Gears For Automatic

Discussion in '2010 - 2014 Specific Tech' started by gtrosema, Aug 20, 2014.

  1. Just bought a 2014 GT convertible. And am not familiar with the 6 spd automatic. I had a 04 Mach 1 and loved the 4.10 I put in it. Am debating on 3.55 or 3.73, Wife thinks it is fast enough already with 3.15 ...well you Anyone with either give me your thoughts,
  2. I am having the same delima I would like to know rpm at 75 mph 355 & 373
  3. Just do the math.
  4. Whats the formula
  5. Take yourr current gear ratio and subtract the difference between the two. 3.73 - 3.15 .58 so around 580 rpms. Roughly
  6. I have spoken with speed shop I am dealing with ( Maximum Velocity) and Tracy said that the 3.15 rear gears and the gears in the tranny are a perfect setup. She said that if you go with a shorter rear, hookup will suffer. Will develop too much wheel spin.
  7. Mustang Bob:

    I just read another 'gears for auto' thread on another board and the fellow installed 3.73's and found 1st gear useless and traction was tricky. A reply to the OP's question was 3.15's (or 3.31's, max). I don't know anything about the new A6 but the usual gear swap has to be much more carefully considered. That's all I can offer, lol, but it sounds like your speed shop gave you some excellent advice. A tune is highly recommended (gets rid of throttle lag, quickens shifts, improves shift points, etc., etc.,) but you have to be cautious or your warranty will be voided. If Ford offers a ProCal tune for autos then that is a good bet (I have the M6 ProCal tune on my '12 and it is mighty fine, imho).


  8. gtrosema,

    I think you mean take the ratio of the new gear to the old gear and apply the factor to the old RPM to get the new RPM:

    Say, 3.15 gears at 2500 RPM is the basis. What will the RPM be if 3.73 gears are installed?


    New RPM = 3.73 / 3.15 * 2500 = 1.1841 * 2500 = 2960 RPM

    Or, we can say that the new RPM is 18% higher than the old RPM:
    1000 ---> 1841 RPM
    3000 ---> 3552 RPM
    6000 ---> 7105 RPM