Btw, that 40 minutes was for the cheapest Harbor Freight 3/8" impact wrench with 60 ft-lbs of torque which requires 3 cfm @ 90 psi. For their cheapest 1/2" impact wrench with 250 ft-lbs it requires 5 cfm @ 90 psi. That would be around 25 minutes of total use. I'm sure you could get a lower cfm wrench with more torque, but I wouldn't want to carry a $150 Craftsmen tool onto the trail.