Thanks man. Actually I am having a TRD muffler on. And my friend is selling his RUNX with a new 5-zigen(only 6 months). So I am thinking if I should switch. Still thinking about it. But, anyway, thanks :) Just a note: For the difference between the tone of 2 mufflers, the 5-zigen sounds a bit better at the high end...but I know it comes to a personal choice :) As for actual gain, I don't really believe just an muffler will make big difference. Plus the modifications on my car and my friend's car are different.... so will see if I can get some time in a weekend before he really sold his car, then I can try the 5-zigen on my car. :)