"Yar, actually, that same video is contained in the link that you posted- it's the "Engine Masters" video showing dyne tests with H & X pipes."
Thanks Dave, I did find and watch the video. The testing was done in the 3000-6000 RPM range and HP and torque data were within about 2 HP and pound feet in that range. The various pipe configurations were not tested at RPM that an engine would run in street use so we don't know how that power delivery would be effected. The guys in the video did point out that the H and X have more effect at lower exhaust gas velocities.
They also mentioned, but did not quantify, that both types of cross pipes eliminated what they called the "burble" sound of the isolated pipes. I think they mean the sound that an inboard power boat with exhaust discharging below the water line makes. That is the reason I like and use an H pipe in my street rod. It very noticeably quiets the exhaust at low RPM.
On the Chevy Talk high performance forum I have seen data from drag strip performance on this same issue that suggests that small differences in power delivery does affect who gets to the finish line first.
