had no clue how to measure back pressure, so useful info to be had in here.
you sure the cat isn't on its way out ?
or the muffler actually muffles sound well hence back pressure build up ?
i'm current running 3" to two 2" tipped straight pipes and its about the same sound level as my 3" muffler ....under 5k rpms, at wot on high rpms its a tad louder