I run 3" to the rear axle with turndowns. Walker Dynomax Ultraflow. No drone and very quiet in the car until you mash the loud pedal!

'63 Dodge 330
11.19 @ 121 mph
Pump gas, n/a, through the mufflers on street tires with 3.54's. 3,600 lbs.
10.01 @ 133mph with a 250 shot of nitrous an a splash of race gas. 1.36 60 ft. 3,700 lbs.