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Thread: Crankcase ventilation for boost

  1. #1
    Join Date
    Dec 2005
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    Melbourne, Australia
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    E24, E34 x2, E36

    Crankcase ventilation for boost

    Thought I’d have a go at asking here. Have a E34 540i manual running 14psi of boost with a vortech b3.

    At a trackday last Saturday unfortunately oil started leaking out the discharge pipe to atmosphere from the catch can.

    I was looking at perhaps running a vent direct from each cam cover then running a vaccum pump to keep the crankcase back in vaccum rather than positive pressure. There is not a huge amount of info about this on the net. From the limited info about it most seem 14-16” of vaccum will also be beneficial to power generation and help minimise “blow by”.

    Anyone else had experience with this. Is an electric pump sufficient or do I need a mechanical belt driven one.


    Thanks in advance
    BMW’s
    90 E34 M5
    84 E24 M635csi standalone ecu with coil on plug
    94 E34 540i/6 SC 5-17psi Flex fuel/standalone ecu
    97 Z3 2.8
    97 E36 M3 euro SC still u/c


    OTHERS
    11 Audi S5 APR stg2
    19 Volkswagen Amarok V6


  2. #2
    Join Date
    Jan 2007
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    '86 325e, '14 VW EPA
    I don't know about an electric pump but my engine is drysumped and I have the vacuum control valve set to 7psi. I can tell you that with 3 stages of scavenging, at 900whp the vacuum was dropping. I've since changed from 1.2" spur scavenge stages to 1.5" roots. I don't know what kind of electric pump you'd need to be able to do the same. But you also need to address a way to separate the oil you will be sucking out. There will be a bunch suspended in the crank case that will condense after you draw it out but there is also a bunch of it being flung around so unless you have a good baffling system, the oil will be getting spat out of your suction port into your pump. Drysump pumps are meant to scavenge oil and also draw vacuum so the oil is then deaerated.
    Last edited by TheJuggernaut; 04-23-2019 at 12:38 PM.

  3. #3
    Join Date
    Aug 2003
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    Dallas, TX
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    Z3M, X5M
    I had the same issue the last time I was at the track. I recently changed the catch can to a sealed one that could connect to the intake tube pre-supercharger for vacuum. Hopefully this would help when I have the car running again.
    -Phil

  4. #4
    Join Date
    Dec 2005
    Location
    Melbourne, Australia
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    E24, E34 x2, E36
    The only problem with connecting to the intake is I run a blow through MAF. It would get coated in oil film.
    BMW’s
    90 E34 M5
    84 E24 M635csi standalone ecu with coil on plug
    94 E34 540i/6 SC 5-17psi Flex fuel/standalone ecu
    97 Z3 2.8
    97 E36 M3 euro SC still u/c


    OTHERS
    11 Audi S5 APR stg2
    19 Volkswagen Amarok V6


  5. #5
    Join Date
    Aug 2003
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    You might be able to use a secondary-air-pump. They should pull about 4 in. some drag racers use vacuum pumps that run off the accessory belt. not sure how well they work for street application.
    -Phil

  6. #6
    Join Date
    Mar 2011
    Location
    Neverland
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    1,834
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    E34 525i
    Quote Originally Posted by Z-Thrizzle View Post
    You might be able to use a secondary-air-pump. They should pull about 4 in. some drag racers use vacuum pumps that run off the accessory belt. not sure how well they work for street application.
    i have been planing on using a SAP in this manner, my car was manual swapped so im thinking of wiring it to trigger from the kickdown switch for both longevity and cause its loud.

  7. #7
    Join Date
    Dec 2005
    Location
    Melbourne, Australia
    Posts
    1,903
    My Cars
    E24, E34 x2, E36
    The electric pump triggered via a low boost pressure switch seems like the go. Thanks for everyone’s help on this subject. Next question so what pump is the best and where do I get it from.
    BMW’s
    90 E34 M5
    84 E24 M635csi standalone ecu with coil on plug
    94 E34 540i/6 SC 5-17psi Flex fuel/standalone ecu
    97 Z3 2.8
    97 E36 M3 euro SC still u/c


    OTHERS
    11 Audi S5 APR stg2
    19 Volkswagen Amarok V6


  8. #8
    Join Date
    Jan 2004
    Location
    Chicago
    Posts
    2,799
    My Cars
    '99 M3
    I'm about to put in one of these Cobra pumps. Hopefully it works. There is all sorts of stuff on the net about these units.

    https://www.m5board.com/vbulletin/e3...rger-m5-2.html
    TEC-3R, T4 GT40, WISECO, EAGLE, SUPERTECH, O-RING'D "FRANKENSTEIN" STROKER.

  9. #9
    Join Date
    Oct 2005
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    Northern California
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    95 M3, 15 Golf TDI wagon
    Those Cobra pumps look pretty cool. Only $80 on ebay.

    -WTB: OEM Class 2 LTW GT wing with risers- Mazak

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