Originally Posted by mopowar

Usually you would want to downsize as you go through the system. The idea is that as the exhaust gas cools it contracts, so you want the pipe to accomodate that contracton in order to maintain velocity. Many performance shops use a laser thermometer to try and ascertain where to downsize. Old school they would just note the discoloration of the pipe. All this is academic though without a good set of headers to start with. If it was me, I would just put something on there now that sounds good and wait for someone to develop a good set of long tubes before I dropped a bunch of cash into the exhaust. Without the headers, the gains will be minimal anyway.

The worst thing about owning a new vehicle is waiting the aftermarket to catch up.