Valve Cover Breathers and PCV Valves

[nolastyankee]

All,
I recall some discussion on this topic a while back, but I could not find the answer through several searches of this site.

I understand the need for crankcase ventilation, and I know there are several schools of thought on how to accomplish this. The bottom line for our car is that our new EFI stack manifold does not have a pretty way to plumb a PCV valve, so I would like to get some opinions on whether or not I can achieve proper crankcase ventilation through valve cover breathers. I know that you FE guys run double valve cover breathers and one on the intake. Looking at the old 289 Cobra comp cars, double breathers were standard. Is there any reason to think that I couldn't set up our valve covers with 2 breathers on each side and accomplish the same thing?

Unique 9122 - 289 FIA Cobra - The Legendary "Spence" Car

[rdorman]

You can run just breathers. It is better than nothing. Although it will usually create a bit of a mess. There is no place to tap the manifold for vacuum? How about spacers for a vacuum source? After all, it is called POSITIVE crankcase ventilation for a reason. Breathers = crankcase ventilation. Idealy one valve cover will have the PCV going to manifold vacuum and the other attached to the air cleaner. Of course with the gorgeous setup you have, that do appear to be a challenge!
Rick

[eliminator]

Brian,

See the old thread on "how about engine pictures everyone", then look at Butch's 289 engine. No mess, you don't need positive crancase ventilation (PCV). I am running one breather per valve cover on the 427 with no problems or mess.

Rick
#4279405

[K.Wilson]

Brian,
The PCV System has more to do with engine life and less to do with polution than most people think. Yes, it is a good thing that the products of the combustion process that blow past the rings and valve stems are captured and re-burned in the combustion process; however the secondary benefit of an engine with clean filtered air constantly carrying away the products of combustion so that they can't condense into harmfull acids and corrode the internal engine components is the greatest benefit to the car owner.
Prior to the early '60s engines had a "road draft tube" that extended down the back of the engine into the air stream under the car. This tube had a 45 degree angle on the end to create a vacuum on the tube when the car was moving. Engine vapor evacuation was poor even under the best of conditions, even worse during cold conditions when moisture in the tube would condense and freeze.
I am going to use a Weber system on the GT 40 I am building so I will have the same problem. My solution is to drill and tap all 8 intake runners on the bottom side of the manifold and run tubes to a central vacuum block, then mount the PCV Valve to the vacuum block under the manifold. The PCV valve will be inside the engine with all the tubes so you can't see it. All you will see outside the engine is a breather on one valve cover or a tube on one valve cover running to a breather filter on the firewall.
Some of the race car guys use an electric vacuum pump for this purpose, but it seems like this could be a maintenance problem for a street car.
Hope this helps, Keith

[nolastyankee]

Keith,
I like your solution! If I understand correctly, you will be taking intake runner vacuum to a central block under the intake with a PCV stuck on the end of it. The PCV will be open to the air in the lifter valley? This will circulate the air from the valve cover to the lifter valley, but do you think you will sufficiently evacuate the crankcase without drawing the air all the way through?

Given that Cobra's tend to be low mile, highly maintained cars, is the engine life argument still important or are we talking a significant change? If race cars bother with electric evacuation pumps, it seems like it would be worth the effort to figure out a way to plumb the PCV.

Unique 9122 - 289 FIA Cobra - The Legendary "Spence" Car

[rdorman]

Race cars do it for horse power. I recently saw a back to back dyno test of a motor with just breathers and a motor with a vacuum pump for crankcase ventilation. The difference in the two runs was over 20HP in favor of the vacuum pump and that is even with the additional parasitic drag of the pump! Positive Crankcase ventilation is a win-win in all catagories.
Rick

[K.Wilson]

Brian,
I can't take credit for the idea. I saw it in a photo of a weber manifold that someone was selling on E-bay.
Yes, each intake runner is drilled and threaded and what looked like 3/16 brake line was routed to an aluminum block (it looked like 1"x1"x4", with four lines running to each side)then the PCV Valve was pressed into the end of the block (I guess it could be bonded in place with RTV). The line length was not equal so the flow to each intake runner was not equal but I guess that would probably not mean much as the air flow per cylinder is relatively small.
On the topic of where the PCV Valve should go; traditionally air was taken in from one valve cover then taken out by the PCV from the other valve cover. I have looked at several manufacturers in recent years and I have seen all types of variations of configurations that include the front or the back of the intake manifold or one valve cover only etc.
I would think that any PCV system in any configuration that gets the combustion products out of the engine and clean air in the engine would be better than a road draft tube.
I am looking forward to seeing you and your Dad again at HC. With the car I hope!
Keith

[eliminator]

It's only a win if your pulling in crankcase air.[^]
Once you start pulling in oil mist and oil it is not a win.[V]
With the vlave covers on these cars being un-baffled or poorly baffled its not a win.
The lifter valley is the best place to evacuate the crancase if it is possible. That's why peple like George Gessford at Gessford Machine make a device that holds the PCV valve in a device with metal mesh basket and place it on the rear of the FE intake where the breather snorkel usually goes.

Rick
#4279405