The newer alloys containing more silicon, do not expand at the same rate of conventional billet forgings. Additional clearance does need to be added, for an increase in cylinder pressure above OE specifications. I used Mahle cast pistons in the last engine I built and added 0.0015 to the piston/wall clearance. Same applies to the ring end gap. I am sure the piston manufacturer supplies the specs. I was going to use Ross pistons, when I called they had never made a set, but said they could. Sorry didn't feel like being a guinea pig, been one of those enough as it is. Hopefully, they have some out there now, with good results.