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Thread: 69S Transmission Ratios and Tranny Noises

  1. #1
    JuanLopez
    Guest

    69S Transmission Ratios and Tranny Noises

    I have a problem with one of my 69 911S. It is the one I use for track events and it has developed a whine on 4th gear only when the tranny is warm and running at a constant speed. Is this "the problem" with the intermediate plates?

    Also, I'm looking in to rebuilding the box and taking advantage to optimize my gears for Sebring/Daytona/Homestead/Road Atlanta and VIR. Any suggestions on gear ratios (or letters), I use stock 15" fuchs with 205/50's and my target RPM is 7000.

    My motor is a slightly modified 69 2.0S with Webers and MSD (for now anyway!)

    Your help is appreciated. Juan (69 S Street and 69S track)

  2. #2
    ttweed
    Guest
    Juan-

    I'm no expert, but if it only happens in 4th gear, doesn't that indicate it is a problem with that gearset alone? Wouldn't it be more generalized, otherwise?

    If gears aren't meshing well, they can whine, but so can bearings that are going south.

    If you're going to change gearing anyway, then you can check it out. Otherwise, I would try changing the lube and see if it makes any difference. A lot of people swear by Swepco, but I use Redline synthetic in mine. It's a good chance to take a look for any large metallic chunks in the case, too.

    I thought the 901 "intermediate plate problem" was just due to flexing in high horsepower applications, but I will leave it to the more expert to expound on that. If your engine is only "slightly" modified, that shouldn't be a problem, no? You aren't making more than 200HP w/ a 2.2, are you?

    There are a couple of good gearing chart sources on the WWW, but they are mostly for the 915 and G-50 trannies, but you should be able to plug in your ratios, ring and pinion and tire size. Dr. Steve Timmins has some, including one in an Excel spreadsheet you can plug your own values into at
    instant-g.com/index.html
    Scroll down and look under the DATA heading. I'm not sure how the links function works on this ezboard, but the URL is
    http://instant-g.com/index.html, just in case.

    I don't know anything about the SE tracks you mention, being a left coaster myself. but I wish I could run them some time.

    Good luck,
    TT

  3. #3
    JuanLopez
    Guest
    Hi TTweed,

    Thanks much for the information. I have a 2.0 dynoed at 210. I'll check the tranny info.

    Thanks again, Juan

  4. #4
    ttweed
    Guest
    Wow! 210HP from a 2.0? That's as much as the factory 2.7RS engine! I think the most they ever got out of a full-race Porsche 2-liter Carrera-6 was 230, and I'm not sure if that was the old DIN figure or SAE.

    I do know that was with 906 cams, 12-1 compression, 46 IDA Webers and racing valve springs to allow running the motor to 8200 RPM. What did you do to yours to get that kind of power?

    My anemic 2-liter "S" motor dyno'd at about 138 HP to the rear wheels at 7,000 RPM, but it is totally stock. The factory advertised it as 160HP in 1967, but I think this was DIN HP at the flywheel.

    TT

  5. #5
    JuanLopez
    Guest
    The trick is, the motor is a "hand granade" 14.5 to 1 compression custom pistons with deep pockets for the valves, titanium con rods, 906 cams and aluminum cam gears fully balanced, twin plugged with electromotive, webers, redline at 8700. Must use 112 or higher octane racing fuel (VP "purple"). Exhaust are anti-reversionary headers with cookie cutters (from GT Racing).

    It will last approximately 30 hours if you let it warm up properly. The power band is very narrow making basically no power under 5500 RPM.

    I'm building a milder motor to be able to use pump fuel and get longer engine life. (it gets very expensive at the time to rebuild). That is the MSD equipped engine I have and I'm planning on using once it gets time to rebuild again. (slightly higher compression pistons, MSD with 7000 rpm chip, mild cams, webers, header and cooie cutters).

    Edit: When I say dynoed, I should say "my mechanic says it dynoed ...".


  6. #6
    ttweed
    Guest
    WHoa! I thought you said "slightly modified"! That's a full race motor!

    I can see why you're building something a little less radical. I wouldn't want to have to be freshening my motor every 30 hours.

    Good luck,
    TT

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