My old pump gas Duster(518 C.I. 400 stroker motor) had a three inch system with 14x7x3.0 inch Magnaflow muffs with a side inlet and centered outlet mounted at the rear bumper. I ran it with the system on the car and ran it later with it removed, it ran 7.01 at 95.6 MPH in the 1/8 mile with it on the car and ran 6.99 at 95.8 MPH with it removed.
I swapped the heads, intake and carb.later that year and it ran a best of 9.993 in the 1/4 mile at 134.+ MPH corked up with the air cleaner on using Oregon 91 octane pump swill