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Proper crank-case venting with mods - 78 Midget

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As for your first post (2 above)-
if you use a catch can then don't use the PCV valve, it won't do anything if hooked-up this way. It will only work on a "sealed" system.
If you just run a 1/2" line from the front breather to the PCV valve (4-cylinder kind) and then straight to the manifold then it will work.
Otherwise just run a 1/2" line from the breather to the catch-can and leave the fitting on the manifold plugged. The car will still leak oil but you will have a catch-can as a "conversation starter".
Bill
 
Ok, that's starting to sound right to me. Common sense tells me that Bill is right on. I think I would rather avoid that catch-can system and go with the PCV, especially since that's how the car was originally set up. To my mind and in theory, the canister on the timing chain cover, which has a built in foamy filter of some sort on its interior, already acts as a baffle/catch-can to keep heavy oil in the tank and only let the fumes pass easily. I think I'll see if I can find a standard PCV, maybe off a Honda or something, (not a Hemi!) to try and regulate the ratio of manifold vacuum to crankcase pressure. Thanks for all the input!

JACK
 
Couldn't you otherwise use a "metered orifice" instead of a PCV? That's how mine is (at the moment), not that I have any idea what is best. I don't have the timing chain cover breather thing (early 1098), just a hose from the valve cover to a fitting I installed into the Pierce intake manifold (for a Weber), at that fitting I restricted the opening down to about 1/16" and my engine leaks disappeared (all but one at the spin on filter adapter). A valve may well be better and easier but many cars use this "metered orifice" aka; small opening approach. I have not approached this scientifically, like change the size of that opening, or play any other games, I hooked it up, the leaks stopped, I moved on.
(truth be told, during the install I found the fitting coming out of the valve cover a bit on the loose side so I could well have been loosing vacuum there and it could be all I ever had to do was tighten it and leave the hose going to the weber's "long flow" style air filter, but I wasn't about to reverse it just to see)
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I am going to disagree with Morris-
The PCV valve should(and will) stop a backfire from going into the crankcase but it also restricts the volume of air going from the crankcase into the intake. As someone back a few notes said it allows "wide-open" air flow when there is low-vacuum in the intake (at higher car speeds) but only allows partial open air flow during high manifold vacuum (ie. at idle). This gives you a more constant air draw and allows less oil to be drawn up into the intake.[/QUOTE]

I think you've got it reversed... think about it: all a PCV valve is sprung valve. Pressure from the manifold side overcomes the spring and shuts the valve. That's all there is too it. Pick up a fresh clean PCV valve and inhale through it and you will see that the restriction is minimal.

The valve you describe would be great, but in my experience, that isn't a PCV valve. My set up is similar to Jay's in that I use a metered orifice. The catch can helps reduce the amount of oil I burn a little.

On most modern cars, the PCV system connects to the tube between the air cleaner and throttle body. In this way, when engine load is high, there is greater air flow and a kind of venturi effect pulls the air out of the crank case. I believe Nigel built a similar set up for one of his cars.

I can't speak for the A-series engine, but the 1500 needs lots and lots of vacuum on the crank case (and an oil catch can) to keep the drive way clean. Or maybe a better engine builder than me. :wink:
 
Hey Ed, is your car blowing a lot of oil or is it just a little? I have seen it where the dipstick gets blown up almost out of the crankcase. When mine did it I could pretty much change the oil by draining it all through the dipstick. I ask that cause the catch can is a good fix as I seen a lot of guys do it that way, but if your oil issue is a bit more severe depending on the internal engine condition, that catch can may not resolve the issue and become a headache you need to check every time you drive the car. I need to get some pics already of my setup. What I did was easy once I got the pieces parts I needed and the mechanic tested and checked the engine operation and approved of the way I had it. Im going to try and get the car out tomorrow if the weather cooperates and I will send some pics.
 
It was leaving a pretty good trail of oil as I drove it. I found the darn catch-can (front of timing cover) capped off by the PO. I have had my carb on the bench for 3 weeks waiting for the rebuild kit (man, I hate waiting for parts), so I have not been able to drive it since I put the modifications on. I want to kind of play with this to see what works best since I've had so many opinions. I'm starting with a breather (small K&N type filter/breather on the vacuum line) off of the timing cover and capping my air filter intake. Once I get the carb back on and get it running I'll see how it does. Then, I'll hook it to the air filter and test again. Then, I'll put the PCV valve in and test. And last, I'll put the catch can set-up on (which might be redundant of the timing cover catch can, so I'm not sure this makes sense to do at this point).
 
Morris
I agree with you, the PCV valve IS just a restricted orifice! It is just that it is a VARIABLE restricted orifice. When the manifold is sucking really hard (at idle) the PCV restricts more and when the manifold is not sucking really hard (running speeds)the PCV opens up more to allow more flow. That way you don't have so much draw at idle that the manifold brings liquid oil up the tube and into the engine (lots of exhaust smoke) and also pulls enough volume to keep some draw while on the road to prevent drips out of the rear main "seal".
Bill
 
If you guys making your own crankcase vent systems are curious as to another approach.

Grumpy Jenkins, the chevy drag man a couple decades ago, did a treatise on using exhaust pulses from the extractor(header) to scavenge crankcase vent... He was mainly trying to suction the pressure from the crankcase to "free up" power..

I don't know exactly where in three possible storage sites, my copy of his book was. It's the 8 1/2 by 11 cardboard HP type book you get at the speed shops.
Might be able to search it off the web, google or amazon or ebay....
 
David Vizard also covers that same system in his "A-block" book (my 1985 version at least). He says that it works well too.
Bill
 
Ed
That "exhaust savaging" system is kind-of exotic and not commonly done, ignore it.
Just put a cheapo PCV valve from Schucks in line between the front can and the manifold and call it good, just be sure that you put it in the correct direction such that if you blow softly thru it in one direction it changes when you blow harder thru it (that 2-stage action) but if you blow thru it backwards it either doesn't change or it blocks the flow completely. The direction that has the 2-stage flow is the direction that the gasses must go when going from the can to the manifold.
Does that make sense?
Bill
 
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