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Thread: 901 gearing for a 2.5l engine

  1. #1
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    901 gearing for a 2.5l engine

    I run a 2.5l twin-plug engine in my 911S SWB and this powerhouse really puts the strain on my gearbox. That's why I think of having a new, stronger, and better geared box built.

    As a variation on the theme of a recent thread (http://www.early911sregistry.org/for...ad.php?t=34825), I wonder what the best gearing would be for my engine. I would be very grateful if you could give me your views regarding the following issues:

    1. I would like a top speed of 145mph at 7500 rpm in fifth. This should ensure a sensible rev level on the autobahn. With my stock gearbox, the engine easily pulls 155mpg on the speedo. And yes the car feels very light at that speed.

    I will drive the car in road events and for fun drives on mountain roads, so 2-3-4 need to be reasonably short. To prevent frequent issues, 1st should be a short gear, only for starting.

    2. Who offers modern and proven quality parts for the 901 gearbox? I already run an English Tuthill lsd and want to build the gearbox for high reliability.

    3. What further measures are typically employed to strengthen the 901 box when used with a stronger engine?

    Thank you very much for your help!
    Keep up the speed!

    Anatol

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

  2. #2
    Senior Member
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    Hi Anatol - have a look at this thread for some useful info :

    http://www.early911sregistry.org/for...t=transmission
    Andy

    Early 911S Reg #753
    R Gruppe #105

  3. #3
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    Andy, thank you for pointing me towards that thread.

    Did you go with AEJQX? Judging from the thread, this seems to be a good choice.

    Now, what can there be done to strengthen the 901-gearbox? And any recommended gear suppliers?

    Thanks again!
    Keep up the speed!

    Anatol

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

  4. #4
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    Hi Anatol - yes, I did go for A,E,J,Q,X but I haven't driven the car yet (it's still in the build stage) so can't comment on the suitability of the chosen ratios.

    One of the weak points in the (magnesium-cased) 901/911/914 transmission is the intermediate plate & a std 'upgrade' (when mating to a high power or high torque engine) is to replace this with a billet aluminium version (which has been done on mine).
    Andy

    Early 911S Reg #753
    R Gruppe #105

  5. #5
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    Andy,
    thanks again! Where did you source the billet intermediate plate?
    Keep up the speed!

    Anatol

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

  6. #6
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    plate

    Anatol-- Try Performance Products.com or Stoddards both in the USA

  7. #7
    Restoration newbie.
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    Having a SWB car your intermediate plate is aluminium already, unless
    you have a later gearbox. I believe the 1969 901/13 is the first mag
    cased gearbox (901/12 if you had a four speed)

    andy
    67S in pieces
    EarlyS: 1358
    [SIGPIC][/SIGPIC]

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