me thinks these things work better on smaller engines. but, a 68, 426 hemi roadrunner came w/ an h pipe on it ! over 500 cubes , I still don't think their worth their weight, provided your whole exhaust system is big enough! . jmo
..as suggested earlier the factory installed the H pipe because it was quieter
allowing the use less restrictive mufflers on some big block cars.
i also think your final outlets have to be large enough so each side of 4 tuned
pipes (headers) will scavenge themselves.
..Yellow Rose's post also makes some informative points.
