Race mufflers
I run Dyno-max race magnums, only picked up 2 hundreths ,between mufflers on and open headers.Must flow pretty darn good! Mind you that was on a 10.1-1 compression BBC. I think the more compression, the better the motor will like open headders. I.M.O. under 12.5-1 compression, motors like some back pressure. These ar pretty quiet mufflers till wide open throtle, unlike them noisy Flowmasters