I don't know if this topics been discussed, I know there are 2 types of pistons for the B16A PR3 and the P30 and from what I'm told the P30 produces better compression. Heres my question I'm hoping there are some Honda Challenge guys that'll read this. I have a spare B16 I want to rebuild, however, I can not find the part number for the PR3 pistons. Would P30 Pistons be legal in H4? I'm currently in HPDE3 with NASA and one day hope to do TT and eventually H4 and would like to build it all to spec. Any help is GREATLY appriciated.