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Shaving i head

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    Shaving i head

    I have an i head laying around (w/related electrics) and want to do the ol' put it on my eta block mod. I've searched but can't find out how much material I should remove from the head to retain a 9:1 CR. I also plan to use a stock head gasket.

    Thanks in advance for any and all help.

    #2
    -I'm sure you can shave it some, but not enough to keep 9:1 CR. You have to use an adjustible cam gear, tho.
    1989 cirrisblau-metallic 325i

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      #3
      to retain the same CR you need to remove ~5cc (difference in head chamber volume) which if you decked the block would be 0.9mm so it would be a tad more than 0.9mm off the head since its tapered. I would look at the machining allowance recommendations in the Bentley before doing it.
      89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

      new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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        #4
        The Bentley lists the "new head thickness" at 125.1mm and the "after machining thickness" to be 124.7mm. Difference is only .4mm so I guess it's a no go.

        Thanks for the info guys.

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          #5
          Just buy some Super Eta pistons (1988 ) seta. I wouldn't shave anything unless it is worped or pitted. And before you put the seta pistons in have valve reliefs cut in to them, for good insurance.

          Then again I would buy some custom pistons that already have valve reliefs in them and are made to run with the i rods. That is a true stroker.

          1986 325es (69k) Garage Queen Buy It Now 10k;1986 325es (track rat) 2.7i How-To & 1.1/1.3Motronic UpGrade
          1991 318is (daily driver) 1991 318is M42 Maintenance How-To;1989 325i (parts car)

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            #6
            You wont make a noticable difference by shaving the heads on the 885 casting as there isnt much to work with in the first place. We decked serveral heads up to .020 and thats a LOT, after that you are compromising the bowl of the combustion chamber and can lead to compression loss.
            Super eta rods and pistons will get you to 8.5:1 compression ratio and are meant for the 885 casting from the factory, and have valve reliefs in them from the factory. Thats more than enough for a naturally aspirated engine but tends to be a dog with a higher lift camshaft where that calls for a higher static compression ratio.

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              #7
              Originally posted by kenika65 View Post
              Then again I would buy some custom pistons that already have valve reliefs in them and are made to run with the i rods. That is a true stroker.
              -Metric Mechanic is your friend here. Your expensive but reliable friend.
              1989 cirrisblau-metallic 325i

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