een x in je pijp helpt op toeren beter om de gassen af te voeren. ,maar voor sommige doet het af aan motor/uitlaat geluid, een H-pijp doet hetzelfde , alleen is deze uitgewerkt na de 3000rpm ongeveer, omdat de gassen dan zo snel voorbij gaan, dat ze de crossover missen..
hier een stukje van een "carcraft" artikel
For any performance exhaust system, some type of crossover connecting the two sides of a dual exhaust system is important because it acts to balance the two banks of the engine. The common H-style crossover is good at balancing sound pulses between the two halves, but does little to promote scavenging because the exhaust gases tend to follow the path of least resistance, which is straight through each pipe rather than taking the 90-degree turn through the H-pipe into the other half of the system. In an X-pipe system, however, where the two sides of the system intersect, the gasses have no choice but to intermingle as they pass through the junction. This promotes improved scavenging effects by smoothing out uneven exhaust pulses from the engines firing order. It also helps quiet down the exhaust, resulting in a mellower, less raspy tone. According to Magnaflow, the faster acceleration of the gasses through an X-pipe causes them to flow in a linear fashion parallel to the walls of the tubing rather than tumbling. This laminar flowing gas is much quieter than tumbling gas, resulting in an exhaust tone up to 8 decibels quieter than a traditional H-pipe.
en hier mn Mustang, 351ci, niet geheel standaard uhm.., met uitlaten eindigend voor de achteras, met 3" X-pijp en na de X wordt het 2.5" in Flowmasters 40-series.
http://www.youtube.com/watch?v=jgajDXKCeZ0http://www.youtube.com/watch?v=s7-tQu4C0Gc