what size is that doughtnut type gasket thath goes between the header and the highflow cat HP !

and where can I get it?????

since they don't sell a lot of the parts for ours cars in the parts stores, just go to the dealer man. most sure way of getting it.

you can get that gasket on www.hondaautomotiveparts.com or at the honda dealer. It is about $10 though.