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Technical BLOWN FLATHEAD PCV QUESTION (RETROFIT)

Discussion in 'The Hokey Ass Message Board' started by Bandit Billy, Jul 29, 2020.

  1. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 7,050

    Bandit Billy
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    Let me begin by saying I love this flathead! It is faster than I expected and drippier than I wanted. On the latter point, I erred I believe in not pursuing a positive crankcase ventilation system. I added a breather to the rear of the intake and another in the top of the oil pan, visible barely in the picture below. But the issue is the oil pan breather is leaving a light oil spray all the way to the back axle. The benefit is all of the chrome and polished stainless under the car will never rust but the clean up is a bit of a bother. This wasn't an issue during break in but now that I am driving it harder it is getting proportionately harder to keep up with the detailing.
    upload_2020-7-29_10-33-19.png
    Also identified above is the carb adapter atop the 471 and the subject of my inquiry. Could I remove, drill and tap the carb adapter/spacer for manifold vacuum? The issue with tapping the intake itself is it is is extremely "busy" and cramped and there are not a lot of options to tap an adequate vacuum source. Perhaps it is not advisable to run the engine gasses through the blower? I do not know so I turn to those who may.

    Here is better view of the adapter/spacer from an old photo. You can see it has plenty of room, I would imagine optimally I would aim at the area directly beneath the center (primary) carb. It would have to be off the right side (shown) as the fuel rail is attached to the same spot on the left-hand side.
    upload_2020-7-29_10-20-43.png
    I have purchased a PCV valve (below) that fits the front draft tube location in the intake that I found referenced on a thread on FB (Ford Barn not Facebook, pulease). I would plumb it with proper (polished) fittings and line of course.
    upload_2020-7-29_10-52-56.png
    Sooo, the inevitable questions to the forum members (hopefully not clad in togas);
    1. Do I tap the adapter for vacuum?
    2. Should I block the oil pan breather or leave it open after installing the PCV?
    3. Would it better to tap a source below the blower for vacuum?
    4. If so, the easiest place without disassembly, is the pop-off plates on either side of the intake (easily visible in the second photo above). I already tapped the right pop-off plate for the vacuum trigger needed for the MSD BTM-6 box. I could remove and tap the opposite side for the vacuum source. The PCV is a one way valve so if an intake backfire were to occur the valve would prevent blowing back into the crankcase correct? This would be the most inconspicuous approach.
    5. If I leave the oil pan breather will it introduce dirty air to the crankcase? Currently it expels air.
    6. Is running the crankcase gasses back through the blower a potential issue as I raised in the text above? I can't imagine since most PCV's are run into carb bases above the blower, this isn't any different really...I think.
    7. Should I ignore the issue and just park the car on a piece of cardboard and wipe it down once a month?

    I have seen others of you run oil pan breathers on your flatheads, perhaps you can tell me if you have similar issues.

    Any better ideas? I am open to hearing other options (other than installing a SBC DDDenny! :cool:).

    Feel free to provide an answer or an opinion to any or all of the above queries. Your responses will not be graded but may be subject to harassment and/or ridicule as per HAMB customary rules of conduct. BB
     
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  2. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,253

    Jmountainjr
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    A PVC system is a good idea. And they usually use carb or manifold vac. You will get constant vac under the carb caused by the blower, not manifold vac. I would tap into the blower manifold under the blower.
     
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  3. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 7,050

    Bandit Billy
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    Ok, so what about this location in the left hand pop-off valve. It would be a short run to the road draft hole and PCV valve. Practically invisible and done in a matter in of minutes.
    upload_2020-7-29_11-59-45.png
     
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  4. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,253

    Jmountainjr
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    Well, it gets you into the right area. It would not be my first choice, but with the engine all together it's worth a try. Chances are you won't pop off the blow off anyway. So you will use the road draft location as the PVC pull location. Where are you getting the air in? The pan breather?
     
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  5. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 7,050

    Bandit Billy
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    There is currently a breather in the rear of the intake (the old fuel pump location) and the pan breather.

    If I use solely utilize the rear intake breather I think the effects of the PCV will be somewhat compromised. It will simply suck the air from beneath the intake, possibly not effecting the crankcase pressure. If I am thinking about it correctly.

    If I close the rear intake breather and solely utilize the oil pan breather on the other hand, I would provide the required result, correct? The only issue then being the air intake is potentially dirtier from that location.
     
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  6. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,253

    Jmountainjr
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    If you used the intake breather, how far away would the PCV connection be? The typical OHV setup is air in one valve cover and the PCV on the other. I would be inclined to try it first with the pan blocked and use the intake manifold breather as the air in location. It should pull enough to take care of things.
     
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  7. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,253

    Jmountainjr
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    Do you know at what RPM you transition from manifold vac to manifold boost? That will determine how much of the time the PCV will work. If it's not enough, I guess you might want to try constant vac. But I would try the manifold vac first.
     
