I was on YB today and saw a thread that caught my attention.

The question was can you use a PCV valve AND pan-e-vacs at the same time, with a closed loop system (as opposed to an open loop system for a factory PCV set up). As was metioned in the thread, it is something similar to what Jenkins used in his book way back when.


It would seem to me a good idea because at idle and cruise you would have more vaccuum and (potentially) more oil control.


Obviously, you can use a vaccuum pump of some sort or a dry sump, but I don't want to mount an electric pump on my junk.

Thinking it through (in my head) it seems to make sense.

What do all of you think?


FWIW I would use a PCV from www.mewagner.com

Yes you can... at WOT the PCV closes due to super
low vac and the e-vac would be pulling good

At what point are engine breathers no longer sufficient? I currently don't run a PCV valve or Evac System, only two breathers. What are the pros and cons of each and in what application is each type most ideal?

The pair of breathers will work fine until you start making
positive crank case pressure(you would have to put a gauge
on the crank case).. if the engine lets enough air past the
rings it can make pressure.. a e-vac will pull a max of 5"HG
at rpm.. if you run a exhaust system that has any back pressure
then you will reduce that 5"hg by the amount of back pressure..
a PCV will work until(again)you start making crank case pressure..
also the PCV will close off when the intake vac drops near the
1" point.. as you can see they all have a limit.. a vac pump
(belt driven) tends to increase in vac as rpm goes up.. most
are set with a vac controller or some call it a regulator that
is set and only allows that amount of vac.. then it opens
EDIT
Also.. understand that a vac in the crank case helps
seal the rings.. with most of the stuff mentioned it
will only keep the crank case at zero.. its not helping
seal the rings BUT it isnt allowing it to make pressure

So have you ever run a PCV valve in a closed system? I called Gene (IIRC) at Wagner (they make an adjustable PCV valve) and he is not sure I could run a PCV valve in a closed system. I get what he is saying if I was just using a PCV valve, but with the pan e vac I'm not sure. Gene is saying to fuction properly, the PCV system needs a freah air inlet, but IMHO, in a performance application, any freah air intake would inhibit the ability to pull a crankcase vaccuum. And in reality, with out running an electric vaccuum pump (or a mechanical one) that is what I'm getting at.

What do you think Mr P?

I have run a PCV and e-vacs together.. remember that
you want a closed system.. pretty hard to make vac
with breathers... but if you run exhaust the e-vac
might not work.. check the back pressure

Very good article, and the Mewagener PCV valve sure sounds like it is the way to go. IMO, on the street a PCV system is the way to go. Only difference in closed loop verses open loop PCV systems is where you are drawing the air in from - open loop is from the opposite valve cover and closed loop is from the air cleaner. Exhaust evac systems are for racing applications only ( reads no exhaust back pressure, so no mufflers / tail pipes, etc. Don't believe what some of the muffler mfgs will tell you. They just about all create enough back pressure to shut off the evac system. If you try and run an evac system on the street, you will stand a good chance of burning out the anti-backfire valves in pretty short order. When that happens, you will pressurize the crankcase considerably more than just running open breathers. And even if they don't burn out, you still have to overcome exhaust back pressure for the crankcase to vent - much more crankcase pressure than open breathers. Yes, you could run both system, but don't know why you would want to, as one would compromise the other.

I went back to running a PCV valve and system on my 63. It pulls enough vacum to work fine and since I do 99% street driving I hooked it back up. When I race I just pop out the PCV valve and run a breather on each valve cover since the PCV will basically close off and not funtion at WOT. Ron

Not a Mopar, but I added an adjustable pcv valve to the top of my homemade separator tank and a large check valve to the end of the electric vac pump's outlet hose, basically allowing the electric pump to be turned off while the sealed pcv system becomes the sole source of crankcase vacuum during casual driving (draws 15"Hg in the crankcase even while driving down the freeway). I have ran this setup a couple years now, only problem i've had was initially sealing the engine up to handle the high vacuum. Here's a pic of the modified pcv valve added to the top of the separator tank......



