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Thread: 915/02 Trans

  1. #1
    Phil Rowe

    915/02 Trans

    The sporto recently failed in my73 s and I am looking for a reasonably priced 5-speed replacement with or without pedal box etc to complete the conversion. Would like the 02 series because I am told this will give me the best final gear and acceleration for my car and I preferr to have the correct unit since I am in the process of restoration. I am new to this so I welcome any advise also. Thanks for any help

    Phil Rowe or 925-943-6597

  2. #2
    Phil, are your a member of the S registry? If so, I've got a strong hint for you. The only guy I know who has converted a sporto car to a 915 transmission is our Austrailian newsletter correspondent, Mike Gillies. His e mail is in the newsletter. If no closer source of info as to what's involved, he could at least give you a clue. From what I understand, it's quite a chore, but not insurmountable...

  3. #3
    Roland Kunz

    Ups only the last threat on display.

    I think I wantet to ask about the engine and what tires you will have also how will you drive the car ?

    Done several sporto to shift where is your problem ? Also with sporto is in the car 905 or 025 ?


  4. #4
    Phil Rowe
    The engine is a stock 2.4 S. The car will be driven for fun, I don't expect to race it since it is a Targa. I will upgrade the tires slightly without changing from the stock wheels. My problem is getting that right trans for the 2.4 engine. I understand I need a 7/31 final drive but don't know if the gear ratios matter that much. I do want to get to 4500 RPM as quickly as possible and have the best acceleration possible to 75mph with a reasonable 5th gear for highway cruise. I have been told to stay away from a 72 915 because the main seal is hard to change but if I rebuild it now that may not matter. Do the 74-77 mag trans look and work the same as the 73. Thanks for your input

  5. #5
    Phil Rowe
    Another question. Do you know how much the acceleration changes from a 7/31 to 8/31 final drive. I have been told a lot and very little. Thanks

  6. #6
    Roland Kunz

    Now frist thing is the transmission does not make power.

    Porsche did deliver a trany suitet to the most driving needs.

    One is topseed in 5th gear.
    But you also could order other gearings. Porsche offerd up to 6 setups in there cataloge mostly named after race types ( Berg, Flugplatz, Schnell, Standard, Nürburgring, Hockenheim ) that where suitet for. The final drive is selecting there general top speed range as you can´t work to much with gears.

    Now this issue would need so much to write and explain that I have to spend hours on a subject that is totally "unimportant".

    The fact is as long you don´t understand whats really up and know what you need stick to the original trany.

    And ask your experts for more background. Then look what Porsche offered from the factory and learn to read the transmission charts ( You will find them in your manual or can order them from a serious trany builder )

    The experts will say a shorter gearing will boost ET. And they are generaly right.
    But shifting needs time and a long geared first gear that will go up to 60mph at 7500 can beat you when you have to shift twice and don´t like to use the race style shifting ( no real clutching, you just pull trough and replace the gear on a regular basis). Now with the 2,4 S you have not enough low end for a good start in a longer first ( except you have lightend the body ) but a 3,0 will pull that.

    Now if you will go tracking the shorter gears give you better control in the curves and that makes more sense as it boosts your track time and gives you more control on the wide out drifting situations.

    In my young times I made an other trick.
    You go tracking with lower profile tires shorting all gears and lowerd COG.

    Under the week you drive the high profile tires.
    Here in germany high speed driving is a important issue.

    To win races you have to be more smart then powerfull.

    So now sit down and think about what you will need and then it will be Flugplatz ( Airfield ) the optimal layout for the american needs for low ET on the straight ).

    Then get a tire chart and look what happens if you step down from 185/70/15 to 205/60, 195/60, 185/55/15 or the 195/50 profile. Compare prices for a set race rims ( look doesn´t matter ) and tires to your trany prices.

    Said enough on that, the conversion is the major act.

    As far I remeber all 915 up to 1975 have the seal ring inside the housing. You will see it if you look at the TOB guiding tube. If it is as screwed on unit it is easy to renew the seal ring. 77 on tranys have a electronic speedo.


    BTW: Can someone explain me the trick to have the whole thread in the answer. Sometimes it works but mostly I have only the last reply.

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