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Road Draft v. PCV

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  • Road Draft v. PCV

    My '61 390FE has a Road Draft Tube, and I assume this is in place instead of a more traditional PCV for this 390FE.

    It seems the only serviceable part is replacing the oil filler cap, where the filter in its intake is very, very dirty. The Shop Manual talks about both,'s not clear to me.

    I am seeing smoke from the Road Draft Tube at when idling hot. I cannot judge if its excessive or not, because I don't know what it the norm.

    If I replace the oil filler cap with a clean one, does that help? Also, should I consider a conversion to PCV? If so, how difficult and expensive is that? Is there really any reason to do a conversion?
    Last edited by GeoffInCarlsbad; October 11th, 2015, 10:51 AM.
    Geoff In Carlsbad
    1961 Thunderbird Convertible aka: Betty:cool:


  • #2
    Conversion will eliminate the smoke, fumes, smell and drips to the outside. A PCV system will not keep these emissions from happening, just return them to combustion chamber. Definitely a "must do" in my book (I did it to my 57 Y-Block).


    • #3
      X2 with Joe.

      The new clean cap "should" allow more air into the crankcase and actually increase the amount of smoke out of the road draft tube.

      On my original 352 (road draft) I tried plumbing the road draft tube to the air cleaner in hopes of returning the smoke and fumes to the combustion chamber. It worked but at idle there was not enough vacuum to pull all the fumes out of the crankcase into the air cleaner so still had a little out of the oil filler cap. Also tried a different oil filler cap with a vent tube and plumbed that to the same point on the air cleaner which helped but since the caps are push on style and not sealed it still puffed a little smoke at idle out of the cap.

      My original 352 finally called it quits so I replaced it with a 390.

      That replacement 390 did not have the oil filler neck in the intake so I changed to chrome valve covers with holes (and some 312 valve cover stickers ). Bought one of the carb spacers that has PCV input. One hole in the valve covers I use as the oil fill and PCV filter cap the other I installed a PCV grommet and valve. Ran the PCV output to the carb spacer input.

      Works nicely.


      (sorry about the small pics - dropshots wont let me access my full size pics at the moment, Hopefully the description works. Never use dropshots for pics - they are the worst pile of you know what)

      Think the 61-63 Tbird PCV carb spacer (or maybe later) had this style spacer which also has provision for coolant to keep the mixture at a constant temp but I didn't use that style.

      I used this style but don't know what it came from. 428? 429? There are also 2 types of this style - draws from different holes so need to make sure your PCV draws from the primary not the secondary ports.


      • #4
        If your rings are so badly worn that they produce copious amounts of stink, NO PCV system will work completely. You will need an engine overhaul.

        There are two basic types of PCV, passive and active. Back in '61 nobody took crankcase ventilation seriously.

        The first systems brought the 'draft tube' to the air cleaner for recycling. Of course, this was installed on new engines.

        Y-Blocks depend on this crankcase 'smoke' to oil the timing chain set UNLESS you incorporated serious oil modifications in your overhaul.

        Active PCV uses a special PCV Valve to stop carb backfire from injecting fuel mixture into your crankcase if your car backfires. This valve is a CHECK VALVE in one direction and it limits flow in the other direction. All this is accomplished by use of a 'prindle' and spring inside the valve. DO NOT pipe a hose from your intake to your crankcase without a PCV Valve.

        There are many PCV systems on the internet. I suggest you learn what's best for your engine because there is a lot to this. - Dave
        My latest project:
        CLICK HERE to see my custom hydraulic roller 390 FE build.

        "We've got to pause and ask ourselves: How much clean air do we need?"
        --Lee Iacocca

        From: Royal Oak, Michigan


        • #5
          Thanks, men.

          Hi Eric, Dave, Joe:

          Thanks for the info. I think when I reseat and seal my intake manifold, I am going to install some form of PCV. The information provided is great, and I'll do some additional research.
          Geoff In Carlsbad
          1961 Thunderbird Convertible aka: Betty:cool:



          • #6
            Slightly better pics

            Know you said you were going to check but if you go the carb spacer route check to see if you need a flat style (similar to the silver one) or an angled/tapered style like the brown one. The 58-60 Squarebird engine sits at an angle so you need the angled or tapered brown style.

