Ford super duty 3.31 rear end. Will it be a big mistake. ?
Pulling a 37 foot Cedar creek with a f350. Diesel. Would the 3.31 rear end work or should I get the 3.55?
Forum Discussion
This has been beat to death on recent threads.
With the 8/10speed transmissions, the rear end ratio doesn't make much difference.
- With 1 key exception, if you would be over the max tow limit with the lower numerical ratio.
What the engine will see is it needs to provide roughly the same RPM/Torque for the same speed regardless of rear end. The transmission will select a gear that makes that happen.
You might run in 7th instead of 8th but who cares if the motor is running at the same RPM/Torque output?
In the old day's of 3 or 4 speed transmissions, it made a big difference because there was so much room between gears that if you dropped down a gear, you could miss the engines RPM sweet spot (peak torque/HP) and it would result in running at excessive RPM. Using a higher (numerical) rear end could compensate by adding to the torque allowing you to stay in a higher gear. With 8/10 gears and motors designed with flat torque curves (not to mention massive torque compared to 20yrs ago), the truck can always keep the motor running darn close to ideal RPM for conditions.
With the 8/10speed transmissions, the rear end ratio doesn't make much difference.
- With 1 key exception, if you would be over the max tow limit with the lower numerical ratio.
What the engine will see is it needs to provide roughly the same RPM/Torque for the same speed regardless of rear end. The transmission will select a gear that makes that happen.
You might run in 7th instead of 8th but who cares if the motor is running at the same RPM/Torque output?
In the old day's of 3 or 4 speed transmissions, it made a big difference because there was so much room between gears that if you dropped down a gear, you could miss the engines RPM sweet spot (peak torque/HP) and it would result in running at excessive RPM. Using a higher (numerical) rear end could compensate by adding to the torque allowing you to stay in a higher gear. With 8/10 gears and motors designed with flat torque curves (not to mention massive torque compared to 20yrs ago), the truck can always keep the motor running darn close to ideal RPM for conditions.
