stock cylinder jug can go 4 different size pistons .25, .50 ,.75, and 1.00 over.
Well, If i were you, it is better to wait, for more goodies bore kits. crank, cam, injector, exhaust pipes, bigger valves, dual valve springs and more..
some bore kits will have some fuel issue and exhaust , will need control box control injectors.
all bore kits and aftermartket exhaust willl have trail and error. it is not bolt on and go wide open throttle..
all aftermarket inlet pipe has differ sizes wont work or not.. ( dont throw the money for nothing)
im auto mechanic, I know how things work and some dont work..
As Now parts on the grom are being testing on research and developings, before they release in the market ans exports.