with the Mopar 292/292/108 cam, years ago.
I hope I'm wrong,
cuz I hate coming off like a know it all, way more than being wrong.

Just as a comparison;
My engine has been running the same ancient plastic
junk-box PCV since 1999. It has seen three different cams; beginning with
that 292/108 Mopar ([email protected] I believe), then
a Hughes HE 2430AL,([email protected]), and finally,
a Hughes HE3037AL, ([email protected])
The only difference was the size of the bypass holes and minor idle-timing changes, all;
same engine/same induction/same exhaust.
Yes the 223 was my favorite.
Yes the 292 was the least favorite, until it woke up at ~5000/42mph; then it screamed to 7200/60 mph, still in first gear,lol. Yeah, no,not the best idea I ever had. I ditched it before the end of the first summer.
I ran that 223* Hughes equipped iteration with several different carbs and intakes, and many different rear gears and at least one of every different Mopar 4-speeds 1x23 spline transmissions; hyup every one of them. Why? Because that 223* was a killer street cam, And I was searching for the killer gearing, to make a killer street combo..and I did,finally.
 
Hang on fellas;
I fail to see a PCV problem here.
I suspect a T-slot problem, and a possible lack of bypass air, coupled with too much idle-timing.
And here's why;
my 367 has a 230/237/110 Hughes cam in it, .549/.571 [email protected];
and she will idle down to 550/500 pulling herself across the parking lot all afternoon, with
an old PCV pulled from the all-Mopar junkbox. And
with the T-slots slightly taller than wide, and
5* of idle-advance.
This is with a Commando manual trans (3.09low), and 3.55s, so the starter is 10.97 and there is NO fluid coupling.

My throttle blades have one hole drilled in each primary, to supply additional bypass air (about 3/32 each), in addition to what the PCV is supplying.
My idle-timing was determined by the T-slot setting to be 750 in Neutral@ 14*; or 700@12*.
The 5* I quoted above is done by electronic retard thru a dash-mounted, dial-back, timing-retard box. This is how you know when your T-slot exposure is set right; by the fact that it will do the above trick.

If you have an automatic you can get away with a lotta lotta errors, because the engine never sees much of a load until it gets to the stall-rpm. But with a manual trans, the tires are married to the engine, so your low-rpm tune has to be pretty dang close. And it all starts with the Transfer-slots and idle timing relationship.
I could be wrong,
it wouldn't be the first time, but I have seen it over and over and over;too much idle timing, has closed up the transfers, so the engine will not idle well even with the idle-mixture screws cranked way out. I learned this with the Mopar 292/292/108 cam, years ago.
I hope I'm wrong,
cuz I hate coming off like a know it all, way more than being wrong.

Just as a comparison;
My engine has been running the same ancient plastic
junk-box PCV since 1999. It has seen three different cams; beginning with
that 292/108 Mopar ([email protected] I believe), then
a Hughes HE 2430AL,([email protected]), and finally,
a Hughes HE3037AL, ([email protected])
The only difference was the size of the bypass holes and minor idle-timing changes, all;
same engine/same induction/same exhaust.
Yes the 223 was my favorite.
Yes the 292 was the least favorite, until it woke up at ~5000/42mph; then it screamed to 7200/60 mph, still in first gear,lol. Yeah, no,not the best idea I ever had. I ditched it before the end of the first summer.
I ran that 223* Hughes equipped iteration with several different carbs and intakes, and many different rear gears and at least one of every different Mopar 4-speeds 1x23 spline transmissions; hyup every one of them. Why? Because that 223* was a killer street cam, And I was searching for the killer gearing, to make a killer street combo..and I did,finally.

A little differance to the subject , but I got the new single ext. pick up line done , filled the new 9 qt pan w/7 qts. , installed the interior mounted vacuum gauge line in the valve cover , ''pcv on the other siide'' , 5 '' of crankcase vacuum , I`m surprised it had that much , .0600 lift solid street roller ---------------any comments ??
 
