Well.....on my saga 1.5(auto...) i was using the original muffler(which is s-flow) and i changed it to one of em tembak bulan pipes(got a lil excited... )...the result-revs went up much higher...and i mean that....but gear shifting was a problem...i had to pay with the accelarator pedal for the engine to shift gears....but to get to the point of having to shift gears was never a problem....later on i changed to an s-flow muffler(2-inches)...the engine shifts much better now....or should i say it shifts the way an amt is supposed to shift....but i definately that it takes longer to rev to 4k.....Btw....i'm using an open pod filter where air gets sucked in super fast....