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.
I use haltech e6x in my FD, rx7. But my Original RPM meter is not work. but if i use aftermarket RPM meter can work well. anyone can help me to solve this problem