1979 F600 4x4 cold start

370 4v, with new 31" Thrush glasspacks. It's 2.25" true duals that dump before the rear axle. 2.25" exhaust will give you a little more torque in the low end, versus 2.5" which will give you a little more power in the top end. The truck has a 6.83 gear ratio, so it's going nowhere fast.