Small Block Chevy Venting Question.

Thanks for clarifying. I meant that by over venting the vacuum wouldn't be strong enough to pull the vapors through the engine and into the intake at idle and cruise. I don't think any harm would be done.

 

Yeah I like the look of the fill tube (kinda the reason I bought the intake) plus all that $$ for the OTB Gear cap. So it's pretty much staying like it is. I'll probably just put an oil cap on the driver side and the PCV in the passenger side & just leave the breather in the fill tube. Thanks for all the replies.

 

Is it true that the "best" location for the pcv is the back of the passenger side valve cover and does it make a big difference if your breather is to the front of that valve cover with the pcv on the driver's side toward the back? Just curious.

 

The flow will follow the least path of resistance, shortest distance between to points. But I guess venting is venting in the grand plan. What looks good to you and the type of intake/carb combo used. Some carbs have side mounted pick ups some in the rear, all these come into play when routing hoses.

 

I think the idea is to get cross flow in the engine, either front to back in the valley like the early road draft and PCV systems, back to front of the valley like some late '60's systems, or side to side across the valve covers like the late systems. Just seems in and out on the same valve cover would not be ideal. But these are hot rods and everything doesn't end up just right and still works OK.

 

Sorry Jim. Didn't mean to disparage your breather, just trying to point out a way to simplify without extra stuff.

 

................................................Thanks, Rich. I probably didn't explain that too well. I have it set up side to side, I just have it with the pcv on the driver's side towards the rear and the breather on the passenger side towards the front. Kinda unconventional for a SBC and I wondered if it's less efficient this way than with the pcv on passenger side toward the rear (where I most often see it) and the breather on the driver's side. I've read somewhere that the pcv is most efficient when positioned over the oil pump. Is this the case or is it over-thinking?

 

Over thinking my 2c.

Position over the oil pump? Never heard of that before, could someone explain? Not that it matters to me, just interested in the reason.

 

OK, so if I have the vet oilfill tube with the PCV port and the sealed cap, where is the best place for a breather if the valve covers have no holes? I'm thinking either drill a hole in the back of the intake or drivers side valve cover, install a fitting and hose, and attach a breather out of the way. Any better ideas?

 

I have used a vented cap on the oil fill and a PCV mounted in the fuel pump block off plate. I did plug the fuel pump rod hole to keep oil from coming down.

 

This set up is much like what I have on a 305. I reversed the DS valve cover to move the breather towards the rear, mainly because it's less noticeable with my set up. I suppose you could say it works because it moves the breathers farther apart but I don't think it makes any difference. I just know it works fine.

Gary

 

I'm still not sold on the idea I saw but,,,,

I spent some time with a car, the frame was boxed and at the rear near the bumper were some speed holes. From each of the valve covers were two fabricated blocks and hoses into the frame rails. Each frame rail acted like a road draft tube and had a nice rust resistant oil vapor passing thru it as a plus. There was just a oil filler tube vent. It was a super sanitary set up, couldn't even see the damn things at a casual glance. Want to know how I noticed them?? I spotted something odd and starting Wondering why the ass end of the frame was kinda oily - WTF is that from?!?

 

Hey everyone. Question...as it doesn't look like its been brought up at all.

My SBC is a goodwrench 290hp motor that needs the PCV. I have original 7 fin Corvette valve covers that I do not want to run breathers on. I'm using an old Weiand WCVSQ 4bbl intake that has a breather cap oil fill tube and has a flat area behind the carb that I ended up drilling/tapping for a PCV. Under the intake I had a baffle tig welded to keep the oil from being sucked up. I ran an inline PCV valve from the fitting coming out of the back of the intake to the front vacuum port of the carb. After running the engine a few times and not getting a smooth idle while the trans is in drive I decided to change the carb gasket as the one I originally put on it was a cheap one. When i pulled the carb off I noticed gasket was really oily which makes me believe that the baffle I had welded under the intake isn't doing anything. The oily air is still getting through the baffle and into the carb.

Onto the question - is it possible for me to just ditch the PCV and run that line i have coming out of the fitting in the back of the intake into some sort of oil catch can that I can drain time to time? Which basically just makes the can a breather tank? I think this is basically just the same as having no PCV and just running breathers on both valve covers. I was thinking about mounting an old AC oil filter canister or even a beehive oil filter canister on the firewall and using that as the oil catch can that can be drained every now and then.

 

Here's a photo of the fitting, underside baffle, and the last photo shows the hard line coming out of the fitting behind the carb that runs into the front vacuum port on the Qjet.






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This article talks about exactly what I'm thinking at the very end. The air is being pulled in from my oil fill tube breather cab and exits out of the fitting in the back of my intake into an oil catch can that I can drain every oil change. Any more thoughts or comments appreciated.

http://oppositelock.kinja.com/ditch-that-pcv-system-before-it-is-too-late-1634156554

 

That's a great looking setup. The baffle will do it's job, and the swagelock fitting it a nice easy, clean way to go up top. That will practically disappear under the distributor and behind the carb, and what you do see will be attractive. Nice.