The engine is now able to use narrow 1.2mm compression rings and low tension 12lb oil rings on the street. Due to the reduction of ring drag, the engine picked up about 325rpm at idle over the previous shortblock that had std rings and no pcv (no other changes).

I've got gapless top rings in the engine, 4 spd manual, 3.73 gears, and no overdrive. It's about 3000rpm down the freeway, so without a good vacuum on the crankcase it goes thru a quart of 5W-20 synthetic in about 250 miles. With the 15" of pcv / sealed crankcase vacuum, that jumps to around 800 mi per quart.

The separator tank's bottom outlet is routed to an electric vac pump due to the car using a muffler, but that electric pump only comes on when the nitrous solenoids are energized during a pass. It could have easily been routed to exhaust evacs if i had decided to go that route instead.



I cut apart a pcv valve to figure out how to make it adjustable. I cut the raised lip with my lathe to open it up, here's what was inside...



If you wanted to shim the spring, change the orifice size, etc, a simple short band of shrink tube could be used to re-assemble the valve.

In the end, the only adjustment i ended up making was to add an externally adjustable screw, allowing me to basically turn the valve into an adjustable orifice to allow pulling more vac at idle...



Here's a pic of how my vac system attaches to the valve covers, the o-ringed fittings are machined from Delrin plastic...



There are no baffles at all inside the valve covers. The large 3/4" id hose reduces velocity when air is flowing thru the system, making it less likely for that airflow to carry oil out of the engine.

Here's a quick crude example of how crankcase vacuum can help squeeze a little more power/economy from a street/strip engine...
Take two mostly identical engines, except one shortblock requires 40ft/lbs to roll over using regular oldschool piston rings, the other uses a modern low-tension ring pack and requires only 13ft/lbs to roll over. That's a constant savings of almost 8hp at 1500rpm. If your car cruises at 2500, that equals a constant savings of roughly 13hp while you are driving down the hiway. As a bonus, WOT at 7000rpm, the low-tension shortblock would have about 36 more hp on tap. The engine will run cooler with less ring friction, and the bores will show a lot less wear. If adding a crankcase vacuum system allows you to use a lighter ring pack, it won't take long for it to pay for itself.

Moroso and some other maker use to sell a combination kit that used a PCV and the header evac system together for drag racing I'm not sure if they still do or not I never like the header draft tube evac system only due to the large amount of condensation they would pull into the valve covers I went to breathers only or dual PCV with dual breather caps, one per valve cover on each side on my last street strip car The standard PCV system will help suck the moisture out of the crankcase

Yes, what PCV systems do best ( remove moisture) and why every street car should have one. For race cars, moisture is mostly a non-issue. For exhaust evac systems to work properly, you gotta have a sealed crankcase - no vents, no PCV.

Cab.. why have breathers on anything that will try
to make a vac... you want it sealed up... if you have
it sealed it draws out any moisture

So it sounds like I will give the wagner PCV valve a try, and use the pan e vac system. I use a muffler that I think makes very little back pressure.

Other than hooking a manometer up to the crank case, how do I tell how much back pressure I have?

Put a pressure gauge on the exhaust... dont put it
on the crank case if you want to check the exhaust
EDIT
if you have the e-vac nipples on the pipes already
then hook up to them

When I used the Mr Gasket evac system with the the hoses from the pushin beather cap with the hose slid onto it and then down to the header collector with the GM anti backfire valve on the header nipple years ago I would always have moisture and oil condensation mixed together under that cap in the valve covers after several races Once I went to breathers only, no evac sytem, no more moisture under that pushin breather cap On my current car I have a GZ vacume pump with real thin low tension rings for that build It sucks some moisture out of the motor, I run it on E85 with a little tiny cooling system on that car, the only thing I see come out of the catch can for the vacume system is condensation moisture