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Early Olds -- PCV Valve Conversion?

Discussion in 'The Hokey Ass Message Board' started by Large_911, Feb 12, 2009.

  1. Large_911
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    Large_911 Member

    I have a 57 Olds 371 and I am thinking about getting rid of the road draft tube, and going w/ a PCV valve. I was thinking of a couple options and I wanted to bounce it off of everyone:

    1) Machine a plate that bolts to the block where the existing road draft tube was and install the PCV valve there. I assuming I would still want to use the baffle that is on the opposite side of the road draft tube under the intake.

    2) Machine a plate and completely block off the hole for the existing road draft tube and just pull from the valve cover.

    Also, I have a buddy w/ a 324 and wants to switch to a PCV valve too; does anyone know if the bolt spacing and hole size in the back of the block is the same for the 324 & 371? If so, I can just make two plates at once.

    Any comments & suggestions would be greatly appreciated! Thanks in advance.

    Chris
  2. Mr48chev
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    Mr48chev
    ALLIANCE MEMBER

    There used to be retrofit kits that just replaced the draft tube. I think you have the right idea with making the plate or just modify the draft tube to be able to fit a pcv valve in it. I've seen that done a lot in the past.
  3. Truckedup
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    Truckedup Member

    I've retfitted PCV systems on several vintage engines, I think it's worth the trouble.On a V-8 I take the easy route,drill the valve covers for a breather and PCV like a later Chevy V-8.If you have nice valvecovers you may not want to do it this way
  4. flatoz
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    flatoz Member

    I was looking at my 324 the other day and noticed it seemed to be 'breathing' a bit heavy from the RDT. I was wondering about doing the same thing, as I have done the conversion on my flathead. I wondered about two ways to do it, there are more but I don't want to drill the valve covers.

    1st was to measure the RDT hole and hopefully find a freeze plug that size, then drill and tap the freeze plug for a PCV valve run the hose to a vacuum port on the adaptor for the holley.

    2nd was a sort of similar thing as what I did with my flathead. that would be cut the RDT about 6" long from the block that is, find a freeze plug that is roughly the right size and then weld/silastic to the open end of the RDT to completely seal it, then get a piece of flat bar and weld to the side of what is left of the RDT then drill and tap that for the PCV valve and run hose to the carb.

    I have done this second one with the flatheads, as on the 8BA motors they have a tube that rises from the sump into the valley, you just cap the open end, weld on a piece of flat bar 1/4" thick will do and then drill and tap for PCV, the beauty with the flathead though is then you drill and tap into the underside of your intake so it all remains hidden in the valley.

    The other reason that I wouldn't go the way of the valve cover PCV is that looking at the manual on how the gases flow through the motor, it would be best to be drawing them from the RDT area, as the flow is all directed to that exit, if you just took the PCV from one valve cover I'm not sure if you would be collecting all the gases? and getting the effect of cleaning the engine which is what your chasing.

    hope this helps, if you dont quite get what I'm saying let me know as I can take photos of what I'm talking about to clarify.
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  5. droplord49
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    droplord49 Member

    On my 324, I went autozone, found a PCV grommet that fit in the road draft tube hole and PCV vavle both hanging on the rack next to the oil filters. Went home, stuck the grommet and valve in the rdt hole, ran the hose to my carb and took her for a spin. Took about 5 minutes and works great(no more smelling like engine breath).
  6. Bobert
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    Bobert Member

    Droplord's set up probably looks something like this. used the oldest Olds pvc I could find.
    Yes, keep the baffle that's inside the valley pan.

    Attached Files:

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    Last edited: Feb 12, 2009
  7. 3x2rocket
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    3x2rocket Member

    Mine worked out exactly like droplord and Bobert's, I had a pcv and grommet laying around and the first one I tried worked perfectly, looks identical to Bobert's pics, 5 minutes.
  8. 61bone
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    61bone Member

    A simple pcv system. Using the draft tube base where it bolts to the block, weld a 1/2" nipple to it in place of the tube that goes down. Or if you want to maintain the look, plug the tube and add the nipple on the other side. Run a line to the inside of the airfilter in the base of the aircleaner. The inlet is the same as it always was, a filtered valve cover or filler tube breather. Doesn't appreciably upset the mixture and keeps the carb shafts lubricated.
  9. Large_911
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    Large_911 Member

    Thanks for the input everyone -- lots of good info! It looks like it may be an easier task then I thought.
  10. Large_911
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    Large_911 Member

    I am going to try to tackle this project this weekend. Would anyone happen to know offhand the ID of the RDT? I like the idea of putting a freeze plug in there, then drilling out for a grommet, or just going with a big grommet to fit in there. Thanks.
  11. r8odecay
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    r8odecay Member


    For my caddy, I took the road draft tube that I cut off after the elbow, took it up to autozone or whatever, and got a pack of assorted PCV grommets...Had to buy the whole pack to get the exact one I wanted, (about 5 dollars) but it was a perfect fit. Put a light smear of black RTV on,and plugged er in.

