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Thread: M20B25 compression without opening the engine?

  1. #1
    Join Date
    Jan 2016
    Location
    Buenos Aires, Argentina
    Posts
    62

    Default M20B25 compression without opening the engine?

    Hi guys, is there any way to know the compression ratio of the engine, without opening it?


    My car was manufactured on nov 1988, its a euro 525i, no cat. Thanks for any help.




    VIN info:


    Vehicle Identification Number WBAHC210904237760
    Type HC21
    Model 525i - EUR
    Development Code E34
    Chassis LIM
    Steering LL
    Doors 4
    Engine M20
    Displacement 2.50
    Power 125
    Drivetrain HECK
    Transmission AUT
    Color Royalblau Metallic - 198
    Upholstery Indigo Leder - 0293
    Production Plant
    Production Date 1988-11-14


    Options
    200 Katalysator - Entfall Katalysator - Entfall
    226 Sports Suspension Settings Sportliche Fahrwerksabstimmung
    314 Heated Windscreen Washer Nozzles Frontscheibenwaschduesen Beheizt
    355 Laminated Glass Verbundverglasung
    401 Sliding/vent Roof, Electric Schiebe-hebedach, Elektrisch
    411 Window Lifts, Electric Fensterheber,elektrisch Vorn/hinten
    498 Headrests In Rear, Mechanic. Adjustable Kopfstuetzen Im Fond
    534 Automatic Air Conditioning Klimaautomatik
    553 On-board Computer Iv W Remote Control Bordcomputer Iv Mit Fernbedienung
    570 Stronger Electricity Supply Staerkere Stromversorgung
    651 Bmw Bavaria C Reverse Bmw Bavaria C Reverse
    823 Hot Climate Version Heissland-ausfuehrung
    850 Add Fuel Tank Filling For Export Zusaetzl. Tankfuellung Export
    856 Language Version Spanish Sprachversion Spanisch
    925 Shipping Protection Package Versandschutzpaket
    E34 525i '88

  2. #2
    Join Date
    Dec 2003
    Location
    Eastern Tennessee USi
    Posts
    14,575

    Default

    9.7:1
    95 E34 530I V2.17
    ===========
    Those who make peaceful revolution impossible will make violent revolution inevitable.

    John F. Kennedy

  3. #3
    Join Date
    Jan 2016
    Location
    Buenos Aires, Argentina
    Posts
    62

    Default

    Sh*t, i thought so ... there goes my easy way to boost it. i guess ill add a thick MLS gasket to the shopping list.

    thx for the reply.
    E34 525i '88

  4. #4

    Default

    Quote Originally Posted by Coyote_ar View Post
    Sh*t, i thought so ... there goes my easy way to boost it. i guess ill add a thick MLS gasket to the shopping list.

    thx for the reply.
    How thick would a gasket have to be to drop compression by 1 unit?

    deleted air conditioning

  5. #5
    Join Date
    Dec 2003
    Location
    Eastern Tennessee USi
    Posts
    14,575

    Default

    Quote Originally Posted by Rustam View Post
    How thick would a gasket have to be to drop compression by 1 unit?
    Appx .030 in

    Edit .030 is appx .5 points so .060 is around 1 point.
    Last edited by 632 Regal; 11-26-2017 at 03:01 PM.
    95 E34 530I V2.17
    ===========
    Those who make peaceful revolution impossible will make violent revolution inevitable.

    John F. Kennedy

  6. #6

    Default

    Quote Originally Posted by 632 Regal View Post
    Appx .030 in
    Doesn't make sense. .03" is a hundredth of the piston's travel between TDC and BDC:
    .03" = .75mm
    M20 Stroke = 75mm = 100*.75
    (Also had some beer so maybe thinking out of place. Would have to do normal calculations)
    Last edited by Rustam; 11-25-2017 at 04:02 AM.

    deleted air conditioning

  7. #7

    Default

    To lower compression to 8.0:1 for example, additional 2.1 MILLIMETERS must be provided. Got calculations, cannot upload through smartphone. Will upload once I get the computer connected to internet in another room.
    SO, it seems Jeff, you ARE RIGHT. I should have calculated for 8.7:1 for a unit drop as I asked earlier, but it seemed that compression is not applealing as a turbochargeable one , so did 8.0:1 example.
    Last edited by Rustam; 11-27-2017 at 09:38 PM.

    deleted air conditioning

  8. #8

    Default

    Quote Originally Posted by 632 Regal View Post
    Appx .030 in

    Edit .030 is appx .5 points so .060 is around 1 point.
    Good stuff.

    deleted air conditioning

  9. #9

    Default

    Have you consider making a gasket from a copper sheet, of agiven thickness? Must be annealed

    deleted air conditioning

  10. #10
    Join Date
    Dec 2003
    Location
    Eastern Tennessee USi
    Posts
    14,575

    Default

    Thicker gaskets can simply be purchased. Many choices here:

    http://www.cometic.com/c-1280264-aut...d-gaskets.html
    95 E34 530I V2.17
    ===========
    Those who make peaceful revolution impossible will make violent revolution inevitable.

    John F. Kennedy

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