excessive 340 crankcase pressure

-
It looks like the OP has 2 PCV's tee-ing together, then to the catch can, and then back to the carb's PCV port. If that is the case, it will indeed absolutely draw a vacuum in the crankcase with 2 PCV's; you don't need airflow in create a lower pressure in any closed chamber. (The inflow of air is actually going to be from the blowby... not a good source for keeping the crankcase clean, but a source nontheless.)

Regardless of whether the OP has a breather or not, at high RPM's, there will be the most blowby and the least flow into the PCV port on the carb as there is almost no vacuum there at WOT, regardless of the number of PCV's or the type. In that case, adding a breather may help as it will reverse flow at WOT and become a fairly open vent for the crankcase pressure. At least the dipstick may not blow out oil.

OP, when you say there is oil mist out of the dipstick tube, is that at idle? Or are you just seeing the results after WOT operation?

And, I can't read the label on the hose connected to the PCV's valves but if it is fuel line, using that is a no-no. Proper PCV hose will not collapse inward under the vacuum pressures in the hose; fuel line can collapse.
 
I already knew how it was done from the factory cause I have a 70 340 Duster and a 72 Swinger. Both with all o.e.m. parts. I was just testing the old dude to have fun and RRR knew what I was talking about.
 
nm9stheham said:
It looks like the OP has 2 PCV's tee-ing together, then to the catch can, and then back to the carb's PCV port. If that is the case, it will indeed absolutely draw a vacuum in the crankcase with 2 PCV's; you don't need airflow in create a lower pressure in any closed chamber. (The inflow of air is actually going to be from the blowby... not a good source for keeping the crankcase clean, but a source nontheless.)

Regardless of whether the OP has a breather or not, at high RPM's, there will be the most blowby and the least flow into the PCV port on the carb as there is almost no vacuum there at WOT, regardless of the number of PCV's or the type. In that case, adding a breather may help as it will reverse flow at WOT and become a fairly open vent for the crankcase pressure. At least the dipstick may not blow out oil.

OP, when you say there is oil mist out of the dipstick tube, is that at idle? Or are you just seeing the results after WOT operation?

And, I can't read the label on the hose connected to the PCV's valves but if it is fuel line, using that is a no-no. Proper PCV hose will not collapse inward under the vacuum pressures in the hose; fuel line can collapse.
Click to expand...


1, 2 or 12 valves doesn't matter. A single valve will outflow what the carb can take in.

If the OP wants to draw a vacuum in the crankcase, then he needs to seal the engine, run no breathers and let the PVC system pull a vacuum. The issue is that won't do anything at WOT or any other low vacuum situation.

In that case, the OP needs to run some other system, like a pan evac over the top of the PCV system. At idle the pan evac will do very little, but the PCV is working. At cruise, both systems are working and that's when they both pull the most vacuum. At WOT you are relying on the pan evac totally as the PCV system is doing nothing..


I guess I'm just dumb. If the normal, OE system RRR posted above won't control blow by for the OP, he is just mentally masturbating and beating his head against the wall. The OE system is more than capable of handling blow by.

If it won't work, it needs ring seal work. No PCV or evacuation system will fix that.

Again, I ask has a leak down been done on the engine? If it has, what are the results? If not, why not?
 
I do NOT think this is a "ring seal" problem. I do NOT think he needs to do a leak down check as of yet. He has already done a compression check.
Fix the mistakes then chase a big problem "IF" it exist. There is no big problem!!
This post has gotten out of hand. He has some great advise and if he follows it his problems will be gone.
 
pcv-system-gif.gif


You see that rubber hose going to the aircleaner? It's there for a reason. At WOT the system reverses and sends the blow-by into the air cleaner instead of blowing the dipstick out and messing up your Vcovers.
Thanks RRR for the swell diagram
 
Last edited:
well then live with what you get and quit whining about the dipstick acting like a blow-off valve.
and good thing it does, cuz if it didn't, maybe the rear main seal would blow out, or worse,the rear cam plug. 5psi crankcase pressure on a 2" plug comes to almost 16 pounds of force; hope you glued that plug in...... That hose will be really really cheap compared to replacing that camplug...... a quality piece of heater hose has lasted me for nearly two decades It mightabin $1.25 a foot back in '99
'Course; file-fit Plasma Moly second rings do a pretty good job of reducing the blow-by to a minimal amount.
 
