H-Pipe vs. X-Pipe vs. Straight-pipes

I tuned and ran open TTI 1 5/8"-1 3/4" step headers with collectors for several years. Then I added their 3" X pipe ending with 3" Dynomax Ultra Flo mufflers at the rear end housing and went faster. It was at least .05 to around .10 in the 1/4. I did remove the 60lbs it all added from elsewhere in the car to keep the weight the same and jetted down a bit for best results in my combo. But it definitely helped. (Your results may vary.)

It's just a little inconvenient when I have to swap transmissions or rear end gears.