FWIW, years ago, after a few years of tuning with collectors, I added a 3" TTI X-pipe and Dynomax UltraFlow mufflers to their step headers on my 360 IHRA Stocker. I picked up between .05 and .10 in ET right off the bat. A number or two leaner on jetting also helped. I figure the X-pipe helped and the Dynomax mufflers didn't hurt.
