the best exhausts out there gives you about 4.5 to 8 wheel hp. the kazuma gives about 9 to 14 hp.i have both a jdm pro 1 with 2.5 inch piping(not the knock offs)it gave me more than the standard TRD
,but when i changed to the kazuma,i was like what the fuc.kk!it outperformed the pro1 the exhaust is real good,the kazuma with a silencer still has better gains than a standard TRD
the silencer works,but if you really want it quiet,take the silencer to a machine shop and have them weld on a nother flange(so that it has two,one behind the other)the space between the flanges should be as long as possible,but not too long cause there is a slight curve at the end of the kazuma.
the space between the flanges,can be wrapped with a layer of fiber glass material(the one you pack into speaker boxes) this obsrbing material,along with the extra flage would reduce the noise level significantly and you would have as much gain still as most regular exhaust on the market.
KAZUMA is the king of exhausts for the 7th gen celica!