Street/Strip Crankcase Vacuum using a PCV Valve

Mopar Racers Forum

  1. weedburner

    weedburner Well-Known Member

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    Here's the evac system I had been using. These valve covers are a circle track design that originally used a crossover tube with a couple small breathers, I eliminated the crossover setup and made some adapters to plumb them into a separator can that I had also installed a pcv valve into. The hose out the bottom is connected to a standpipe inside the separator, other end of that hose connected to the inlet of the electric pump. Outlet of the electric pump had a large header evac style check valve to eliminate the vacuum leak when the pump was not turned on. Using the pcv valve as a crankcase vacuum source worked so well that I rarely turned on the electric pump, got to the point that I considered the electric pump system as dead weight.

    evacpcv1.jpg

    I ended up eliminating the hoses, separator, electric pump, and check valve. I replaced them with a modified version of the original crossover tube. Basically I made some Delrin check ball seats that fit inside the aluminum crossover tube's breather standpipes...


    pcv2b.png
    pcv2c.png

    For the check balls, I bought some 1" dia nylon bearing balls, cost me around $5. I also installed my homemade adjustable pcv valve that had formerly been installed in the separator...

    pcv2d.png

    The plastic elbow on the pcv valve rotates, I pointed it off to the side and attached it to it's hose.

    pcv2e.png

    These check balls are pretty light-weight, launching the car does not cause them to become un-seated and leak crankcase vacuum.

    Grant
     
    Last edited: Jun 9, 2021
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    • 512Stroker

      512Stroker We are all here because we are not all there.

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      Nice!
      That first set up looks like it could suck a golf ball thru a garden hose.
       
    • 512Stroker

      512Stroker We are all here because we are not all there.

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      These check balls are pretty light-weight, launching the car does not cause them to become un-seated and leak crankcase vacuum.

      "Crankcase vacuum"
      Do you run a vacuum pump?
      Most crankcases run at slight pressure even with a PCV
       
    • yellow rose

      yellow rose Overnight Sensation FABO Gold Member

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      Interesting. So at high vacuum the balls cover the breather holes and at low vacuum the balls get out of the way and let crankcase pressure out of the breathers. Am I getting that right???

      So no vacuum pump either? I’d like to test all that on a dyno and see what happens.
       
    • weedburner

      weedburner Well-Known Member

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      No vacuum pump at all with the 2nd picture setup, just a pcv valve sucking against a sealed crankcase. Crankcase vacuum is essential for my low tension rings on the street, an earlier version of this engine only got around 250mi to the quart before I sealed it's crankcase and added the pcv valve.

      The pcv valve has been modified to make it work similar to adjustable orifice, currently set to draw around 12-15"Hg in the crankcase while cruising down the highway. Here's a RacePak graph showing crankcase vacuum during a 6.25sec long WOT 3rd gear pull with the pcv valve as the only vacuum source. Nitrous system was NOT turned on, this pull was NA.
      ...Red line- engine rpm
      ...Blue line- WOT switch
      ...Yellow line- crankcase vacuum

      shopmulepcvonly.jpg

      The pull started out with 12.6"Hg @ 2600rpm. When the pull ended at 6250rpm, even without the electric pump running the crankcase still had 3.9"Hg of vacuum left. I should add that the 355" engine is well sealed, no dipstick (oil level sight glass), Total Seal gapless top rings, and a 114 LSA nitrous cam.

      When blowby exceeds the volume of the pcv, the check valves un-seat and any pressure is vented thru the breathers.

      Grant
       
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      • weedburner

        weedburner Well-Known Member

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        You got it right. The version before this had an electric vacuum pump as backup, but I rarely needed it. Decided to cut the extra weight and let the breathers be the relief.

        Grant
         
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        • 512Stroker

          512Stroker We are all here because we are not all there.

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          Dam Boy
          We need to change your handle to - Professor Vacuum
          Nice job
           
        • weedburner

          weedburner Well-Known Member

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          It would be a lot of work to verify the benefits on a dyno, as the main benefit to me is being able to run lighter tension ring packs on the street. It's part of what helps me net 20mpg on the highway without an overdrive, not to mention less wear/tear on the cylinder walls. Easier to cool the engine too. I'm 3100rpm @ 70mph.

          Grant
           
        • 512Stroker

          512Stroker We are all here because we are not all there.

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          20 mpg - nice
          But I am from MO you offer up a statement like that and you are going to have to show me some proof.
           
        • weedburner

          weedburner Well-Known Member

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          Mileage was calculated using a gps tracking app on my phone, never bothered to hook up the speedo. Car is currently 2300lbs, 4spd manual, on radials with fairly good aero. TruTrac diff allows it to roll pretty free thru the corners. Low compression pump gas engine with nitrous, it'll also do 70mph in 1st gear :) Here's a link to the car's build page- http://grannys.tripod.com/20102.html

          Grant
           
        • 512Stroker

          512Stroker We are all here because we are not all there.

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          What the hell kinda A body is that!
          Cant say that I am familiar with that one.
           
        • LO23M8B

          LO23M8B Well-Known Member

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          Hi there. Very Very nice! What's the name of your shop?
           
        • yellow rose

          yellow rose Overnight Sensation FABO Gold Member

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          I was talking about monitoring crank case vacuum, but I forgot you are data logging.
           
        • LO23M8B

          LO23M8B Well-Known Member

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          Ya data is the key. Lots of $$$.
           
        • weedburner

          weedburner Well-Known Member

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          Just sharing the breather/checkvalve thing, might work on an A-body too. For some Mopar content in this thread, here's a pic of a naked dirt latemodel I built back in the late '80's...

          latemodel3a.jpg

          Won a few features, at the time it was the only Mopar at the track. The engine was a 440 BBM that was mounted backwards in the car. The homemade transmission's input shaft plugged into a hub that bolted onto the engine's damper. Backwards engine meant that the drivetrain spun backwards. Quickchange was modified to flip the spool, putting the ring gear on the other side of the pinion.

          The car after that one was powered by a homemade 4 rotor rotary engine, it's what originally got me into the Mazda. Here's a link to that car's page and info, you will find the Mopar car at the bottom- https://grannys.tripod.com/4rotor.html

          Grant
           
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          • weedburner

            weedburner Well-Known Member

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            Granny's Speed Shop. I used to manufacture V8 conversion kits for Mazda RX-7's, now I make my ClutchTamer and Hitmaster products.

            Grant
             
          • justinp61

            justinp61 Well-Known Member

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            Looks like a nice built small block Chevy.
             
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