Well I had a single 3 and went to a dual 2.25 xpipe set up! the single 3 inch created some good gains and sounded great, but Im feeling the difference with the xpipe so we will se when I get it to a dyno! Also the sounds this xpipe is making is sounding like a ferrari or a nice tuned sound exotic...the straight pipe sounded great at certain rpm's but this xpipe is unreal!!!!Stock size from? Back from the header or muffler only?? Cats? The piping size is different from the header to the rear of the muffler...