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Old 01-28-2008
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4low torque question

Had a disagreement about torque today and how much its multiplied when in 4low.

I have an 07' FX4 (4.0l 4x4)

Stock torque is 238ft. lbs I think...(little higher with my CAI)

BUT!!!! what is the torque to the wheels when 4low is engaged.

I know that the engine torque is consistent regardless of what position your transfer case is in, but what about torque to the wheels.


Any links to official stats would be helpful...or if you could explain it better...pls help

thanks OkiRanger
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Old 01-28-2008
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Quote:
Originally Posted by okiranger View Post
Had a disagreement about torque today and how much its multiplied when in 4low.

I have an 07' FX4 (4.0l 4x4)

Stock torque is 238ft. lbs I think...(little higher with my CAI)

BUT!!!! what is the torque to the wheels when 4low is engaged.

I know that the engine torque is consistent regardless of what position your transfer case is in, but what about torque to the wheels.


Any links to official stats would be helpful...or if you could explain it better...pls help

thanks OkiRanger

Your engine only puts out 238ft lbs at a certain RPM, it will vary depending on the RPM.
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Old 01-28-2008
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Originally Posted by okiranger View Post
BUT!!!! what is the torque to the wheels when 4low is engaged.
The total torque to the wheels will be what the engine actually puts out times every torque multiplier minus the drivetrain friction.

Making some arbitrary assumptions about the drivetrain will allow us to do sample torque calculations. Note that these numbers aren't necessarily true for a Ranger or for any other vehicle. They are just assumptions of possibles used to demonstrate the method:
  • total frictional loss in the drive train of 15% for a 4x4 manual and 25% for a 4x4 automatic.
  • torque converter factor of 1.8
  • the RPM at which the engine torque peak occurs can be made to coincide with the RPM that yields the converter's peak torque multiplication (this may not be realistic because the stall speed and peak engine torque often occur at different RPMs).

Examples:

Automatic:
238 lb-ft. advertised torque peak
2.47:1 first gear
1.8 peak converter multiplication
2.48 transfer case reduction
4.10 axle ratio
75% drivetrain efficiency

Max torque in 1st gear and low range:
(238 x 2.47 x 1.8 x 2.48 x 4.10) x 0.75 = 8069 lb-ft.


Manual:
238 lb-ft. advertised torque peak
3.40:1 first gear
2.48:1 transfer case reduction
4.10:1 axle ratio
85% drivetrain efficiency

Max torque in 1st gear and low range:
(238 x 3.40 x 2.48 x 4.10) x 0.85 = 6994 lb-ft.
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Old 01-28-2008
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thats exactly what I was looking for bob...thanks alot! now its time to shove it in my buddies face. lol
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