            This pic was during my engine swap and I was trying the flat (silver) style. Realized it wouldn't work after buying new longer carb studs etc. That's when I switched to the chrome valve covers and tapered carb spacer.

            Good luck with your PCV project - your blue convertible looks sharp.



            • #7
              Great a few newbie questions...

              HI Eric:

              Thanks for those pics. I am posting a few back because I have just a couple of questions about them. If you click on the images, they will come up full size. I have not mastered how to make them appear larger on the post.

              1) Did you have a Road Draft tube or was there already some PCV in place?

              2) Did you run the PCV from the spacer to the valve cover on the other side? I love the chromed valve covers! It would be interesting to see how this looks under the air filter cover.

              3) Was this simply what you did before painting and new chrome? Also, this insulated tube hangs down on the passenger side as well. I thought this was a hot-air/pcv return that needed to be fed into the exhaust manifold? But I have seen other vehicles where it just hangs down as well....but the manual is not clear or mentions much about this. Are you feeding it back to the exhaust manifold?

              So on my 390, the Road Draft Tube exit out of the back of the Intake Manifold. Would I simply re-route that back to the valve cover with a PCV valve on it?
              Geoff In Carlsbad
              1961 Thunderbird Convertible aka: Betty:cool:



              • #8
                Your pics are fine - mine are probably too big but I'm having issues with my photo hosting site - dropshots.

                Yes those pics are reversed and as you noticed the '60 Tbird hood opens forward.

                In question #1 - that probably looks like the old engine with those crummy blue valve covers but it is actually the newer ('64ish) 390. It came with that silver carb spacer for PCV so I tried to use it. There was no road draft tube on this engine. I had planned on using the PCV style blue valve covers (but would paint them yellow as was original on the '60/352). Didn't like them and decided to go with Chrome. I bought the Chrome ones off ebay for about $35 new (for both!). Not show quality around the edges but good enough for my driver. Would have used my original yellow valve covers but they do not have PCV or oil filler ports and I would have had to cut holes in them.

                #2 Yes - you can see the 90 deg PCV valve in the valve cover - it comes out to a hose that is piped to the carb spacer vacuum input. On the other valve cover I have a different grommet in the valve cover for a filter cap which is my fresh air intake for the PCV system. As a bonus the filter cap is removable so I can add oil here since the 390 intake did not come with a filler port like on the old 352.

                I'm using this style push in chrome filter.

                Don't have a pic under the air cleaner at the moment - sorry.

                The valve covers came with little push in filters but I didn't like them. Here's how they looked before I installed the PCV valve. This would supposedly filter the air entering and leaving the engine.

                #3 - yes that was my set-up before switching to PCV. You can see where I piped the road draft tube to a T and then using a oil filler cap with a tube port I ran it to the other side of the T. That T then was connected to the air cleaner to supposedly re-burn the fumes (that was my theory anyway). May have worked better if I had piped them both to the carb vacuum input through an in line PCV valve rather than to the air cleaner but the engine failed before I got to that stage.

                Used this type oil filler cap with filter and PCV connector on that set up.

                That style setup usually works in the opposite way I tried to use it which is why it probably didn't work so well. The connection to the air cleaner is usually the clean air intake for the PCV system eliminating the need for a filtered oil filler cap. You would have to run a tube from the air cleaner to one valve cover for the filtered air input to the engine. Out of the opposite valve cover you would have your output running through a PCV valve to the carb plate or intake vacuum port.
                That would make the assumption that the fresh air from one valve cover would make it through the engine to the other side to be pulled out by the vacuum.

                The other smaller pipe covered by the heat shield cloth goes to the carb and is the hot air intake. When the car warms up the hot air through the tube will cut the choke off as the hot air enters the choke mechanism.

                Hope that helps.
                No problem on the ?'s that's what this site is all about.



                • #9
                  Great! Thanks!

                  Hi Erik:

                  Thanks! I think I have the idea now.

                  Geoff In Carlsbad
                  1961 Thunderbird Convertible aka: Betty:cool:



                  • #10
                    Shop Manual Diagrams and Intake Manifold

                    Looking at the Shop Manual, page 1-21, Figure 30, here is what the PCV (Crankcase Ventilation) should look like on the 1961 390 FE. (Click on images to enlarge).

