your no really gana change the reliability of the bike if you do to much. just make sure you do the right things. like i had an rm 80. it had .60 over bore,.30 shaved head,28mm kihen,boyson reeds,jeted out,fmf pipe,welded crank,timing advance, and it was ported and polished it doesnt sound like alot but it was alot of work done to an 80. plus with every thing else done to it i changed the sprockets out factory connection suspension.etc.etc.etc i never drilled out the air box though i never thought about it. but welcome. and dame cant belive you waited 2 years to say anything.