Description
The Tubeworks Underdrive is a must for off-road truck applications using a Turbo 400 Transmission. Simply stated, the underdrive increases the RPM of the driveshaft which allows a ring and pinion ratio to be much higher and stronger. With 37, 39, or even 42 inch tires, the need for a high final drive number becomes even more important because the underdrive allows the drivetrain to use as high as a 4.11 Ring and Pinion and have as low as a 5/83 final drive. Depending on engine RPM, top speed desired and wheel diameter, we can set you up with the proper planetary ratio and rear end combo for maximum torque or MPH.
This unit also allows for a quick interchange of planetary ratios for those competitors that wish to have an extremely low final drive for qualifying. The final drive can change from a 5.43 to a 6.29 or lower in a matter of minutes.
Pictured on the underdrive is the 8-rib pulley that is used for alternator applications. The pulley is not included in the price of the underdrive and would be an upgrade. 8-rib or v-rib style pulleys are available.
Each Planetary Underdrive is lubricated and cooled from the transmission.
THE MATH TO DETERMINE FINAL DRIVE IS AS FOLLOWS USING A 1.31 PLANET SET. (LOWEST RATIO)
1.31 (PLANET RATIO) X 3.71 (R&P RATIO) = 4.86 (FINAL DRIVE RATIO)
1.31 X 4.11 = 5.38 (FINAL DRIVE RATIO)
1.31 X 4.29 = 5.61 (FINAL DRIVE)
1.31 X 4.56 = 5.97 (FINAL DRIVE)
THE MATH TO DETERMINE FINAL DRIVE IS AS FOLLOWS USING A 1.48 PLANET SET. (QUALIFYING RATIO)
1.48 (PLANET RATIO) X 3.71 (R&P RATIO) = 5.49 (FINAL DRIVE RATIO)
1.48 X 4.11 = 6.08 (FINAL DRIVE RATIO)
1.48 X 4.29 = 6.34 (FINAL DRIVE RATIO)
1.48 X 4.56 = 6.74 (FINAL DRIVE RATIO)
(COMPLETE CHART)
1.56 X 3.79 = 5.91
1.56 X 4.11 = 6.41
1.56 X 4.29 = 6.69
1.56 X 4.56 = 7.11
1.48 X 3.79 = 5.61
1.48 X 4.11 = 6.08
1.48 X 4.29 = 6.35
1.48 X 4.56 = 6.75
1.41 X 3.79 = 5.34
1.41 X 4.11 = 5.80
1.41 X 4.29 = 6.05
1.41 X 4.56 = 6.43
1.37 X 3.79 = 5.19
1.37 X 4.11 = 5.63
1.37 X 4.29 = 5.88
1.37 X 4.56 = 6.25
1.34 X 3.79 = 5.08
1.34 X 4.11 = 5.51
1.34 X 4.29 = 5.75
1.34 X 4.56 = 6.11
1.31 X 3.79 = 4.96
1.31 X 4.11 = 5.38
1.31 X 4.29 = 5.62
1.31 X 4.56 = 5.97