thanks for the info rc racing dude.
for me, 3port or 5port doesn't matter. no legality issues here.
i was thinking that in general, 3port engines has better low-end and 5port ones has more top-end.
even when i looked at the rb website, the 3port rody has more torque than the 5port rody.
but i guess that the 5port will have more power overall...