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.
Been modding till stage 2 . Semi auto gear box start to clutch slip . And circlip bearing broken need to be fix . What do you guys think ? Semi auto or manual Awd ? Cos price to fix the semi auto gear box are round...