    NAPA also carries a ton of different sizes of grommets, that you can view online.

    If memory serves the grommet it was 1.25" OD...not sure this applies to your engine, but was a super easy task...
  12. oneqwkfbody
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    oneqwkfbody Member

    Anyone know the rdt diameter on a 303 olds in a 53? Looking to do a pcv conversion tomorrow. And I can just run tue line from the pcv valve intothe airfilter or carb?
  13. porknbeaner
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    porknbeaner Member

    I'll be modifying the road draft tube on my 394 along the lines of what you are considering. Yes you want to use the baffle.

    Another easy approach is to block it off and poke a hole in your valley pan. You'll still need a baffle and I think that the road draft tube is a good way to go with it.
  14. Terrible Tom
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    Terrible Tom Member

    Gonna try it today on my 303 Olds, but man, the bolts on that road draft tube look like a real pisser to get at. Since I don't have a vacuum port in the carb, I think I'll run it into the air cleaner and see how that works.
    Tom
  15. Large_911
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    Large_911 Member

    Hi Tom - Any luck?
  16. Terrible Tom
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    Terrible Tom Member

    No, haven't got to it yet. I have to do all my work outside and the weather wasn't cooperating last week. Maybe this week.
    Tom
  17. BJR
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    BJR Member

    Running it into the air cleaner does not pull enough vacuum to operate the PCV correctly. It must get manifold vacuum. The hose that goes to the air cleaner on newer cars is for the intake of clean air into the crankcase.
  18. Terrible Tom
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    Terrible Tom Member

    I was wondering about that. How about tapping into the manifold then?
    Tom
  19. Terrible Tom
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    Terrible Tom Member

    Can anyone show me where a good spot to tap in would be?
    Tom
  20. BJR
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    BJR Member

    Behind the carb would probably work. See if it goes into both sides of the plenum. You want to pull vacuum from both sides of the carb.
  21. tex1g
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    tex1g Member

    I am looking at doing this conversion on my 1953 this week. Which vacuum line on the 2 bbl carb should be used? There is the line from the front of the carb that goes to the distributor and there is the line that goes from the mechanical fuel pump vacuum to the back of the carb. Any info would be greatly appreciated. :)
  22. Martin_F
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    Martin_F
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    1. The HEAPS - Old Dominion
    2. Virginia HAMB(ers)

    I don't think you'd want to use either of the two lines.
    You are pulling junk out of the engine, so either the vacuum advance or the wipers would quit working over time.
    On my later model 425 I just tapped a hole into the side of the (aluminum) intake and hooked it to that.
  23. PackardV8
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    PackardV8 Member

    Adding a PVC to a carb not originally fitted with one will sometimes FUBAR the idle adjustment. Some carbs have enough air/fuel adjustment to cope, some don't. A 2-bbl may be easier to tune than 2x4bbls, because the curb idle throttle blade openings of 2x4 are cranked down tight. Adding PVC air underneath makes setting A/F problematic.

    Having said that, there are a wide range of PVC valves. Some pass more crankcase air than others. Unfortunately, I've never been able to find a chart which gave CFM@X"vacuum. I've had to try several to find one which worked.

    jack vines
  24. chrisp
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    chrisp Member

    I was wondering about that, if you have a 120ci 4 banger that pumps 80hp or if you have a 394ci 300hp v8 I suppose you don't use the same pcv valve, so how do you select one? As for screwing the adjustments, wouldn't a catch can prevent that or some of it?
  25. Scott De Shields
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    Scott De Shields Member

    Can the PVC hose be tied into the same line coming from the base of the stock 4 barrel carb that also produces vacuum for the power brakes on a 55 Olds?
  26. flatoz
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    flatoz Member


    you dont go into the carby, you go into the intake. either into a plugged port from the factory(dont think there is one) or drill and tap one yourself.

    If your not happy to drill and tap into one of the runners, the easiest way, and how i did it on my 4B is i added a spacer1" or even 1/2" somecome with a vacuum port already there, if not its easy enough to drill and tap yourself. only issue is longer than stock studs, but that is just some 5/16 all tread cut to length. got a photo of my set up if you want to see it. the PCV certainly stopped the motor breathing when at the lights.

    as to PCV selection, any like V8 that the PCV will work for you will do, go to the friendly parts storeand rummage through their stuff or a junk yard for what will work. but suggest buying a new one, their not that much
  27. Barrelnose pickup
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    Barrelnose pickup
    ALLIANCE MEMBER

    I know some have a poppet and light spring in them and others appear to have just a poppet but would a PCV valve work on it's side.I did the draft tube mod and was planning to fit a valve on it's side because of room but am not that sure it would work.
  28. BJR
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    BJR Member

    Yes that is a good place to get the vacuum. Just T into that line. Check to see if it messes with the power brakes. If not, you are good to go.
  29. plymouth1952
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    plymouth1952 Member

    This is what we did before 1966 it works well
    :eek:
  30. ago
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    ago Member

    Any recommendations for PCV part numbers for blown engines.


    Ago

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