Last edited:
What is so hard about understanding this? Simple principle, fresh air in one side and regulated suck on the other. If anyone has an issue then put in a draft tube like the really old engines. Cummins used this into the 2k range on the 5.9 killer diesels! This issue has been beat to death and few learn.
 
1969383S said:
What is so hard about understanding this? Simple principle, fresh air in one side and regulated suck on the other. If anyone has an issue then put in a draft tube like the really old engines. Cummins used this into the 2k range on the 5.9 killer diesels! This issue has been beat to death and few learn.
Click to expand...

Regulated suck. Sounds like a girl I knew in school.
 
IMHO if you're running a PCV valve/ vent set up and blowing the dip stick out or oil out of the vent you have ring issues.

I've been messing with Mopars since I was in high school in the mid-late 70's. Both big blocks and small blocks and all I've ever ran was a PCV valve in one valve cover and a breather in the other and never had any issues with blowing the dip stick out or blowing oil out of the breather in the valve cover unless the ring seal was bad. My current 434" small block turns 7200 and doesn't have any issues. The PCV valve in it is probably 15-17 years old and came from Advance Auto Parts, nothing fancy.
 
justinp61 said:
IMHO if you're running a PCV valve/ vent set up and blowing the dip stick out or oil out of the vent you have ring issues.

I've been messing with Mopars since I was in high school in the mid-late 70's. Both big blocks and small blocks and all I've ever ran was a PCV valve in one valve cover and a breather in the other and never had any issues with blowing the dip stick out or blowing oil out of the breather in the valve cover unless the ring seal was bad. My current 434" small block turns 7200 and doesn't have any issues. The PCV valve in it is probably 15-17 years old and came from Advance Auto Parts, nothing fancy.
Click to expand...

Possibly. But which is easier to do right off the bat? I vote that he get the PCV system straightened out first. It's free or almost free. The leakdown test will tell him what's up if "that" doesn't fix it.
 
RustyRatRod said:
Possibly. But which is easier to do right off the bat? I vote that he get the PCV system straightened out first. It's free or almost free. The leakdown test will tell him what's up if "that" doesn't fix it.
Click to expand...

Yes, I should've posted a "correctly functioning PCV set up", if it isn't working all bets are off.

BTW the 434 made 3 more HP with the PCV valve hooked up over just the one valve cover vent and no PCV valve.
 
justinp61 said:
Yes, I should've posted a "correctly functioning PCV set up", if it isn't working all bets are off.

BTW the 434 made 3 more HP with the PCV valve hooked up over just the one valve cover vent and no PCV valve.
Click to expand...

It might just be me. I'm lazy as HELL. So I always choose the easiest thing first. LMAO But a lot of times, I've been right.
 
What the OP has (the three pictures including the separator) is not a functioning PCV system from what I can see. Rings are probably ok - but the sytem isn't working the way it should. One PCV in a valve cover, one breather on the other side and no separator. It will function just fine. If the OP wants a separator for that 2 horsepower it gives the Hellcats and so import and new musclecar guys can love him instead of being confused by the lack of technology - plumb it between the PCV and the carb nipple, and I would not pace it well below the level of the valve cover.
 
I the only thing I have to add is move your fuel line. No need to preheat your fuel with the heater hose. I would bend up a steel line or get the fuel line kit and if you ever go to a track they are going to bounce you for more than 12” of rubber line
 
You must log in or register to reply here.
-

Back
Top