If not mistaken, original is 2" from the extractor to the muffler. But don't bother to alter it into bigger size as it will decrease your power, if you like to have a louder or more aggressive sound, change out the whole system. You can try PM "Semperfi" as he have the whole new complete set of HKS muffler original from Japan for GTT. This might help you to get better HP and more aggressive sound.
what is the problem if RPM meter giving the wrong reading?
my car is suzuki vitara
sometimes when the car engine loud sound (means high rpm) but the rpm reading only 800
almost every time it gives the wrong...