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Thread: Alu engine build: 2.3l or 2.5l?

  1. #1
    Senior Member
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    Alu engine build: 2.3l or 2.5l?

    Gentlemen,
    I am currently planning having an engine built on a 67 alu case. Since the price differential between a 2.3l engine with biral cylinders and a 2.5l engine with Nikasil ones is (almost) negligible I lean towards the additional torque of the 2.5l version.

    However, I remember that the 2.5l STs had reliability issues with flywheels working lose etc.

    So, what is your recommendation on this? Both engines would use the original and balanced 2.0l crank.

    Thank you for your advice!
    Keep up the speed!

    Anatol

    '68 911S coupe
    '92 964 RS NGT
    '09 987S Boxster

  2. #2
    Anatol:

    The flywheel problems were with the 70.4 crank version of the 2.5L. The factory went back to a 66 mm crank which didn't have those problems. If you use the 66 mm crank with Nikasil barrels (90 mm) and pistons you will get a displacement around 2.506 (I think), and a very nice quick revving engine. I have one in my Kremer ST re-creation and it is a great engine.
    Gib Bosworth
    EarlySReg 434
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  3. #3
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    I have ran 2.5 SS engine's racing and street with great success for 15 years.
    I have a sweeeeeeeeeeeeeet 2.5 twin plug ready to go in my 67S street car as soon as I finish stock appearing resto. Per your observation cost same.
    Early 911S member #166

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  4. #4
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    Thank you for your feedback! That all sounds very inspiring and I think I will go for the bigger displacement!
    Keep up the speed!

    Anatol

    '68 911S coupe
    '92 964 RS NGT
    '09 987S Boxster

  5. #5
    Senior Member Neunelfer's Avatar
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    My 2.5 is built on the same case with 90's. Love it. Consider this though... MSX gear box. You'll need it to take full advantage of this motor.
    Eric - Sandy, Utah
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