[5GSS]

Read this:

http://www.boyleworks.com/ta400/psp/exhaust3.html

A crossover, which is an interconnection between both sides of a dual exhaust system somewhere in front of the mufflers, has been used by automotive manufacturers to reduce sound levels and increase performance. A crossover lets the constantly changing pressure in both pipes equalize by letting each half of a V-type engine simultaneously use both sides of the dual system. In other words, the crossover helps minimize the negative effects of back pressure. Most crossovers look like an "H"; however, another type of crossover has been recently introduced that looks like an "X".

By reviewing the data in figures 8-10 (below), it can be seen that when comparing the H and X types, the X crossover not only reduced 60 foot times and quarter mile times but increased trap speed as well. Functionally, the difference between the X and the H is, the X type forces the exhaust to cross between both sides. Based on the performance increases we noted with the X crossover, the scavenging forces created by the gasses crossing over in this way appear to be stronger and more effective across a wider range of engine speeds.