If you want to know which electric impact wrench has the most torque it is the Milwaukee 2767-20 1/2″ High Torque Impact Wrench which delivers almost 1000 torque ft.lb, which is a battery powered cordless impact wrench.
If you want to know, an impact wrench with air power is Ingersoll Rand 2850MAX-6 1″ Extended Anvil Impact Wrench which comes with a powerful torque that is 2100 Inch Pounds.
Also Check: The Most Powerful 1 Inch Impact Wrench (Heavy Duty Impact Gun)