 

Ttt if anyone can chime in


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here´s what I did on a 383 I built for a friend,he is running closed and unvented Edelbrock valve covers. He may have put 50 or 60k miles on it now and didn´t complain yet. s.

 

I've looked into the PCV quite a bit in the past month. I have always run one in the past without any thought and I was going to try and run my sbc without it. You want to run one. Use your can idea as an inline filter. Leave the PCV in place and run the manifold line to the can and run another hose from the can back to the carb. More or less an oil separator in line.

 

My main question is the pcv even necessary? Can't I just vent the back of the intake like the road draft tubes did? Wouldn't this be the same as ditching the pcv, plugging the hole I made in the back of the intake, and just running breathers on the valve covers and keeping the vented oil fill cap? Or is there still not enough air coming in with only a vented oil fill cap?

In my system I'm pulling in air from the oil fill cap and the fitting out of the back of the intake will push a little oil to release any pressure that would be caught in the catch can. There's no vacuum from the carb pulling the air out of the back of the intake, but it's still being vented to release any pressure. I'd prefer not to have that crankcase pressure out of the back of the intake be recirculated back into the carb even with some kind of oil separator. It's just more lines and filters I have to try to run in such a small area behind or under the motor.


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Can you run it that way? Yes. Is it as effective as a PCV? Probably not. The vacuum from the carb draws fresh air in through a vent (oil fill tube) and helps eliminate moisture and all other sorts of "stuff". The way you are talking about setting it up would just allow the motor to "breathe". I see what you are saying about the road draft tube concept in the manifold. I just don't think it would be as effective as the PCV. But, hell, as much as we drive hot rods compared to a daily drivers, it will probably be fine.

 

Right. Yeah if this was a daily driver I wouldn't feel bad for running lines to set up an oil separator before the inline pcv.


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As norcalchris indicated, the pcv does more than just allow the crankcase to breathe. You probably could just go with a catch can as you described, but why? What does it gain you by doing that? You do have to add this catch tank to your firewall or wherever you mount it, and you have to drain it periodically, and the oil will definitely age faster as there won't be a pcv pulling water and other undesirable vapors out of the crankcase, which will cause the oil to degrade faster and could result in increased lacquer and varnish deposits inside the engine. So again, what does it gain you do run it that way, and does that offset the negatives?

 

PCV is positive crankcase ventilation.
You can vent the crankcase in many ways, when you capture the "vented air" it becomes a "positive" system. When you tromp the loud pedal there's no manifold vacuum to capture the offed gasses and vapor however there is a vent that goes to the air cleaner and the stuff is forced thru that vent and then drawn down the throat of the carb.

Elimination of the road draft tube and using vacuum enabled evacuation of moisture from the crank case at start up and eventually eliminated the black strip down the center of road clearly visible in old pictures. It also cleaned up engine bays from stray oil vapor mess.

 

The point of the catch can is to keep any shit from dripping down onto the road or the bias tires. I can mount a catch can under the body along the frame and drain it whenever needed. I'm not driving this car 20k miles a year. Maybe 5k tops. And I plan on changing the oil every season anyways so shorter oil changes isn't a big deal. I don't want to seal the plug up that I drilled in the back of the intake for that pcv fitting because then it'll blow out of the oil fill breather cap. I'd rather it blow out into a controlled situation. I can't imagine it blowing that much out of the tube the little amount I plan on even driving it.


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You could probably stuff a brillow pad into your fabricated vent in the manifold under the swagelock and solve it scavenging oil and draw just vapors.

Study any breather or valve cover baffle and should become clear

 

I completely understand how the baffles work and how they're made but at this point I'm not going to remove the intake to stuff the inside of the baffle. I just needed to make sure doing my initial idea was worth trying.


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Like this?

 

No offense
The dealie you fabed up isn't anything like every other proven design of a properly working baffle. The understanding may be new or have come after the fact, idk? No need to explain that the oil isn't supposed to get to the vent, just the vapors.

Your original idea would work well for $21.10 investment & an hours time.
$20 for gaskets and $0.10 for a brillo pad.

Your catch can idea would work well too, as with any evaporative or ventilation system, it would be powered by pressure differential causing a flow of high pressure into low pressure.
It won't be like a road draft tube though,,,, so how will you power it?

The road draft tube actually pulled a vacuum on the crank case when moving due to Bernoulli's principal. While stationary the road draft tubes blow oily air and suck dirty air as the volume in the crankcase changed from Pistons moving up and down and compression lost. Chevies had a internal baffle that resembles a cross between a soup can and a lawnmower muffler. This let the vapors go out but stopped the oil from escaping and kept it in the crank case as well as prevented contamination from entering.

If you power your catch can with vacuum from that dealie you'll still be sucking oil into it or if you don't power it you'll not have much ventilation

 

I understand the point of the catch can, I asked what benefit does it give you from what you currently have. Right now you have a functioning pcv system evacuating the crankcase gases. It may suck some oil, but it functions. If you disconnect that and change it to you catch can set up you lose the functioning pcv system. What do you gain by making that change? If you're worried about the oil that is being drawn into the intake, how much do you think it is? Are you seeing excessive oil consumption? You didn't even notice it until you tool the carb off. What's the problem you're trying to address, and is it really a problem?