No exhaust system on the car....open headers only. But, I didn't know that the evac hoses to the headers would not work with mufflers. In fact, I have a similar engine, sbc421 c.i., 13.5:1, solid roller w/ .765 lift in another vehicle that I have mufflers on, and am using the same evac system. Have had no problems.... similar, but stronger motor. Should I be knocking on wood as I type this?