What am I missing about vacuum?

3

36tbird

Well-known member
Here's where I am. I have an Eddie Meyer 2x2 manifold for my 59A. I want to hide the PCV under the manifold as others have suggested here by drilling into each plenum, 1 per side, and installing a screw in type PCV into this plumbing. Talking to the NAPA guy today, he told me that this PCV with 1/4" NPT applies to a bunch of '60's cars that range from small blocks to big blocks.

Now, here's my thinking about PCV's. I know from Bruce how they help remove the moisture and therefore the sludge. Then, I think about the old top oilers. Seems to me that a PCV system can act like one of those top oilers to burn a bit of the oily mist from the crankcase. So, this is all good stuff except I cannot figure out in my feeble mind the disparity in the vacuum being siphoned off in these two systems. Again, the PCV that guys have been using has a 1/4" NPT hole while the old top oiler adapters have little tiny holes for vacuum. Should the plumbing for the PCV's that guys are installing under their manifolds be reduced down to those pinholes to keep up the vacuum for the engines?

Now, another difficulty. I want to run a late style distributor on my 59A and have purchased one of the front drive adapter sets. I want to use one of Bubba's Chevy dizzies with the Accel adjustable vacuum pot. I'm thinking of tapping off of the PCV plumbing from underneath the manifold and running a sealed line in the old manifold with a nipple screwed through a hole in one of the flat spots.

So, the basic question is, I want to run a PCV and a distributor vacuum, how do I control too much vacuum loss? Thanks in advance. (Get it? Advance for the distributor?)
 
The PCV valve is designed so as to restrict flow at high vacuum. There is a spring and a tapered plug which controls the flow. There should be no loss of vacuum through the distributor as this is a closed system.
 
I only use a low vacuum PCV setup with a Chrysler-style baffled oil breather cap vented to a Chrysler-style air cleaner cannister. Don't use a high vacuum PCV valve.

Jack E/NJ.
 
Use a pcv valve from an application that is close to the displacement size of your engine... Maybe a 240ci Ford truck engine, or a 250 ci. Ford car... Can't remember what I did, but I found a 1/4" pipe threaded pcv... Could find it my notes, send a message if you wish... Karl
 
Pretty sure the PCV closes at high vacuum to keep from pulling the oil out of the system. I would think that you will have two aspects to consider. Relative vacuum pressure and volume of air flow to sustain that pressure at volume of flow. If a system is designed to pull a vac of 20 through a 1/4" line it may not be able to pull that same vac at a 3/4" or 1/2" line due to volume of vac air flow. Most likely the best thing to do and easiest will be to reproduce the stock port sizes to match the most likely volume of air flow that the vacuum of the system will support. Short of matching this sizing you may have to use a valve system that is used to restrict air flow volume to balance the system. Generally the PCV should be designed to draft the internals of the block pulling the gases and residuals through the combustion process. It is important to introduce air as well as draw air. When placed into the proper point in the carb there is usually an increase in RPM and efficientcy, this also increases vacuum volume.
 
Somewhere, either the HAMB or here, is where I found list of possible PCV's to use, Fram FV100, Borg Warner PCV255 and NAPA CRB29255. The NAPA one is what I brought home. I can suck on the threaded end and air flows easily. This is the end that I thought folks were threading into a fitting that accessed the two sides of the manifolds. If you blow into the threaded end, it seals up and prevents flow. This leads me to believe that this would prevent any backfire from belching into and possibly lighting off an oily mixture of crankcase fumes. So, you would tune for the air coming in through the PCV all of the time and it only closes in the case it senses back pressure. In my mind, that would explain why this PCV is listed for such a broad range of cu. in. engines.

I have a PCV on my 8BA from the gent who sells them on Ebay. The PCV he uses only has about half the inside diameter of these screw in ones. From that, I'm thinking about putting a plug in the screw in PCV hose connection side and drilling it with a hole the size of my 8BA PCV. Maybe that would help to keep the vacuum up. Thoughts?
 
I think that if you could run a test pass or have a bench mark group of vacuum numbers from a similar equipped engine. This way you would have data in the event you had some troubles. Is there a way you could get the engine running proper and then modify it's vacuum system? I think you are right about the PCV, she would sure go off if a vapor load got into the block.
 