A little differance to the subject , but I got the new single ext. pick up line done , filled the new 9 qt pan w/7 qts. , installed the interior mounted vacuum gauge line in the valve cover , ''pcv on the other siide'' , 5 '' of crankcase vacuum , I`m surprised it had that much , .0600 lift solid street roller ---------------any comments ??
Dam Bob that sounds like a lot of crankcase vacuum.
When I was a Service Engineer for Waukesha Engine we had 16 cylinder 9390 cu in industrial engines that would pull 4 1/2 inches of water column of crankcase vacuum.
You are drawing 5 inches of mercury
When you get a chance please post some pic's of you PCV setup.
 
A little differance to the subject , but I got the new single ext. pick up line done , filled the new 9 qt pan w/7 qts. , installed the interior mounted vacuum gauge line in the valve cover , ''pcv on the other siide'' , 5 '' of crankcase vacuum , I`m surprised it had that much , .0600 lift solid street roller ---------------any comments ??
DO you have any breather on there FB? Or is that hole blocked by the vacuum gauge?
 
NO
DO you have any breather on there FB? Or is that hole blocked by the vacuum gauge?

No pics, pcv hooked to both 3/8'' outlets on the back of my fast 2.0 throttle body/thru oil catch can, to see if it was oiling my intake , it isnt /no oil has shown up in it yet., no breathers , vacuum gauge hooked up to drivers side valve cover .
I got into this line of thinking fixing oil leaks. I was gong to install a pan evec system , but am wondering if its needed, Th evac system would more than likely be for higher rpm
tho.---------------------All comments appreciated----------
yellow rose
Andy
72blunblue
mopar official
RRR------------forgetting a couple !
-----------------------------------------thanks for comments so far .
 
NO


No pics, pcv hooked to both 3/8'' outlets on the back of my fast 2.0 throttle body/thru oil catch can, to see if it was oiling my intake , it isnt /no oil has shown up in it yet., no breathers , vacuum gauge hooked up to drivers side valve cover .
I got into this line of thinking fixing oil leaks. I was gong to install a pan evec system , but am wondering if its needed, Th evac system would more than likely be for higher rpm
tho.---------------------All comments appreciated----------
yellow rose
Andy
72blunblue
mopar official
RRR------------forgetting a couple !
-----------------------------------------thanks for comments so far .
Very interesting
I dont know how that system is going to circulate gases out of the crankcase without a breather in the system. That's probably why you are seeing such high cc vacuum.
Good luck, report back after some mileage.
 
Very interesting
I dont know how that system is going to circulate gases out of the crankcase without a breather in the system. That's probably why you are seeing such high cc vacuum.
Good luck, report back after some mileage.

Crankcase vacuum is supposed to create good ring seal.
You dont use breathers with pan evac system either , usually one hooked to each valve cover /no breathers..they empty the crankcase gasses , much like the pcv system is doing, the trick is will it do it at all rpms.-----???
I know of gm guys running totally sealed systems on street cars.
 
A little differance to the subject , but I got the new single ext. pick up line done , filled the new 9 qt pan w/7 qts. , installed the interior mounted vacuum gauge line in the valve cover , ''pcv on the other siide'' , 5 '' of crankcase vacuum , I`m surprised it had that much , .0600 lift solid street roller ---------------any comments ??
5inches at idle? What was your manifold vacuum at that time?
I'm surprised too.Have you measured the LeakDown? You must have a heckuva ringseal.
I got numbers half that high when I installed Plasma Moly rings on my KB107s with too tight ringgaps. It would lock up at shut-down, and the starter couldn't crank it for 15/20 minutes. I had to take the engine back out and open the gaps up some.
I gottamention tho;
I get EVACs at the track, cuz the gains are more than significant;
but if this is a streeter, anything more than 400/450 hp, IMO, is waaaay overkill, so; are you sure you want to be looking for the last few? I mean 5 inches is enough to suck something in somewhere; and the longest I ever stand on it is 5 or so seconds.
IDK; 5 inches is a lot. Yur engine is gonna implode,
:lol:
 
Last edited:
5inches at idle? What was your manifold vacuum at that time?
I'm surprised too.Have you measured the LeakDown? You must have a heckuva ringseal.
I got numbers half that high when I installed Plasma Moly rings on my KB107s with too tight ringgaps. It would lock up at shut-down, and the starter couldn't crank it for 15/20 minutes. I had to take the engine back out and open the gaps up some.
I gottamention tho;
I get EVACs at the track, cuz the gains are more than significant;
but if this is a streeter, anything more than 400/450 hp, IMO, is waaaay overkill, so; are you sure you want to be looking for the last few? I mean 5 inches is enough to suck something in somewhere; and the longest I ever stand on it is 5 or so seconds.
IDK; 5 inches is a lot. Yur engine is gonna implode,
:lol:

I have been wondering about my ring seal for some time , gapless second rings , not so concerned about them now. Must be some other reason it doesn`t run like I think it should .
W/ only 10'' tires and street gearing , I may be comparing apples to oranges tho. ---??
 
