One reason V-8's need a crossover, is the fireing order. They do not fire evenly, as a six does. Draw it out and you will see the left and right banks do not alternate fireing. A crossover tube gives these uneven pulses a larger place to go, smoothing the whole thing out. A 6 into 1 header system, on a six, will develope more power but won't sound as nice (at least to my ears).
Armond