                    A top view on page 1/23 Figure 32 looks like this:

                    On my 1961 Betty Bird, I have a Vacuum Exhaust Pump Connection (bolt) sitting in the Vacuum Pump Connection, nothing attached.

                    Right now, I have the Road Draft Tube coming from the Crankcase Ventilation Outlet.

                    So here's the question: Are there any reasons why I cannot convert the Road Draft Tube to the PCV as described in the shop manual? I suspect I can buy the correct parts, though I am having trouble with the Vacuum Pump Exhaust Tube Connection. No one seems to have that.
                    Geoff In Carlsbad
                    1961 Thunderbird Convertible aka: Betty:cool:



                    • #11
                      Where the bolt is on your intake my '60 had a dual port adapter. One port went to the vacuum assist fuel pump (basically a booster for the vacuum wipers from the engine intake) - the other port to the vacuum booster for the brakes.

                      Carl Heller ( partsetal ) here on the forum should have a used adapter.

                      When I installed the '64ish engine that port had been moved to the back corner near where the road draft tube was. Found a pic! (carb was covered with plastic wrap to keep out any loose stuff that would have surely gone into the engine if I hadn't covered it).

                      First off - you can see the PCV cap in the valve cover that I described earlier (acts as the crankcase breather and the fresh air intake for my PCV). Since it's a push in style that's where I add oil. Yours still has the oil fill at the crankcase so you will need the style filter cap that pushes in to the breather tube. Believe you already have that but were going to get a new one. That's where I still had a little smoke coming out on my first PCV design try.

                      Plumbing nightmare - but on mine you can see the rubber hose attached to the back of the carb spacer (PCV input) then connects to a hard silver metal tube that I ran beside the valve cover and across in front of the carb to another rubber hose which connects to the PCV valve on in the other valve cover. You shouldn't need any of that for your original style system.
                      The rest of the silver metal tubes are for the vacuum wipers and vacuum to the brake booster.

                      Don't see any reason you shouldn't be able to use the original PCV system. Might be a little hard to find that crankcase vent outlet adapter too but I just took the road draft tube off my outlet and used that smaller opening. As Dave mentioned if the engine is really worn it may not grab all the fumes but I figured some was better than none.

                      I wonder if that regulator valve is actually regulating the amount of vacuum being pulled too and not just a PCV valve. Carl will know and may have one of those as well.

                      One of these may be the type PCV/regulator you need - guess you would need to find the original part number and cross reference.



                      NAPA might still carry them if you can get the part number.



                      • #12
                        What size steel tubing did you use?

                        Ok, I have collected up all the parts I need except for the steel tubing to run from the Vacuum Pump Exhaust Tube Connection to the PCV Regulator.

                        What size steel tubing do you recommend? 3/8"? 1/2"? 5/8"? It has to be big enough for the PCV to get through.....

                        Geoff In Carlsbad
                        1961 Thunderbird Convertible aka: Betty:cool:



                        • #13
                          Unfortunately the Ford Parts manual doesn't show the size of the tube. However the tube connector shows a 3/4"-18 fitting size so it appears to be larger than 3/8"

                          John Pizzi - Squarebirds Administrator

                          Thunderbird Registry #36223



                          • #14
                            thanks John!

                            Hi John:

                            Thanks! Yes, the manual is somewhat remiss about some of these specs. I'll probably go 5/8" if I can. The local restoration spot recommended that size or bigger to accommodate the PCV.
                            Geoff In Carlsbad
                            1961 Thunderbird Convertible aka: Betty:cool:



                            • #15
                              For the PCV lines shown - I used 5/16 fuel line I had left over (I replaced the fuel line on my car a while back and it was laying around) seems to be working fine but a little larger probably wouldn't hurt. I think the PCV inlet was around 5/16 so figured if that was a large enough opening for the valve it should work for the line - but I was definitely guessing (and besides - the fuel line was free so that made it even better).

                              I bought a used vacuum line from Carl for the brakes - not sure what size it is (didn't want to modify my original). To make the used line that I bought from Carl reach to the other side of the block where the new vacuum port is I put 5/16 line inside the used line and soldered them together. Of course that tells us that the original brake vac line is a little bigger than 5/16.