Dodge 4-Speed Auto

DODGE 4-Speed Automatic
Performance Car / Street Rod / Sport Truck


The 518/618/47RH factory overdrive transmission was designed for improving Dodge’s CAFE (Corporate Average Fuel Economy) ratings. Because of this it has a very tall .69 overdrive ratio. The GEAR VENDORS fixes the wide ratio problems so that when you want performance you have a gear between each of the factory ratios that give you approximately half the drop in engine rpm and torque multiplication (see final drive ratios).

You can easily have increases in horsepower in the 50+ range and torque boosts of 70lb ft. just by gear splitting. With 8 forward gears available the motor stays in a narrow rpm band of performance. The .78 ratio of the GEAR VENDORS gives an alternative overdrive ratio to the very tall factory gear and the GEAR VENDORS can be used with virtually unlimited horsepower (if it is 1200hp or less it gets the standard product). If you have a car or hotrod truck also read the 3-speed 2 wheel drive section. If you have a truck used for towing read also the 4-speed automatic truck section.


Find your transmission and rear gear multiplier below. The Final Drive Ratio shows you how many times the engine turns for one complete turn of the tires. This Final Drive number is also your torque multiplier when in that gear. GEAR VENDORS reputation for being the best is because of its sophisticated planetary construction. This means GEAR VENDORS is the only auxiliary intended as a GearSplitter behind automatics and the nicest to work behind both automatics and manuals. You are able to shift half gears that keep the engine in the power. Any auxiliary that requires you to let off the accelerator or is not intended to shift frequently is not going to give you this performance.

There is not room here to cover all the details so call the factory to discuss the full benefits demonstrated on these charts.

    Axle Ratio
    4.56 4.10 3.90 3.73 3.54
  Trans Ratio Final Drive Ratio
1st 2.45 11.17 10.05 9.56 9.14 8.67
Over 1.91 8.71 7.84 7.46 7.13 6.76
2nd 1.45 6.61 5.95 5.66 5.41 5.13
Over 1.13 5.15 4.64 4.41 4.22 4.00
3rd 1.00 4.56 4.10 3.90 3.73 3.54
Over 0.78 3.56 3.20 3.04 2.91 2.76
4th Dodge O/D 0.69 3.15 2.83 2.69 2.57 2.44
Double Over* 0.54 2.46 2.20 2.10 2.01 1.90
*Note: Double Overdrive not to be used when towing or loaded.

Call or e-mail the factory to find out all the options availalbe in your performance application.


DODGE/DODGE RAM 2-Wheel Drive Truck/Van 4/5 Speed Automatics

Call Factory for Application