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do YOU know why this breather set up killed my power??

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  • do YOU know why this breather set up killed my power??

    I'm a bit confused by this and figured there are plenty of smarter people than I who might be able to shed some light on a situation I ran into today.

    It is a 180sx, original motor, with most of the original emissions stuff intact. Still runs .5bar boost (~7 psi).

    the valve cover has a pcv on the back right corner and another T breather on the middle left. I've seen others with just an angle fitting, so I'm not sure if the T is stock, but it appears as such.
    It is missing the crankcase breather can (separator I believe)

    When I got the car, it had a hose running from the crankcase to the T on the left side of the valve cover, and the other side of the T went to the intake upstream of the turbo.

    A few years back I ran the hose to a catch can with a filter on it, and plugged the intake hole, and it ran fine.

    About a year ago I popped the dipstick off after a run, and it kept popping out. A new oring didn't help, so I just ziptied it down, thinking it might be excessive blow by.

    Recently I thought I'd take a better look, and realized that if the pcv valve was malfunctioning (ie letting boost get by it) it could pressurize the motor and potentially cause my popping dipstick (that's the name of my next band I think. anyway...)

    So I blew in the hose attached to the pcv valve and I could indeed force air past it. not super easily, but since I figured i could only generate about 2.5psi, almost 3x what I was blowing could end up giving me the problems I've been having.

    So I ran a hose from the pcv to another t in my hose right before the catch can and just plugged the hose going into the intake manifold that the pcv originally went to.


    Cut to this morning, first time with this mod (and some others), and the car was significantly down on power. It still was boosing .5bar but on was a little slower to rev and just kept bogging. It felt like the wastegate was open or something similar.

    I reversed my breather change and put it back to how it was before and the car was 100%.

    Why???

    here is a horrible pic of the mod before I put it back. it's hard to see, but the shiny spot off of the [car's] left front corner of the valve cover is the new T, with a hose running from there around and back to the pcv valve.

    the light spot next to the "N" in nissan on the valve cover is the tube that the pcv valve goes to that I plugged up.

    Would love some insight...



    side view

  • #2
    You need to put a new pcv valve in (it's like $7 from a parts store... get one for a 91 SE-R sentra) and plumb it back to the intake manifold. You need vacuum under none-boost conditions. Also, you need to keep a vacuum source on the engine under boost, which is what the line between the intake tube and front "t" is for. The line between the T and the block itself needs an air/oil separator, otherwise you'll get tons of oil in your intake and intercooler setup. It's best to run a catch can between the intake tube and the front side of the "t" as well, to keep things cleaner. The car will seem underpowered when there is a bunch of pressure built up in the block. Also the reason why the dipstick is blowing out.

    www.2LiterTurbo.com (Personal Site)
    96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

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    • #3
      I capped my Pcv valve on my SR and it ran fine. But the stock breather from the valve cover has a tiny restrictor in it. I ran a -8 an line and it was much better (to the intake still with a catch can in line).
      '18 Chevrolet Volt - Electric fun hatch for DD duty!


      DefSport Koni Sleeve and Spring Perch Buy!!!
      http://www.nissanroadracing.com/showthread.php?t=5902

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      • #4
        That's good to know about the restrictor. I'm guessing that my problem was not that I capped the intake manifold tube but related to running all three (pcv, vc breather and crankcase breather) into one tube.

        I have no real problem with oil accumulation (an oz or so after 1000 track miles) so not having the stock separator doesn't seem to be an issue.

        I could run my catch can breather to the intake pre-turbo which would help scavenging (great) but introduce "dirty" air into the system (bad).

        After seeing how much power I lost with a poor routing, I wonder if there is power to be made by applying a vacuum to the crankcase.

        I guess the two theories I'm playing with are:
        A. Venting everything to atmosphere and maybe even adding ports. This would ensure that the crankcase and valve cover do not see any positive pressure.

        It would be fairly clean and easy, just necessitating another catch can an possibly more breathers.

        Or
        B. running an electric or mechanical air pump to apply constant vacuum without contaminating the intake. More complex and heavier.

        My two questions with this are, 1 would it be better to apply vacuum to the crankcase only or vc as well? They're obviously connected so I assume both would be best.
        And 2 would it be better than a super ventilated motor or the same?

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        • #5
          They're connected, you just want a vacuum in the engine overall as there are BIG areas like the front cover connecting them. The beneficial part of the vacuum is in the crankcase on the rings.

