I tried them and didn't have much luck - still loud. Put the washers in and that helped a little - still too loud. Also tried the perferated cones. Also didn't help much. I have had the best luck with a pair of Summit race mufflers #638230 - under $30 each. Short piece of 3" pipe clamped to my headers ( stainless exhaust clamp ), those muffs, and down spouts dumping in front of the axle and angled towards the center of the car. Quiet enough not to PO the neighbors too much and easy to remove for the track. I also use them for any T&T on the street that I might do.