I have seen 2 home made dual pipe set ups and 1 that was done at a muffler shop. The difference in sound is not a lot different than a single straight pipe, but you can definetly hear that sucking sound from the turbo when you shift on the manual trannies. There really is no advantage to having dual pipes over a single staight pipe, the turbo is the biggest restriction once the muffler is gone. You should also be careful how you split the single to dual, if it is not done well you could put a restriction in the pipe and hurt flow. i do not know of a dual system for sale for our trucks, I think they are one off type of deals.
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