          Pumps work well until they die. I think Terminator Cobras had a vacuum pump stock that people use, but it's pricey, and does not tolerate much oil vapor. You can also use the exhaust to pull a vac, but it's load and back pressure dependent, plus it can fill your exhaust with oil vapor.

          The intake isn't too bad if you don't have much blowby and run a catch can in line to catch junk. I would get just a light mist just downstream of the turbo, and a more sticky gunky mess in the intake pipe that I'd just clean every few months. No big deal really.
          '18 Chevrolet Volt - Electric fun hatch for DD duty!


          DefSport Koni Sleeve and Spring Perch Buy!!!
          http://www.nissanroadracing.com/showthread.php?t=5902

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          • #6
            The PCV valve plumbed in the manifold allows for a decent vacuum during idle and low load conditions, where as the intake tube before the turbo does not. However, the reverse is true for load conditions, which is why this is the factory lay-out. I've tried the exhaust plumbing for load conditions, and it did not work too well. I had to plumb it back into the intake tube. Having a vacuum over just venting the air out of the crankcase provides a better situation for the rings, and you have very little if any blow-by (assuming your rings aren't already compromised due to excessive crank-case pressure). Having the vacuum helps prevent oil from passing the rings into the combustion chamber. I currently do not run a catch can at all, just the factory S14 VC air/oil separator, and I have very little oil residue. I am going to install a catch can just because, and I'll have basically no oil residue passed the catch can. There is nothing in my intake manifold as well, but the PCV valve is new so it does not allow air passage from the VC to the manifold. There are some cheap vacuum pump options you can find on summitracing, there's even a kit for the 4G63 that most likely could be adapted for an SR pretty easily (assuming you don't have an A/C compressor).

            www.2LiterTurbo.com (Personal Site)
            96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

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            • #7
              Originally posted by 2_Liter_Turbo View Post
              There is nothing in my intake manifold as well, but the PCV valve is new so it does not allow air passage from the VC to the manifold
              Did you mean from the intake to the valve cover? If its working, it should flow from vc to intake with vacuum (no boost).

              I'm thinking about either a electric or mechanical pump, or an exhaust scavenge. Reading this thread now:
              http://forums.bimmerforums.com/forum...0#post21048800

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              • #8
                Yes, sorry, lol. Typing fast at work... when I really should be doing work stuff! ha

                The exhaust scavenge does not work very well, at least with my setup it didn't. I had it plumbed on my down pipe at a 45° angle. I have a top mount GT3071R.

                www.2LiterTurbo.com (Personal Site)
                96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

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                • #9
                  Whoops double post


                  Which exhaust scavenge kit did you have??

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                  • #10
                    Yea, exhaust scavenging needs very low back pressure to work. 45 degrees also isn't great either, it needs to be more like 60-75 deg from vertical, or <30 deg from horizontal.
                    '18 Chevrolet Volt - Electric fun hatch for DD duty!


                    DefSport Koni Sleeve and Spring Perch Buy!!!
                    http://www.nissanroadracing.com/showthread.php?t=5902

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                    • #11
                      I have 3" to 3.75" exhaust, lol. Backpressure shouldn't be an issue. I know the 45 degree wasn't the best but thats where the shop put it at. Maybe 50 degrees, but around there.

                      www.2LiterTurbo.com (Personal Site)
                      96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

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                      • #12
                        Hmmm after reading this:
                        http://www.motortopia.com/dragracer/...mance-dyno-58/

                        I think I'm going for an electric pump on the motor. After seeing how much power I lost with a poorly vented system I'm very curious how much power is waiting with a crankcase under vacuum.

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                        • #13
                          Mine has too much vacuum under load and pulls oil into the intake, which then drips out after the engine stops. So I am now desperately looking for an S13.4 valve cover setup.

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                          • #14
                            ^^^ If you don't mind drilling/tapping the holes for the coil packs, I have an N/A S14 SR valve cover I'll sell for cheap. Only difference is that it doesn't have the holes (but the flats are there) and it's silver, lol. PM me if interested.

                            www.2LiterTurbo.com (Personal Site)
                            96 240SX SE: Track Car | 90 Skyline GTR: Bucket List Car | 07 Legacy Spec B: The DD

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                            • #15
                              Too much vacuum under load? I assume you mean full throttle. Unless you have a pump or exhaust scavenge, that is when it would see the least amount of vacuum.

                              What is your breather system? No baffling, excessive blowby, incorrect routing; these could all cause oil in your intake.
                              Last edited by jfryjfry; 06-06-2013, 08:03 AM.

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