2mm will make the different already. More air to go in to the air chamber and combusion room. That's why some bore it until 64 or 67mm... After market TB like Jun is 70mm at inner diameter. But bigger doesn't mean better, big enough for ur engine OK lar. Don't tell me a stock b16a is going to put a 67mm or 70mm TB.
As for the above stated. im in the middle of dilema. just converted my EJ8 4door to B16B. Well of course engine are left standard. The only upgraded items are Full piping works up to a back muffler..still retain the...