Must be some other reason it doesn't run like I think it should .W/ only 10'' tires and street gearing
Does that mean how it runs, or
how it performs?
Cuz if I remember, you said .600lift roller...... so that's pretty ugly in terms of cam-timing,lol.
And my idea of street gearing ends at 3.55s without a 5th gear,or an overdrive.
If you can marry a .600 roller with 3.55s,and with a reasonable Street Stall; hey that's a feather in your cap!
 
Does that mean how it runs, or
how it performs?
Cuz if I remember, you said .600lift roller...... so that's pretty ugly in terms of cam-timing,lol.
And my idea of street gearing ends at 3.55s without a 5th gear,or an overdrive.
If you can marry a .600 roller with 3.55s,and with a reasonable Street Stall; hey that's a feather in your cap!

3:73`s and a 3500 that goes higher than that behind the 505.
Used to race a hemi belvedere w/ 14-16'' slicks/5:38 gearing , and a hot 406 sbc vega w/14'' slicks/4:10 gearing , kinda makes the fish seem a little lack luster .
 
NO


No pics, pcv hooked to both 3/8'' outlets on the back of my fast 2.0 throttle body/thru oil catch can, to see if it was oiling my intake , it isnt /no oil has shown up in it yet., no breathers , vacuum gauge hooked up to drivers side valve cover .
I got into this line of thinking fixing oil leaks. I was gong to install a pan evec system , but am wondering if its needed, Th evac system would more than likely be for higher rpm
tho.---------------------All comments appreciated----------
yellow rose
Andy
72blunblue
mopar official
RRR------------forgetting a couple !
-----------------------------------------thanks for comments so far .
Famous funny thing is I’m running the same but 2pcv in the sniper one on each bank and has stoped my rear main leak. Have been running it this way no sign of oil in the manifold anywhere and no leaks . Have put on 6k with no issues. With 1 pcv and one breather opposite side it would leak from the rear main.
 
Famous funny thing is I’m running the same but 2pcv in the sniper one on each bank and has stoped my rear main leak. Have been running it this way no sign of oil in the manifold anywhere and no leaks . Have put on 6k with no issues. With 1 pcv and one breather opposite side it would leak from the rear main.
Have you given any thought to the dual PCVs sucking atmospheric air into the crankcase at the formerly leaking rear mainseal, because you know, that the rear main seal is designed to prevent pressure escape.... not pressure intrusion. You could consider it a one-way valve.
 
Last edited:
Have you give any thought to the dual PCVs sucking atmospheric air into the crankcase at the formerly leaking rear mainseal, because you know, that the rear main seal is designed to prevent pressure escape.... not pressure intrusion. You could consider it a one-way valve.

new rear main seal again , not tested too much yet.
A friend bought a new 502 crate motor from G M , it had 16 plus inches of vacuum , and made the rear main squeel, he put one of those wagner $75 pcv valves on it to adjust the leak. I think they adjusted it to 14 to 16 '' , stopped the squeel. My 406 sbc GMC waxed his 502 *** !! hehehhe !
The pcv valves dont do squat when the throttle is open, the vacuum is non existant then. I`m toying w/ the idea of pan evacs in the headers for wide open throttle ,been too lazy to get back under the car-------------
 
Have you given any thought to the dual PCVs sucking atmospheric air into the crankcase at the formerly leaking rear mainseal, because you know, that the rear main seal is designed to prevent pressure escape.... not pressure intrusion. You could consider it a one-way valve.
Rear main was replaced twice , plugs show no signs of oil ,checked pcv hoses going into the sniper for any traces of oil nothing , engine doesn’t burn or dump oil , Idles @ 850 rpm. I know it ain’t the right way of doing it but it works AJ.
 
-
Back
Top