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diff change for 355

Discussion in '348/355' started by ndnbill, Jan 18, 2012.

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  1. ndnbill

    ndnbill Karting

    Mar 3, 2009
    70
    Las Vegas
    Full Name:
    William
    #1 ndnbill, Jan 18, 2012
    while I have gone through 2 911T's, a cayenneT, E60M5, CLK63BS, and F430--I have kept my '03M3. For me it is close to perfect. About 6 mos ago I replaced the suspension and put in a shorter differential from Dinan. Upped the torque by about 8-10%. Truly the best bang for the buck. As long as I can keep it hooked up not many cars can pull it.

    So--does anyone know why we don't see the same thing offerred for our 355's. With a final drive of 2.8:1 it and a top speed of 180+ it would seem to be a good candidate for a shorter final drive. If it is even close to the improvement in drivability I got with the M3, I would gladly accept the MPG loss.

    I assume it has to do with where the diff is in the 355 and the cost, but curious as to what those here who really know what is going on think on this subject.
     
  2. BLAMPEE

    BLAMPEE Man Card Status: Never Issued

    Jun 28, 2008
    15,424
    Sunny Heavenly Beautiful Arizona
    #2 BLAMPEE, Jan 18, 2012
    Last edited by a moderator: Sep 7, 2017
  3. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    13,570
    San Carlos, CA
    Full Name:
    Mitchell Le
    #3 yelcab, Jan 18, 2012
    The V8 series from Ferrari has never been about absolute acceleration. If you really want that, go for the V12 models. Or, keep your M3. I, for one, would not want the lower MPG on my 355. It is already thirsty enough compared to all my other cars.
     
  4. roadracer311

    roadracer311 Formula 3

    May 6, 2009
    2,398
    San Francisco
    Full Name:
    Paul
    #4 roadracer311, Jan 18, 2012
    Probably the easiest way to lower the gearing of a 355 would be to put 17"wheels on the back, or use very low profile tires.

    The ultimate determination of how fast you will accelerate (assuming good traction) is just power to weight. Lower gearing in 1st gear helps some cars get into the RPM range, more quickly, where maximum power is produced. Once you're out of 1st gear, keeping the RPM's in the power band depends on shifting, not so much the final drive ratio.

    I'd leave the gearing alone. (and the wheels/tires)
     
  5. bobzdar

    bobzdar F1 Veteran

    Sep 22, 2008
    6,895
    Richmond
    Full Name:
    Pete
    #5 bobzdar, Jan 18, 2012
    I don't know that it would help much as the 355 is traction limited in 1st gear with normal street tires anyway. It's final gear ratio is actually 4.35:1, hence it runs about 3500rpm at 80mph even in the .84:1 6th gear. If you were to put a more agressive rear gear in, you would spend all your time shifting and likely slow the car down...
     
  6. gsfent

    gsfent Formula 3

    Nov 16, 2009
    1,101
    PB County, Florida
    Full Name:
    Jerry
    #6 gsfent, Jan 19, 2012
    All gearing choices are compromises. Unless Ferrari made bad choices with the tranny gearing or the ring and pinion, there is no real need to change.

    Tire changes will have negligible impact, maybe 2-3%. My buttometer is not that highly calibrated.

    Again, depending on Ferrari's choices, steeper gearing might not yield any quicer acceraltion times over a given distance.

    If you can spin the tires in 1st gear, you can't get any more power to the ground. So more gear is useless there.

    Additionally, while you will accelerate quicker to a given engine rpm, you will not necessarily get to a given speed quicker. That is because at the top of each gear, you will be going slower (less max speed in gear). When you then have to shift to the next gear sooner, your total torque (engine torque x tranny ratio x diff ratio--ignore tire size) will be less. So the guy who is still in the lower gear near redline is putting out more torque and theoretically more acceleration until he has to shift. Dependng on everyone's shift points and distance, it is hard to say who is faster in a given distance. If you think quarter mile and the deeper gears get you to 4th before you trap vs, the guy who has taller gears and only has 2 shifts instead of 3, well, most time the guy with only 2 shifts wins. Acknowledging that is simply a single data point.

    Now, the car will generally feel faster in each gear, but you are not necessarily getting to the same speed quicker, just to the max rpm quicker. Some people like the feel and don't mind the tradeoffs (fuel mileage and engine wear, both small items) for the feeling of quicker acceleration, or at least quicker acceleration in gear.

    Regards,
    Jerry
     
  7. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    9,728
    #7 Mitch Alsup, Jan 19, 2012
    348 std
    Crown Gear 26/27
    Drop Gear 19/20
    Bevel Gear 16/55 std 16/57 usa

    355 std
    Crown Gear 25/29 std 25/27 swiss
    Drop Gear 19/20
    Bevel Gear 16/57

    Given this data, the 355 box already has the best gears in the crown, drop, and output gears one has to choose from. Where best means the gears the give the most torque multiplication.

    Taken al together, the 355 has an EFFECTIVE differential ratio of 4.41:1.
     

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