Dawned on me last nite that I can run an easy test on my 8BA '36 pickup. I have the aftermarket plug in the down draft with the PCV in that. My vacuum source is a heater plate under the carb. I have the tube running from that to the PCV with a T in the hose for my distributor. It is currently plugged because currently I have one of Bubba's mechanical advance only Chevy dizzies. Last time I checked the vacuum off the T with the PCV I think it was about 14 #'s. It dawned on me that I could run the same test, pull the PCV out and plug it to see what my total vacuum available is. May try to do this today and come back with a report.

Is there an easy way to set up a vacuum pot if I were trying to engineer this bigger PCV with the screw in end down for the 59A?
 
Gentlefolks, unless the vacuum ports on the carb or manifold are specifically engineered for a particular PCV valve, I question the effectiveness or even the advisability of tinkering with a flathead's vacuum ports to try to accomodate one. However, I do feel some kind of active ventilation is better than the passive techniques used during the flathead era --- the simpler the better --- not only for helping to reduce sludge but also crankcase fumes/stench in the engine compartment and elsewhere inside the car. This is why I chose a simple PCV setup mentioned previously using the carb's low vacuum side, ie its air-cleaner cannister, fed by a baffled breather cap/tube near the rear of the intake manifold (fuelpump hole) and the existing crankcase pan vent in front (wrapped in air filter screen) now as a fresh air inlet. This setup makes a huge difference in how my garage and clothes smell during and after a hard run. 8^)

Jack E/NJ
 
So Jack, is this a 59a you are talking about? If it is and I got this right, you are drawing air into the crankcase from the front stand pipe that runs down to the oil pan vent hole and you are sucking it out at the rear of the manifold into a PCV located on the air cleaner. This has me thinking that the rear oil filler tube on a 59A could be capped off and just be made removable for the purposes of adding oil so that it is not a redundant air source. Hmmm.... I think your idea could greatly simplify what I am trying to do while maintaining aesthetics. Any pics of the connection between the air cleaner and rear manifold fixture? Thank, Lou
 
I'm sure a PCV is a good thing. It's something I've been meaning to do ever since I built my engine 17 or 18 years ago. I had my engine out this summer to correct a blunder on my part(lock washer dropped down the intake), and that engine is as clean inside as the day I built it. Probably has 50,000 miles on it. This is with the early style fill and breather.
 
Hi Lou:

The first picture below is my current PCV setup with electric fuel pump(early '38 21-stud). It's a home-made 'cigar-box' for a modern rectangular pleated air filter fed by a 1"+ id aluminum crankcase vent tube affixed to the mechanical pump/filler hole on the intake manifold. The main air intake faces the firewall when it's in the car. The vent tube is baffled with a mesh made from a grocery-store stainless steel scouring pad. 8^)

The second picture shows a Mr. Gasket repro of an old baffled Chrysler-style breather cap that I used earlier with the original mechanical pump tower. It had a PCV hookup for a 5/8" id hose that was connected to the hookup of a small round air filter cannister from a 60-70s era single barrel. It was less obstrusive and more original-looking than my current cigar box setup but the air filtration probably wasn't as good.

I've had a similar setup on a '55 265 for many years using its road draft tube covered with a screen filter, a Chrysler-style filler cap and an air filter cannister with a PCV hookup for a Rochester 2-bbl. Changing valve cover gaskets from time to time over the years revealed fairly spotless springs, rockers and other innards hiding under the covers similar to Flatjack's findings. Keep it simple.

Regards,

Jack E/NJ

pcv.jpg


PCVcap.jpg
 
Jack, you've given me some great ideas on how to do the PCV and not disturb the vacuum sources off of the sides of the manifolds. I am going to drill into the manifolds to draw air out of the lifter valley and go into a PCV mounted on the air cleaners. Thanks, Lou
 
Please Lou, don't drill holes in your manifold. Can't you somehow use the hole that's already in manifold's fuelpump tower area? It accesses the valley and the crankcase already.

Jack E/NJ
 
And remember, this is a low-vac, hi-flo PCV setup. So you need a fairly big diameter hole and hose. So an oil filler hole is a prime candidate.