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  8. DDDenny
    Joined: Feb 6, 2015
    Posts: 14,080

    DDDenny
    Member
    from oregon

    :eek:
    I almost swallowed my Three Musketeers bar whole when I found that line hidden in there Bill.
    You know, I'm not a flatty follower so I generally don't even venture there let alone slog through the whole post but be'ins it was you and I was bored (waiting for Judge Judy).
    What was the question?
     
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  9. squirrel
    Joined: Sep 23, 2004
    Posts: 47,179

    squirrel
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    I've always run pcv from the base of a carb on my blower motors. When you get into boost, and you really need crankcase ventilation, what happens if the PCV is connected to the manifold, which is now pressurized?
     
  10. TCTND
    Joined: Dec 27, 2019
    Posts: 171

    TCTND
    Member

    I would tap in beneath a carb, where there will always be some vacuum. The fresh air source can be plumbed into whatever air filter you are (I assume) running. With that setup, if the crankcase sees pressure as it might under load, the excess fumes will be drawn into the intake and burned. This is how a normal PCV system works.
     
    Last edited: Jul 29, 2020
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  11. alchemy
    Joined: Sep 27, 2002
    Posts: 16,090

    alchemy
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    Isn't the intake under pressure at all times? So connecting there would actually push new fuel/air mix into the crankcase (yeah I know it's supposed to be a one-way valve, but it could fail).

    I also have a breather on the side of my flatty's pan. And I also have a well-oiled underside of my car. Maybe I need a blower and a PCV valve too.
     
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  12. Jmountainjr
    Joined: Dec 29, 2006
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    I would listen to Squirrel. I guess tapping the carb adapter is easier than messing with a carb base on the 97s.
     
  13. squirrel
    Joined: Sep 23, 2004
    Posts: 47,179

    squirrel
    Member

    It's under more pressure than above the blower, but still it's vacuum under almost all driving conditions. Roots blowers don't make boost until there's enough air, which means you have to open the throttle a ways. At cruising conditions, you'll see perhaps half the vacuum under the blower as you see above it.

    Keep in mind that atmospheric pressure is 14.7 psi or less (depending on elevation, weather, etc). Partial vacuum is still pressure, compared to a total vacuum. Understand the difference between gauge pressure, and absolute pressure.
     
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  14. seb fontana
    Joined: Sep 1, 2005
    Posts: 6,711

    seb fontana
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    from ct

    ^^^^X2^^^^
     
  15. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 7,050

    Bandit Billy
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    That there we call an "Easter Egg"'buddy. You found it!

    I'll get back to everyone when I get back to my computer. Too hard to read and type on my phone. Thanks fur the triples
     
  16. jaracer
    Joined: Oct 4, 2008
    Posts: 606

    jaracer
    Member

    You could also run hoses from your breathers into the exhaust with some one way valves like Chrysler used to use on their air pump systems.
     
  17. squirrel
    Joined: Sep 23, 2004
    Posts: 47,179

    squirrel
    Member

    I'm running a funky setup on my 427...PCV valve in one valve cover, connected to the base of a carb, above the blower. Header evac system on the other side. Works fine.
     
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  18. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 7,050

    Bandit Billy
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    Okay, back in front of a computer and back to work.
    These are some great responses! I asked Clive if there were any such bases for 97's and there are not. They do not make bases with vacuum ports below the blades. So...that means the two alternatives I described above. Either tap the adapter or below the blower. The adapter seems to be the best idea on this configuration.

    I do not have a boost gauge on the dash but from running other roots style blowers I'd say under heavy pedal and in excess of 3500 on the flatty judging from feel only. I may be off (wife says so) but I bet I am close.

    Sir, everyone does! Blower that is. Perhaps the same is true of the PCV, that is what we are tying to determine. :cool:

    So, the consensus is to tap the carb adapter for the vacuum source and we apparently in agreement (or as close as the HAMB gets to a quorum). Now, as far as intake is concerned? Oil pan breather? Intake breather? Both?

    The distance on a 8BA is the length of the intake. The road draft tube is at the prow and the breather is aft. 8 cylinders and less than 3 feet lie between.

    I have thought about this already. Running a PCV off the oil pan breather (closing the breather holes) into the header and a PCV in the road draft hole venting off the rear breather, a combined effort. It would require re-ceramic coating the left header (after welding in a bung) and some aluminum welding on the breather for the PCV valve but it could be done easy enough (no major disassembly, limited down time, little expense).

    @squirrel , if it was your call would you have me start with the carb adapter and intake valve OR go pan breather and header evac to start with and a possible cure? After all, the issue is the oil pan breather spewing oil about. Maybe direct my attention there? This would look better than a vacuum line to my carb adapter up the side of the blower BTW. That header collector is mere inches away from that breather.

    I may have already answered my question. ;) As well as @alchemy 's
     
  19. squirrel
    Joined: Sep 23, 2004
    Posts: 47,179

    squirrel
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    I don't know what they have for baffling in the pan breather on those engines.
     
