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Thread: 2.4L S Engine Case: 5R vs 7R?

  1. #1

    2.4L S Engine Case: 5R vs 7R?

    Now that my engine is apart and washed, my mechanic told me that my engine case was a 7R casting # which was better than the 5R castings. He wasn't sure why, but it got me curious. Its the matching # engine 6331702, chassis #1100. Anyone know the history or reasons why one was 'better' than the other? (ok, I have visions of a bunch of grown men crawling under there cars to look )

    PS - I looked in my 'Excellence was Expected' but it doesn't mention any mid-year changes in '73. I don't have the Peter Morgan book which may answer this. Anyone?
    Chris Purpura @civilizedmisfit
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  2. #2
    If I remember right, the 7R cases have extra reinforcement along the main webs and are the strongest of the early 911 cases.

  3. #3
    According to Wayne's new book, only 73RS and 73.5T CIS had 7R cases. Is yours a CIS car?

  4. #4

    same subject, different board...

    Chris, I checked the posts regarding the 7R engine case on the Pelican Board. I remembered previous discussion and searched with "7R engine cases" here.
    Shawn.
    67 coupe roller
    99 M96 2.5 litre
    early911s reg 447
    R Gruppe 399

  5. #5
    Goldmember ttweed's Avatar
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    Originally posted by timothfarrar
    If I remember right, the 7R cases have extra reinforcement along the main webs and are the strongest of the early 911 cases.
    They are the strongest of the magnesium cases. The very early cars had sandcast aluminum cases that are stronger. A lot of people building high performance motors prefer those over the 7R. Ask racea911 why he has a perfect, fully prepped 7R case for sale.

    TT
    Tom Tweed
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  6. #6
    Why yopurb's car has an 7R case, when all 73S's did not have it originally?

  7. #7
    Originally posted by ttweed
    The very early cars had sandcast aluminum cases that are stronger. A lot of people building high performance motors prefer those over the 7R.
    Porsche replaced the old aluminium case with magnesium in the interest of reducing rear-end weight to improve balance. Any 911 fitted with aluminium case will always be tail-nervous, even LWB. 911 is meant to corner well; it's not a drag car.

  8. #8

    OK, more 7R info...

    Bruce Anderson's Porsche 911 Performance Handbook pg. 135 ..." The...7R magnesium crankcase is the best crankcase to use when building any of the engine displacements up to 2.7 liters - and 2.8 liters if you insist. It was stronger than all but the first sand-cast-aluminum crankcases."

    "There were two versions of the 901.101.102.7R crankcase - one with 92mm cylinder spigots used for 2.0. 2.2, and 2.4 liter engines, and one with 97mm cylinder spigots for the 2.7 engines."

    pg. 136 "The 901.101.102.7R magnesium crankcase with the 92mm cylinder spigots was introduced for use with the 2.4 liter engines in midproduction. I recommend them for use with any of the smaller engines...because of thier additional strength."

    Ah, you can sleep well tonight Chris, your cases are correct. Unless you consider the quote about my 901/05 sand cast aluminum cases.

    Shawn.
    67 coupe roller
    99 M96 2.5 litre
    early911s reg 447
    R Gruppe 399

  9. #9
    Originally posted by Shawn
    The 901.101.102.7R magnesium crankcase with the 92mm cylinder spigots was introduced for use with the 2.4 liter engines in midproduction
    for CIS cars only (73.5T).

  10. #10

    only a certificate of authenticity....

    will put the issue to rest. I cannot find a reference as to fuel delivery for the 7R cases. Or I am getting lazy, The C of A's are up to $110 last I heard...the book is cheaper.

    Hope to hear the outcome. Shawn.
    67 coupe roller
    99 M96 2.5 litre
    early911s reg 447
    R Gruppe 399

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