Jack E/NJ
 
Jack, the way I see it, I am going to have a stock type tube going down from the oil filler mount into the block around where the fuel pump actuating rod goes. So, that tube brings in the outside air into the crankcase. Now, normally, the front stand pipe would vent down the front of the block out the oil pan vent, but I am going to block off the top of that tube. Therefore, the crankcase gases will not come up into lifter valley through the holes in the center that are baffled by the covers that snap onto the horizontal oil tube that routes the oil to the cam and main bearings. So, if I cut drill a hole in the fuel pump tower area as you suggest, wouldn't I be sucking off the inlet air?

Or, are you suggesting a reversal of the crank case ventilation flow? That is, the outside air comes in from the oil pan vent and you are sucking the air out of rear oil filler tube. Do you have the Mr. Gasket oil breather caps on the top of your rear filler tube inside your air cleaner box? Maybe that's the part I'm missing here.
 
Lou wrote:>>>Or, are you suggesting a reversal of the crank case ventilation flow? That is, the outside air comes in from the oil pan vent and you are sucking the air out of rear oil filler tube.>>>
Yes Lou. It's indeed reverse flow. That's why I wrap an air filter screen around the pan vent. And I don't block the front standpipe. So it sucks the valley out as well as the crankcase. Before I switched to an electric fuel pump, I originally connected a 5/8" hose between a Mr. Gasket-type PCV breather cap atop the mechanical pump tower and a small 60s style PCV carb air cleaner. No mods to the pump tower whatsoever. The reason I can't show you a picture of that setup is because I took it off the motor when I switched to an electric pump. .


Lou also wrote:>>> Do you have the Mr. Gasket oil breather caps on the top of your rear filler tube inside your air cleaner box?>>>
There's no Mr. Gasket breather cap when I switched to the electric pump. I simply replaced the mechanical pump tower with a baffled aluminum tube fed directly into the bottom of my pleated paper air filter cigar box . That's the current setup you see in the first picture.

If you want to maintain original-looking appearances and keep the mechanical pump tower, I'd go with the Mr. Gasket PCV setup with some kind of a small 60s style PCV carb air cleaner like I did before going to the electric pump. No modifications of the tower are needed. Just replace the cap with a Mr. Gasket PCV style cap.

Jack E/NJ
 
Hmmm, Looking at this air box I am wondering if it could be made more efficient with some form of an airflow venturi set up. With this box upon the carb set up you almost beg to take things further with airflow modifications on the engine. Follow me a bit on this, I am running an electric fan on my engine, now my engine is a later model but I still feel my findings are relevant. My engine can run for as long as 15 minutes prior to the fan turning on, this allows a cool air supply to be drawn in. As soon as the fan kicks on the air is pushed back into the engine compartment. The RPM drop is from 1000 rpm to 800 rpm just due to the airflow characteristic. I mocked up a prototype air induction system for under my trucks hood and have been putsing with it. I notice a 25% fuel economy improvement and must have at least 40 more horse power.
Given that you have an engine driven fan and an engine set up that operates almost fully within the heat of the operating engine you most likely will never experience this difference in performance. With this box upon your carb you can bring in air from away from your hot zone on your engine and supply it with cool air. If you can ventilate your crank case into this cool air source you would expect to see gains in line with mine.
If Jack took his air intake for his air box and pulled it from in front of his radiator and did this while his engine was running, he would have a big grin on his face, I did.
 
Thanks again, Jack. I think the light bulb finally came on for me. Difficult to express what I will have to do to put in effect your modified crankcase ventilation system. So when I get it done, I will try to remember to post a picture here. I think it will turn out pretty neat and should greatly simplify PCV installation on especially the pre-'49 flatties and keep the available vacuum for the distributor high. Happy New Year, Lou
 
Frank, I think the ram effect outside air is certainly something to explore. Something else to consider: A buddy and I both run risers under our Strombergs. I initially did it so that I could get the front bowl mounted on a Super Offy 2x2 to clear the back of my alternator keeping the alternator mounted as low as possible. What we discovered was how cold to the touch those risers get due to the venturi effect. My thinking is that it really cools the fuel/air mixture to make it denser, probably a variation of the same thing you are doing by introducing the outside air that is cooler than that in in the engine compartment. If we keep up with all this R&D, we should soon have our flathead powered NASCAR ready to go. Happy New Year, Lou
 
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