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  20. Bandit Billy
    Joined: Sep 16, 2014
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    Neither do I exactly. This is an Offy piece, made for a HEMI valve cover. I drilled a small series of holes in the pan as high as I could toward the rail. I think 3 or 4 small holes, less than 1/4" per as memory serves. I welded nuts in-side the pan to make the breather easy to remove. I figure I would pull the header and breather. Bandsaw the top off the breather (non serviceable) I could create a baffle for the PCV, weld in a threaded bung (too hot down there for a rubber grommet) block the venting to the atmosphere and TIG it back together. A little time on the polishing wheel and back on it goes.
     
  21. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,253

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    As to venting the pan into a header evacuation bung, if it was mine I would need to think about that as it's currently configured. Based on the amount of oil you seem to be getting, my guess is that there isn't any specific baffling in the pan where you have the breather. You didn't mention what, if any, type of material that is in the pan breather. I would be concerned about pulling your current amount of oil mist out of the pan where it's still whipped by windage directly into the hot header. I have run valve cover evacs into the headers, but the volume of oil suspended in the mist seems less on the top end. But I have been known to over think things.
     
  22. squirrel
    Joined: Sep 23, 2004
    Posts: 47,179

    squirrel
    Member

    Stock baffling usually works pretty well, and aftermarket covers, pans, etc generally are not designed to work with stock baffling, and tend to blow oil all over. This is a general statement, not a flathead specific one.

    I'd probably work on the baffling before trying other stuff.
     
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  23. blowby
    Joined: Dec 27, 2012
    Posts: 7,073

    blowby
    Member
    from Nicasio Ca

    On my blown V8-60 I put the valve in the old RDT port in the intake manifold, vacuum above the blower, breather in the oil filler cap at the other end of the intake and blocked off the pan breather. Seems to work but probably better if it circulated through the lower end.
     
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  24. loudbang
    Joined: Jul 23, 2013
    Posts: 31,567

    loudbang
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    Or you could connect a catch can from the breather. That way all that nasty blowby would end up in the can and not all over the bottom of the car.

    Of course that would necessitate emptying the can manually every so often. :)
     
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  25. jimmy six
    Joined: Mar 21, 2006
    Posts: 7,689

    jimmy six
    Member

    If you use the pan vent, you need to baffle it in a way not to suck oil up to the plate below the carbs, may not anyway because it’s a vertical climb.

    If the oil vent at the rear on the intake is physically open to the internals of the engine then the PCV system would not know or care. Think of your SBC; breather on one valve cover and valve on the other and it gets all the vapors your trying to trap from the engine. If you use the rear vent just put a solid gasket behind your pan vent.

    I run a belt driven vacuum pump on my race engine. The suction is at the top of the rocker cover. The vacuum gauge is connected to a fitting on the pan and reads 9” of vacuum during the run at El Mirage. The vacuum is consistent thru the entire engine thru internal venting passages.

    Beautiful Engine...
     
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  26. Bandit Billy
    Joined: Sep 16, 2014
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    Bandit Billy
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    I did mention that I have no idea what is in that breather on the pan, I wont know unless I cut it open as it is non serviceable as in the top does not come off. I do respect the thought that I don't want to inject oil into a red hot header. That is why I post these things and not just go with my ideas. I'm creative and I can build things and that sometimes makes for a messy situation. And it is expensive! (sorry for starting that last sentence with a conjunction)

    I am beginning to think this is a better idea and block that lower oil sprayer, I mean breather. I

    Maybe I could rig up a way to pump the catch can contents back into the pan? :D A perpetual oiling apparatus.

    Thanks @jimmy six It twist the slicks and climbs to 70 in short order but that kind of RPM is what is throwing oil all about. Part of building cars is working out the bugs from your build.

    That is interesting about the vacuum gauge on your pan pulling 9" of vacuum with the breather in the rocker cover. Do you know how much vacuum is being produced by the pump?
     

    Attached Files:

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  27. Billy this is just a thought that ran through my head. If you are using the vac created above the blower for a PCV vac point you may need a PCV that is designed for pretty heavy vacuum. Or you may have to plumb a restrictor of some sort.

    my second thought is that if I were going to add a PCV I would add it to the manifold location and not the pan location so as not to put myself in danger of sucking the pan dry.

    You will sort it our I know that you will but these are my thoughts anyway.
     
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  28. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 7,050

    Bandit Billy
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    Again, had not thought of that. More to consider. Much easier to include this off the gate during your flathead build than retrofitting it later for those of you about to build one.
     
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  29. acme30
    Joined: Jun 13, 2011
    Posts: 175

    acme30
    Member
    from Australia

    If I understand the theory correctly and you have the rear intake breather and you put the PCV valve in place of the road draft tube then the way that the breather and breathing will work on an 8BA flathead is that the fresh air comes in from the rear breather and out via the PCV vacuum.

    Under the manifold
    where the road draft tube goes in /comes out there is tube that goes down into the block with the effect that the road draft tube draws air in from the back of the block, pulls it down underneath the pistons and crank, then vents it out the road draft tube.

    As long as the internal tube is in place the air to the PCV is not coming directly from the valley.
     
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  30. You could go totally modern and install a vacuum pump. LOL
     
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